diff --git a/.gitignore b/.gitignore index 4945221..0fa22b2 100644 --- a/.gitignore +++ b/.gitignore @@ -5,6 +5,8 @@ *.txt *.upload *~ +\#* +.#* .refcache .tags .targets.mk diff --git a/draft-schaad-cose-rfc8152bis-algs.xml b/draft-schaad-cose-rfc8152bis-algs.xml index 8d13e90..c872ecd 100644 --- a/draft-schaad-cose-rfc8152bis-algs.xml +++ b/draft-schaad-cose-rfc8152bis-algs.xml @@ -1,6 +1,6 @@ + ]> @@ -9,10 +9,11 @@ - + - CBOR - Algoritms for Object Signing and Encryption (COSE) + + CBOR Algorithms for Object Signing and Encryption (COSE) + August Cellars
@@ -39,6 +40,15 @@ This document along with obsoletes RFC8152. + + + + The source for this draft is being maintained in GitHub. + Suggested changes should be submitted as pull requests at . + Instructions are on that page as well. + Editorial changes can be managed in GitHub, but any substantial issues need to be discussed on the COSE mailing list. + + @@ -47,7 +57,7 @@ There has been an increased focus on small, constrained devices that make up the Internet of Things (IoT). One of the standards that has come out of this process is "Concise Binary Object Representation (CBOR)" . - CBOR extended the data model of the JavaScript Object Notation (JSON) by allowing for binary data, among other changes. + CBOR extended the data model of the JavaScript Object Notation (JSON) by allowing for binary data, among other changes. CBOR is being adopted by several of the IETF working groups dealing with the IoT world as their encoding of data structures. CBOR was designed specifically to be both small in terms of messages transport and implementation size and be a schema-free decoder. A need exists to provide message security services for IoT, and using CBOR as the message-encoding format makes sense. @@ -57,6 +67,7 @@ The core COSE specification consists of two documents. contains the serialization structures and the procedures for using the different cryptographic algorithms. This document provides for an initial set of algorithms that are then use with those structures. + Additional algorithms beyond what are in this document are defined elsewhere. @@ -82,6 +93,14 @@ Authenticated Encryption with Authenticated Data (AEAD) algorithms provide the same content authentication service as AE algorithms, but they additionally provide for authentication of non-encrypted data as well. + +
+ + At the time that was initially published, the CBOR Data Definition Language (CDDL) had not yet been published. + This document uses a variant of CDDL which is described in + +
+
@@ -131,7 +150,7 @@ If the 'key_ops' field is present, it MUST include 'verify' when verifying an ECDSA signature.
The security strength of the signature is no greater than the minimum of the security strength associated with the bit length of the key and the security strength of the hash function. - Note: Use of this technique is a good idea even when good random number generation exists. Doing so both reduces the possibility of having the same value of 'k' in two signature operations and allows for reproducible signature values, which helps testing. + Note: Use of deterministic signatures is a good idea even when good random number generation exists. Doing so both reduces the possibility of having the same value of 'k' in two signature operations and allows for reproducible signature values, which helps testing. There are two substitution attacks that can theoretically be mounted against the ECDSA signature algorithm. Changing the curve used to validate the signature: If one changes the curve used to validate the signature, then potentially one could have two messages with the same signature, each computed under a different curve. The only requirement on the new curve is that its order be the same as the old one and it be acceptable to the client. An example would be to change from using the curve secp256r1 (aka P-256) to using secp256k1. (Both are 256-bit curves.) We currently do not have any way to deal with this version of the attack except to restrict the overall set of curves that can be used. @@ -175,7 +194,7 @@
HMAC was designed to deal with length extension attacks. The algorithm was also designed to allow for new hash algorithms to be directly plugged in without changes to the hash function. The HMAC design process has been shown as solid since, while the security of hash algorithms such as MD5 has decreased over time; the security of HMAC combined with MD5 has not yet been shown to be compromised . - The HMAC algorithm is parameterized by an inner and outer padding, a hash function (h), and an authentication tag value length. For this specification, the inner and outer padding are fixed to the values set in . The length of the authentication tag corresponds to the difficulty of producing a forgery. For use in constrained environments, we define a set of HMAC algorithms that are truncated. There are currently no known issues with truncation; however, the security strength of the message tag is correspondingly reduced in strength. When truncating, the leftmost tag length bits are kept and transmitted. + The HMAC algorithm is parameterized by an inner and outer padding, a hash function (h), and an authentication tag value length. For this specification, the inner and outer padding are fixed to the values set in . The length of the authentication tag corresponds to the difficulty of producing a forgery. For use in constrained environments, we define one HMAC algorithms that is truncated. There are currently no known issues with truncation; however, the security strength of the message tag is correspondingly reduced in strength. When truncating, the leftmost tag length bits are kept and transmitted. The algorithms defined in this document can be found in . Name @@ -265,7 +284,7 @@
- This docuement defines the identifier and usages for three content encryption algorithms. + This document defines the identifier and usages for three content encryption algorithms.
@@ -389,9 +408,9 @@
- ChaCha20 and Poly1305 combined together is an AEAD mode that is defined in . This is an algorithm defined to be a cipher that is not AES and thus would not suffer from any future weaknesses found in AES. These cryptographic functions are designed to be fast in software-only implementations. + ChaCha20 and Poly1305 combined together is an AEAD mode that is defined in . This is an algorithm defined to be a cipher that is not AES and thus would not suffer from any future weaknesses found in AES. These cryptographic functions are designed to be fast in software-only implementations. - The ChaCha20/Poly1305 AEAD construction defined in has no parameterization. It takes a 256-bit key and a 96-bit nonce, as well as the plaintext and additional data as inputs and produces the ciphertext as an option. We define one algorithm identifier for this algorithm in . + The ChaCha20/Poly1305 AEAD construction defined in has no parameterization. It takes a 256-bit key and a 96-bit nonce, as well as the plaintext and additional data as inputs and produces the ciphertext as an option. We define one algorithm identifier for this algorithm in . Name Value @@ -977,81 +996,19 @@ COSE_KDF_Context = [
-
- IANA has created a new registry titled "COSE Algorithms". The registry has been created to use the "Expert Review Required" registration procedure. Guidelines for the experts are provided in . It should be noted that, in addition to the expert review, some portions of the registry require a specification, potentially a Standards Track RFC, be supplied as well. - - - - - -A value that can be used to identify an algorithm in documents for easier comprehension. The name SHOULD be unique. However, the 'Value' field is what is used to identify the algorithm, not the 'name' field. -The value to be used to identify this algorithm. Algorithm values MUST be unique. The value can be a positive integer, a negative integer, or a string. Integer values between -256 and 255 and strings of length 1 are designated as "Standards Action". Integer values from -65536 to 65535 and strings of length 2 are designated as "Specification Required". Integer values greater than 65535 and strings of length greater than 2 are designated as "Expert Review". Integer values less than -65536 are marked as private use. - -A short description of the algorithm. -A document where the algorithm is defined (if publicly available). -Does the IETF have a consensus recommendation to use the algorithm? The legal values are 'Yes', 'No', and 'Deprecated'. - The initial contents of the registry can be found in Tables , , , , , , , , , , , and . All of the entries in the "References" column of this registry point to this document. All of the entries in the "Recommended" column are set to "Yes". - Additionally, the label of 0 is to be marked as 'Reserved'. - - NOTE: The assignment of algorithm identifiers in this document was done so that positive numbers were used for the first layer objects (COSE_Sign, COSE_Sign1, COSE_Encrypt, COSE_Encrypt0, COSE_Mac, and COSE_Mac0). Negative numbers were used for second layer objects (COSE_Signature and COSE_recipient). Expert reviewers should consider this practice, but are not expected to be restricted by this precedent. -
- - +
IANA has created a new registry titled "COSE Key Type Parameters". The registry has been created to use the "Expert Review Required" registration procedure. Expert review guidelines are provided in . @@ -1086,18 +1043,15 @@ COSE_KDF_Context = [
- IANA has created a new registry titled "COSE Elliptic Curves". The registry has been created to use the "Expert Review Required" registration procedure. Guidelines for the experts are provided in . It should be noted that, in addition to the expert review, some portions of the registry require a specification, potentially a Standards Track RFC, be supplied as well. - The columns of the table are: - - -This is a descriptive name that enables easier reference to the item. It is not used in the encoding. -This is the value used to identify the curve. These values MUST be unique. The integer values from -256 to 255 are designated as "Standards Action". The integer values from 256 to 65535 and -65536 to -257 are designated as "Specification Required". Integer values over 65535 are designated as "Expert Review". Integer values less than -65536 are marked as private use. + + IANA created and populated the "COSE Elliptic Curves" registry as part of processing . + IANA is requested to change the reference from to this document for all values in the registry. + -This designates the key type(s) that can be used with this curve. -This field contains a brief description of the curve. -This contains a pointer to the public specification for the curve if one exists. -Does the IETF have a consensus recommendation to use the algorithm? The legal values are 'Yes', 'No', and 'Deprecated'. - This registry has been initially populated by the values in . All of the entries in the "References" column of this registry point to this document. All of the entries in the "Recommended" column are set to "Yes". + + This document does not change the guidance for Designated Experts. + +
@@ -1111,7 +1065,7 @@ COSE_KDF_Context = [ Experts should take into account the expected usage of fields when approving point assignment. The fact that there is a range for standards track documents does not mean that a standards track document cannot have points assigned outside of that range. The length of the encoded value should be weighed against how many code points of that length are left, the size of device it will be used on, and the number of code points left that encode to that size. When algorithms are registered, vanity registrations should be discouraged. One way to do this is to require registrations to provide additional documentation on security analysis of the algorithm. Another thing that should be considered is requesting an opinion on the algorithm from the Crypto Forum Research Group (CFRG). Algorithms that do not meet the security requirements of the community and the messages structures should not be registered. -
+
@@ -1144,26 +1098,17 @@ COSE_KDF_Context = [ - - - COSE Struct - - - - - - - + - - + + - + @@ -1216,21 +1161,8 @@ COSE_KDF_Context = [ - - - -CBOR data definition language (CDDL): a notational convention to express CBOR data structures - - - - - - - -This document proposes a notational convention to express CBOR data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR. - - - + + - -
- -This example uses the following: - -MAC: AES-CMAC, 256-bit key, truncated to 64 bitsRecipient class: direct shared secret - -Size of binary file is 57 bytes - -
- -97( - [ - / protected / h'a1010f' / { - \ alg \ 1:15 \ AES-CBC-MAC-256//64 \ - } / , - / unprotected / {}, - / payload / 'This is the content.', - / tag / h'9e1226ba1f81b848', - / recipients / [ - [ - / protected / h'', - / unprotected / { - / alg / 1:-6 / direct /, - / kid / 4:'our-secret' - }, - / ciphertext / h'' - ] - ] - ] -) -
-
- -This example uses the following: -MAC: HMAC w/SHA-256, 256-bit key - -Recipient class: ECDH key agreement, two static keys, HKDF w/ context structure - -Size of binary file is 214 bytes -
- -97( - [ - / protected / h'a10105' / { - \ alg \ 1:5 \ HMAC 256//256 \ - } / , - / unprotected / {}, - / payload / 'This is the content.', - / tag / h'81a03448acd3d305376eaa11fb3fe416a955be2cbe7ec96f012c99 -4bc3f16a41', - / recipients / [ - [ - / protected / h'a101381a' / { - \ alg \ 1:-27 \ ECDH-SS + HKDF-256 \ - } / , - / unprotected / { - / static kid / -3:'peregrin.took@tuckborough.example', - / kid / 4:'meriadoc.brandybuck@buckland.example', - / U nonce / -22:h'4d8553e7e74f3c6a3a9dd3ef286a8195cbf8a23d -19558ccfec7d34b824f42d92bd06bd2c7f0271f0214e141fb779ae2856abf585a583 -68b017e7f2a9e5ce4db5' - }, - / ciphertext / h'' - ] - ] - ] -) -
- -
This example uses the following: - -MAC: AES-MAC, 128-bit key, truncated to 64 bits - -Recipient class: AES Key Wrap w/ a pre-shared 256-bit key - -Size of binary file is 109 bytes -
- -97( - [ - / protected / h'a1010e' / { - \ alg \ 1:14 \ AES-CBC-MAC-128//64 \ - } / , - / unprotected / {}, - / payload / 'This is the content.', - / tag / h'36f5afaf0bab5d43', - / recipients / [ - [ - / protected / h'', - / unprotected / { - / alg / 1:-5 / A256KW /, - / kid / 4:'018c0ae5-4d9b-471b-bfd6-eef314bc7037' - }, - / ciphertext / h'711ab0dc2fc4585dce27effa6781c8093eba906f227 -b6eb0' - ] - ] - ] -) -
- -
- -This example uses the following: - -MAC: HMAC w/ SHA-256, 128-bit key - -Recipient class: Uses three different methods - -ECDH Ephemeral-Static, Curve P-521, AES Key Wrap w/ 128-bit key - -AES Key Wrap w/ 256-bit key - -Size of binary file is 309 bytes -
- -97( - [ - / protected / h'a10105' / { - \ alg \ 1:5 \ HMAC 256//256 \ - } / , - / unprotected / {}, - / payload / 'This is the content.', - / tag / h'bf48235e809b5c42e995f2b7d5fa13620e7ed834e337f6aa43df16 -1e49e9323e', - / recipients / [ - [ - / protected / h'a101381c' / { - \ alg \ 1:-29 \ ECHD-ES+A128KW \ - } / , - / unprotected / { - / ephemeral / -1:{ - / kty / 1:2, - / crv / -1:3, - / x / -2:h'0043b12669acac3fd27898ffba0bcd2e6c366d53bc4db -71f909a759304acfb5e18cdc7ba0b13ff8c7636271a6924b1ac63c02688075b55ef2 -d613574e7dc242f79c3', - / y / -3:true - }, - / kid / 4:'bilbo.baggins@hobbiton.example' - }, - / ciphertext / h'339bc4f79984cdc6b3e6ce5f315a4c7d2b0ac466fce -a69e8c07dfbca5bb1f661bc5f8e0df9e3eff5' - ], - [ - / protected / h'', - / unprotected / { - / alg / 1:-5 / A256KW /, - / kid / 4:'018c0ae5-4d9b-471b-bfd6-eef314bc7037' - }, - / ciphertext / h'0b2c7cfce04e98276342d6476a7723c090dfdd15f9a -518e7736549e998370695e6d6a83b4ae507bb' - ] - ] - ] -) -
-
- -
-
-This example uses the following: -MAC: AES-CMAC, 256-bit key, truncated to 64 bits - -Recipient class: direct shared secret - -Size of binary file is 37 bytes -
- - -17( - [ - / protected / h'a1010f' / { - \ alg \ 1:15 \ AES-CBC-MAC-256//64 \ - } / , - / unprotected / {}, - / payload / 'This is the content.', - / tag / h'726043745027214f' - ] -) -
Note that this example uses the same inputs as .
-
- -
-
-This is an example of a COSE Key Set. This example includes the public keys for all of the previous examples. In order the keys are: -An EC key with a kid of "meriadoc.brandybuck@buckland.example"An EC key with a kid of "peregrin.took@tuckborough.example" - -An EC key with a kid of "bilbo.baggins@hobbiton.example"An EC key with a kid of "11" - -Size of binary file is 481 bytes - -
- - -[ - { - -1:1, - -2:h'65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de439c0 -8551d', - -3:h'1e52ed75701163f7f9e40ddf9f341b3dc9ba860af7e0ca7ca7e9eecd008 -4d19c', - 1:2, - 2:'meriadoc.brandybuck@buckland.example' - }, - { - -1:1, - -2:h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a -09eff', - -3:h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbf -c117e', - 1:2, - 2:'11' - }, - { - -1:3, - -2:h'0072992cb3ac08ecf3e5c63dedec0d51a8c1f79ef2f82f94f3c737bf5de -7986671eac625fe8257bbd0394644caaa3aaf8f27a4585fbbcad0f2457620085e5c8 -f42ad', - -3:h'01dca6947bce88bc5790485ac97427342bc35f887d86d65a089377e247e -60baa55e4e8501e2ada5724ac51d6909008033ebc10ac999b9d7f5cc2519f3fe1ea1 -d9475', - 1:2, - 2:'bilbo.baggins@hobbiton.example' - }, - { - -1:1, - -2:h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbfbf054e1c7b4d91 -d6280', - -3:h'f01400b089867804b8e9fc96c3932161f1934f4223069170d924b7e03bf -822bb', - 1:2, - 2:'peregrin.took@tuckborough.example' - } -] -
- -
This is an example of a COSE Key Set. This example includes the private keys for all of the previous examples. - -In order the keys are: An EC key with a kid of "meriadoc.brandybuck@buckland.example"A shared-secret key with a kid of "our-secret" - -An EC key with a kid of "peregrin.took@tuckborough.example" -A shared-secret key with a kid of "018c0ae5-4d9b-471b-bfd6-eef314bc7037" -An EC key with a kid of "bilbo.baggins@hobbiton.example"An EC key with a kid of "11" - -Size of binary file is 816 bytes -
- -[ - { - 1:2, - 2:'meriadoc.brandybuck@buckland.example', - -1:1, - -2:h'65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de439c0 -8551d', - -3:h'1e52ed75701163f7f9e40ddf9f341b3dc9ba860af7e0ca7ca7e9eecd008 -4d19c', - -4:h'aff907c99f9ad3aae6c4cdf21122bce2bd68b5283e6907154ad911840fa -208cf' - }, - { - 1:2, - 2:'11', - -1:1, - -2:h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a -09eff', - -3:h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbf -c117e', - -4:h'57c92077664146e876760c9520d054aa93c3afb04e306705db609030850 -7b4d3' - }, - { - 1:2, - 2:'bilbo.baggins@hobbiton.example', - -1:3, - -2:h'0072992cb3ac08ecf3e5c63dedec0d51a8c1f79ef2f82f94f3c737bf5de -7986671eac625fe8257bbd0394644caaa3aaf8f27a4585fbbcad0f2457620085e5c8 -f42ad', - -3:h'01dca6947bce88bc5790485ac97427342bc35f887d86d65a089377e247e -60baa55e4e8501e2ada5724ac51d6909008033ebc10ac999b9d7f5cc2519f3fe1ea1 -d9475', - -4:h'00085138ddabf5ca975f5860f91a08e91d6d5f9a76ad4018766a476680b -55cd339e8ab6c72b5facdb2a2a50ac25bd086647dd3e2e6e99e84ca2c3609fdf177f -eb26d' - }, - { - 1:4, - 2:'our-secret', - -1:h'849b57219dae48de646d07dbb533566e976686457c1491be3a76dcea6c4 -27188' - }, - { - 1:2, - -1:1, - 2:'peregrin.took@tuckborough.example', - -2:h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbfbf054e1c7b4d91 -d6280', - -3:h'f01400b089867804b8e9fc96c3932161f1934f4223069170d924b7e03bf -822bb', - -4:h'02d1f7e6f26c43d4868d87ceb2353161740aacf1f7163647984b522a848 -df1c3' - }, - { - 1:4, - 2:'our-secret2', - -1:h'849b5786457c1491be3a76dcea6c4271' - }, - { - 1:4, - 2:'018c0ae5-4d9b-471b-bfd6-eef314bc7037', - -1:h'849b57219dae48de646d07dbb533566e976686457c1491be3a76dcea6c4 -27188' - } -] -
-
diff --git a/draft-schaad-cose-rfc8152bis-struct.xml b/draft-schaad-cose-rfc8152bis-struct.xml index 8fd0c7f..d190adc 100644 --- a/draft-schaad-cose-rfc8152bis-struct.xml +++ b/draft-schaad-cose-rfc8152bis-struct.xml @@ -1,7 +1,7 @@ + ]> @@ -35,16 +35,57 @@ + + + + The source for this draft is being maintained in GitHub. + Suggested changes should be submitted as pull requests at . + Instructions are on that page as well. + Editorial changes can be managed in GitHub, but any substantial issues need to be discussed on the COSE mailing list. + +
- There has been an increased focus on small, constrained devices that make up the Internet of Things (IoT). One of the standards that has come out of this process is "Concise Binary Object Representation (CBOR)" . CBOR extended the data model of the JavaScript Object Notation (JSON) by allowing for binary data, among other changes. CBOR is being adopted by several of the IETF working groups dealing with the IoT world as their encoding of data structures. CBOR was designed specifically to be both small in terms of messages transport and implementation size and be a schema-free decoder. A need exists to provide message security services for IoT, and using CBOR as the message-encoding format makes sense. + There has been an increased focus on small, constrained devices that make up the Internet of Things (IoT). One of the standards that has come out of this process is "Concise Binary Object Representation (CBOR)" . CBOR extended the data model of the JavaScript Object Notation (JSON) by allowing for binary data, among other changes. CBOR has been adopted by several of the IETF working groups dealing with the IoT world as their encoding of data structures. CBOR was designed specifically to be both small in terms of messages transport and implementation size and be a schema-free decoder. A need exists to provide message security services for IoT, and using CBOR as the message-encoding format makes sense. - The JOSE working group produced a set of documents using JSON that specified how to process encryption, signatures, and Message Authentication Code (MAC) operations and how to encode keys using JSON. This document defines the CBOR Object Signing and Encryption (COSE) standard, which does the same thing for the CBOR encoding format. While there is a strong attempt to keep the flavor of the original JSON Object Signing and Encryption (JOSE) documents, two considerations are taken into account: + The JOSE working group produced a set of documents using JSON that specified how to process encryption, signatures, and Message Authentication Code (MAC) operations and how to encode keys using JSON. This document along with defines the CBOR Object Signing and Encryption (COSE) standard, which does the same thing for the CBOR encoding format. While there is a strong attempt to keep the flavor of the original JSON Object Signing and Encryption (JOSE) documents, two considerations are taken into account: CBOR has capabilities that are not present in JSON and are appropriate to use. One example of this is the fact that CBOR has a method of encoding binary directly without first converting it into a base64-encoded string. -COSE is not a direct copy of the JOSE specification. In the process of creating COSE, decisions that were made for JOSE were re-examined. In many cases, different results were decided on as the criteria were not always the same. + COSE is not a direct copy of the JOSE specification. In the process of creating COSE, decisions that were made for JOSE were re-examined. In many cases, different results were decided on as the criteria were not always the same. + + + This document contains: + + + The description of the structure for the CBOR objects which are transmitted over the wire. + Two objects are defined for encryption, signing and message authentication. + One object is defined for transporting keys and one for transporting groups of keys. + + + The procedures used to compute build the inputs to the cryptographic functions required for each of the structures. + + + A starting set of attributes that apply to the different security objects. + + + + + + This document does not contain the rules and procedures for using specific cryptographic algorithms. + Details on specific algorithms can be found in and . + Details for additional algorithms are expected to be defined in future documents. + + + + One feature that is present in CMS that is not present in this standard is a digest structure. + This omission is deliberate. + It is better for the structure to be defined in each document as different protocols will want to include a different set of fields as part of the structure. + While an algorithm identifier and the digesst value are going to be common to all applications, the two values may not always be adjacent as the algorithm could be defined once with multiple values. + Applications may additionally want to defined additional data fields as part of the stucture. + A common structure is going to include a URI or other pointer to where the data that is being hashed is kept, allowing this to be application specific. +
@@ -58,17 +99,24 @@
- The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL - NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", - "MAY", and "OPTIONAL" in this document are to be interpreted as - described in BCP 14 when, and only when, they - appear in all capitals, as shown here. - When the words appear in lowercase, this interpretation does not apply. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. +
- There is currently no standard CBOR grammar available for use by specifications. The CBOR structures are therefore described in prose. - The document was developed by first working on the grammar and then developing the prose to go with it. An artifact of this is that the prose was written using the primitive type strings defined by CBOR Data Definition Language (CDDL) . In this specification, the following primitive types are used: + + There was not a standard CBOR grammar available when COSE was originally written. + For that reason the CBOR structures defined here are described in prose. + Since that time CBOR Data Definition Language (CDDL) has been published as an RFC. + The CBOR grammar presented in this document is compatible with CDDL. + + + + The document was developed by first working on the grammar and then developing the prose to go with it. + An artifact of this is that the prose was written using the primitive type strings defined by CBOR Data Definition Language (CDDL) . + In this specification, the following primitive types are used: + any -- non-specific value that permits all CBOR values to be placed here. bool -- a boolean value (true: major type 7, value 21; false: major type 7, value 20). @@ -83,17 +131,20 @@ FOO / BAR -- indicates that either FOO or BAR can appear here. [+ FOO] -- indicates that the type FOO appears one or more times in an array. - As well as the prose description, a version of a CBOR grammar is presented in CDDL. Since CDDL has not been published in an RFC, this grammar may not work with the final version of CDDL. The CDDL grammar is informational; the prose description is normative. + + As well as the prose description, a version of a CBOR grammar is presented in CDDL. + The CDDL grammar is informational; the prose description is normative. + The collected CDDL can be extracted from the XML version of this document via the following XPath expression below. (Depending on the XPath evaluator one is using, it may be necessary to deal with > as an entity.) -
+
//artwork[@type='CDDL']/text()
CDDL expects the initial non-terminal symbol to be the first symbol in the file. For this reason, the first fragment of CDDL is presented here. -
- +
+ start = COSE_Messages / COSE_Key / COSE_KeySet / Internal_Types ; This is defined to make the tool quieter: @@ -106,16 +157,20 @@ Internal_Types = Sig_structure / Enc_structure / MAC_structure /
In JSON, maps are called objects and only have one kind of map key: a string. In COSE, we use strings, negative integers, and unsigned integers as map keys. The integers are used for compactness of encoding and easy comparison. The inclusion of strings allows for an additional range of short encoded values to be used as well. Since the word "key" is mainly used in its other meaning, as a cryptographic key, we use the term "label" for this usage as a map key. - The presence of a label in a COSE map that is not a string or an integer is an error. Applications can either fail processing or process messages with incorrect labels; however, they MUST NOT create messages with incorrect labels. + + The presence of a label in a COSE map that is not a string or an integer is an error. + Applications can either fail processing or process messages by ignoring incorrect labels; however, they MUST NOT create messages with incorrect labels. + A CDDL grammar fragment defines the non-terminal 'label', as in the previous paragraph, and 'values', which permits any value to be used. -
- +
+ label = int / tstr values = any
+
In this document, we use the following terminology: Byte is a synonym for octet. @@ -126,15 +181,27 @@ values = any Authenticated Encryption with Authenticated Data (AEAD) algorithms provide the same content authentication service as AE algorithms, but they additionally provide for authentication of non-encrypted data as well.
+
- The COSE object structure is designed so that there can be a large amount of common code when parsing and processing the different types of security messages. All of the message structures are built on the CBOR array type. The first three elements of the array always contain the same information: -The set of protected header parameters wrapped in a bstr. -The set of unprotected header parameters as a map. -The content of the message. The content is either the plaintext or the ciphertext as appropriate. The content may be detached, but the location is still used. The content is wrapped in a bstr when present and is a nil value when detached. - -Elements after this point are dependent on the specific message type. + + The COSE object structure is designed so that there can be a large amount of common code when parsing and processing the different types of security messages. + All of the message structures are built on the CBOR array type. + The first three elements of the array always contain the same information: + + The set of protected header parameters wrapped in a bstr. + The set of unprotected header parameters as a map. + + The content of the message. + The content is either the plaintext or the ciphertext as appropriate. + The content may be detached (i.e. transported separately from the COSE structure), but the location is still used. + The content is wrapped in a bstr when present and is a nil value when detached. + + + + Elements after this point are dependent on the specific message type. + - COSE messages are also built using the concept of layers to separate different types of cryptographic concepts. As an example of how this works, consider the COSE_Encrypt message (). This message type is broken into two layers: the content layer and the recipient layer. In the content layer, the plaintext is encrypted and information about the encrypted message is placed. In the recipient layer, the content encryption key (CEK) is encrypted and information about how it is encrypted for each recipient is placed. A single layer version of the encryption message COSE_Encrypt0 () is provided for cases where the CEK is pre-shared. + COSE messages are built using the concept of layers to separate different types of cryptographic concepts. As an example of how this works, consider the COSE_Encrypt message (). This message type is broken into two layers: the content layer and the recipient layer. In the content layer, the plaintext is encrypted and information about the encrypted message is placed. In the recipient layer, the content encryption key (CEK) is encrypted and information about how it is encrypted for each recipient is placed. A single layer version of the encryption message COSE_Encrypt0 () is provided for cases where the CEK is pre-shared. Identification of which type of message has been presented is done by the following methods: The specific message type is known from the context. This may be defined by a marker in the containing structure or by restrictions specified by the application protocol. @@ -143,7 +210,7 @@ Elements after this point are dependent on the specific message type. When a COSE object is carried in a media type of 'application/cose', the optional parameter 'cose-type' can be used to identify the embedded object. The parameter is OPTIONAL if the tagged version of the structure is used. The parameter is REQUIRED if the untagged version of the structure is used. The value to use with the parameter for each of the structures can be found in . When a COSE object is carried as a CoAP payload, the CoAP Content-Format Option can be used to identify the message content. The CoAP Content-Format values can be found in . The CBOR tag for the message structure is not required as each security message is uniquely identified. - + CBOR Tag cose-type Data Item @@ -174,9 +241,48 @@ Elements after this point are dependent on the specific message type. COSE Mac w/o Recipients Object + + Media Type + Encoding + ID + Reference + application/cose; cose-type="cose-sign" + + 98 + [RFC8152] + application/cose; cose-type="cose-sign1" + + 18 + [RFC8152] + application/cose; cose-type="cose-encrypt" + + 96 + [RFC8152] + application/cose; cose-type="cose-encrypt0" + + 16 + [RFC8152] + application/cose; cose-type="cose-mac" + + 97 + [RFC8152] + application/cose; cose-type="cose-mac0" + + 17 + [RFC8152] + application/cose-key + + 101 + [RFC8152] + application/cose-key-set + + 102 + [RFC8152] + + The following CDDL fragment identifies all of the top messages defined in this document. Separate non-terminals are defined for the tagged and the untagged versions of the messages. -
- +
+ COSE_Messages = COSE_Untagged_Message / COSE_Tagged_Message COSE_Untagged_Message = COSE_Sign / COSE_Sign1 / @@ -193,18 +299,35 @@ COSE_Tagged_Message = COSE_Sign_Tagged / COSE_Sign1_Tagged /
The structure of COSE has been designed to have two buckets of information that are not considered to be part of the payload itself, but are used for holding information about content, algorithms, keys, or evaluation hints for the processing of the layer. These two buckets are available for use in all of the structures except for keys. While these buckets are present, they may not all be usable in all instances. For example, while the protected bucket is defined as part of the recipient structure, some of the algorithms used for recipient structures do not provide for authenticated data. If this is the case, the protected bucket is left empty. Both buckets are implemented as CBOR maps. The map key is a 'label' (). The value portion is dependent on the definition for the label. Both maps use the same set of label/value pairs. The integer and string values for labels have been divided into several sections including a standard range, a private range, and a range that is dependent on the algorithm selected. The defined labels can be found in the "COSE Header Parameters" IANA registry (). - Two buckets are provided for each layer: -Contains parameters about the current layer that are to be cryptographically protected. This bucket MUST be empty if it is not going to be included in a cryptographic computation. This bucket is encoded in the message as a binary object. This value is obtained by CBOR encoding the protected map and wrapping it in a bstr object. Senders SHOULD encode a zero-length map as a zero-length string rather than as a zero-length map (encoded as h'a0'). The zero-length binary encoding is preferred because it is both shorter and the version used in the serialization structures for cryptographic computation. After encoding the map, the value is wrapped in the binary object. Recipients MUST accept both a zero-length binary value and a zero-length map encoded in the binary value. The wrapping allows for the encoding of the protected map to be transported with a greater chance that it will not be altered in transit. (Badly behaved intermediates could decode and re-encode, but this will result in a failure to verify unless the re-encoded byte string is identical to the decoded byte string.) This avoids the problem of all parties needing to be able to do a common canonical encoding. - -Contains parameters about the current layer that are not cryptographically protected. Only parameters that deal with the current layer are to be placed at that layer. As an example of this, the parameter 'content type' describes the content of the message being carried in the message. As such, this parameter is placed only in the content layer and is not placed in the recipient or signature layers. In principle, one should be able to process any given layer without reference to any other layer. With the exception of the COSE_Sign structure, the only data that needs to cross layers is the cryptographic key. + + Two buckets are provided for each layer: + + + Contains parameters about the current layer that are cryptographically protected. + This bucket MUST be empty if it is not going to be included in a cryptographic computation. + This bucket is encoded in the message as a binary object. + This value is obtained by CBOR encoding the protected map and wrapping it in a bstr object. + Senders SHOULD encode a zero-length map as a zero-length byte string rather than as a zero-length map (encoded as h'a0'). + The zero-length binary encoding is preferred because it is both shorter and the version used in the serialization structures for cryptographic computation. + After encoding the map, the value is wrapped in the binary object. + Recipients MUST accept both a zero-length binary value and a zero-length map encoded in the binary value. + The wrapping allows for the encoding of the protected map to be transported with a greater chance that it will not be altered in transit. + (Badly behaved intermediates could decode and re-encode, but this will result in a failure to verify unless the re-encoded byte string is identical to the decoded byte string.) + This avoids the problem of all parties needing to be able to do a common canonical encoding. + + + Contains parameters about the current layer that are not cryptographically protected. + + Only parameters that deal with the current layer are to be placed at that layer. As an example of this, the parameter 'content type' describes the content of the message being carried in the message. As such, this parameter is placed only in the content layer and is not placed in the recipient or signature layers. In principle, one should be able to process any given layer without reference to any other layer. With the exception of the COSE_Sign structure, the only data that needs to cross layers is the cryptographic key. + The buckets are present in all of the security objects defined in this document. The fields in order are the 'protected' bucket (as a CBOR 'bstr' type) and then the 'unprotected' bucket (as a CBOR 'map' type). The presence of both buckets is required. The parameters that go into the buckets come from the IANA "COSE Header Parameters" registry (). Some common parameters are defined in the next section, but a number of parameters are defined throughout this document. Labels in each of the maps MUST be unique. When processing messages, if a label appears multiple times, the message MUST be rejected as malformed. Applications SHOULD verify that the same label does not occur in both the protected and unprotected headers. If the message is not rejected as malformed, attributes MUST be obtained from the protected bucket before they are obtained from the unprotected bucket. The following CDDL fragment represents the two header buckets. A group "Headers" is defined in CDDL that represents the two buckets in which attributes are placed. This group is used to provide these two fields consistently in all locations. A type is also defined that represents the map of common headers. -
- +
+ Headers = ( protected : empty_or_serialized_map, unprotected : header_map @@ -223,7 +346,7 @@ empty_or_serialized_map = bstr .cbor header_map / bstr .size 0 This section defines a set of common header parameters. A summary of these parameters can be found in . This table should be consulted to determine the value of label and the type of the value. The set of header parameters defined in this section are: - This parameter is used to indicate the algorithm used for the security processing. This parameter MUST be authenticated where the ability to do so exists. This support is provided by AEAD algorithms or construction (COSE_Sign, COSE_Sign0, COSE_Mac, and COSE_Mac0). This authentication can be done either by placing the header in the protected header bucket or as part of the externally supplied data. The value is taken from the "COSE Algorithms" registry (see ). + This parameter is used to indicate the algorithm used for the security processing. This parameter MUST be authenticated where the ability to do so exists. This support is provided by AEAD algorithms or construction (COSE_Sign, COSE_Sign0, COSE_Mac, and COSE_Mac0). This authentication can be done either by placing the parameter in the protected header bucket or as part of the externally supplied data. The value is taken from the "COSE Algorithms" registry (see ). The parameter is used to indicate which protected header labels an application that is processing a message is required to understand. Parameters defined in this document do not need to be included as they should be understood by all implementations. When present, this parameter MUST be placed in the protected header bucket. The array MUST have at least one value in it. @@ -255,7 +378,7 @@ empty_or_serialized_map = bstr .cbor header_map / bstr .size 0 This parameter holds one or more counter signature values. Counter signatures provide a method of having a second party sign some data. The counter signature parameter can occur as an unprotected attribute in any of the following structures: COSE_Sign1, COSE_Signature, COSE_Encrypt, COSE_recipient, COSE_Encrypt0, COSE_Mac, and COSE_Mac0. These structures all have the same beginning elements, so that a consistent calculation of the counter signature can be computed. Details on computing counter signatures are found in . - + Name Label Value Type @@ -300,8 +423,8 @@ empty_or_serialized_map = bstr .cbor header_map / bstr .size 0 The CDDL fragment that represents the set of headers defined in this section is given below. Each of the headers is tagged as optional because they do not need to be in every map; headers required in specific maps are discussed above. -
- +
+ Generic_Headers = ( ? 1 => int / tstr, ; algorithm identifier ? 2 => [+label], ; criticality @@ -329,8 +452,8 @@ For example, the COSE_Sign structure might include signatures generated with the The signature structure can be encoded as either tagged or untagged depending on the context it will be used in. A tagged COSE_Sign structure is identified by the CBOR tag 98. The CDDL fragment that represents this is: -
- +
+ COSE_Sign_Tagged = #6.98(COSE_Sign)
@@ -346,8 +469,8 @@ COSE_Sign_Tagged = #6.98(COSE_Sign) Note: When a signature with a message recovery algorithm is used (), the maximum number of bytes that can be recovered is the length of the payload. The size of the payload is reduced by the number of bytes that will be recovered. If all of the bytes of the payload are consumed, then the payload is encoded as a zero-length binary string rather than as being absent. This field is an array of signatures. Each signature is represented as a COSE_Signature structure. The CDDL fragment that represents the above text for COSE_Sign follows. -
- +
+ COSE_Sign = [ Headers, payload : bstr / nil, @@ -362,8 +485,8 @@ COSE_Sign = [ This field contains the computed signature value. The type of the field is a bstr. Algorithms MUST specify padding if the signature value is not a multiple of 8 bits. The CDDL fragment that represents the above text for COSE_Signature follows. -
- +
+ COSE_Signature = [ Headers, signature : bstr @@ -374,8 +497,8 @@ COSE_Signature = [
The COSE_Sign1 signature structure is used when only one signature is going to be placed on a message. The parameters dealing with the content and the signature are placed in the same pair of buckets rather than having the separation of COSE_Sign. The structure can be encoded as either tagged or untagged depending on the context it will be used in. A tagged COSE_Sign1 structure is identified by the CBOR tag 18. The CDDL fragment that represents this is: -
- +
+ COSE_Sign1_Tagged = #6.18(COSE_Sign1)
@@ -387,8 +510,8 @@ COSE_Sign1_Tagged = #6.18(COSE_Sign1) This is as described in . This field contains the computed signature value. The type of the field is a bstr. The CDDL fragment that represents the above text for COSE_Sign1 follows. -
- +
+ COSE_Sign1 = [ Headers, payload : bstr / nil, @@ -398,34 +521,65 @@ COSE_Sign1 = [
- One of the features offered in the COSE document is the ability for applications to provide additional data to be authenticated, but that is not carried as part of the COSE object. The primary reason for supporting this can be seen by looking at the CoAP message structure , where the facility exists for options to be carried before the payload. Examples of data that can be placed in this location would be the CoAP code or CoAP options. If the data is in the header section, then it is available for proxies to help in performing its operations. For example, the Accept Option can be used by a proxy to determine if an appropriate value is in the proxy's cache. But the sender can prevent a proxy from changing the set of values that it will accept by including that value in the resulting authentication tag. However, it may also be desired to protect these values so that if they are modified in transit, it can be detected. - - This document describes the process for using a byte array of externally supplied authenticated data; however, the method of constructing the byte array is a function of the application. Applications that use this feature need to define how the externally supplied authenticated data is to be constructed. Such a construction needs to take into account the following issues: - + + One of the features offered in the COSE document is the ability for applications to provide additional data to be authenticated, but that is not carried as part of the COSE object. + The primary reason for supporting this can be seen by looking at the CoAP message structure , where the facility exists for options to be carried before the payload. + Examples of data that can be placed in this location would be the CoAP code or CoAP options. + If the data is in the header section, then it is available for proxies to help in performing its operations. + For example, the Accept Option can be used by a proxy to determine if an appropriate value is in the proxy's cache. + But the sender can cause a failure at the server if a proxy, or an attacker, changes the set of accept values by including the field in the application supplied data. + -If multiple items are included, applications need to ensure that the same byte string is not produced if there are different inputs. This could occur by appending the strings 'AB' and 'CDE' or by appending the strings 'ABC' and 'DE'. This is usually addressed by making fields a fixed width and/or encoding the length of the field as part of the output. Using options from CoAP as an example, these fields use a TLV structure so they can be concatenated without any problems. + + This document describes the process for using a byte array of externally supplied authenticated data; the method of constructing the byte array is a function of the application. + Applications that use this feature need to define how the externally supplied authenticated data is to be constructed. Such a construction needs to take into account the following issues: + + + + If multiple items are included, applications need to ensure that the same byte string cannot produced if there are different inputs. + This could occur by appending the strings 'AB' and 'CDE' or by appending the strings 'ABC' and 'DE'. + This is usually addressed by making fields a fixed width and/or encoding the length of the field as part of the output. + Using options from CoAP as an example, these fields use a TLV structure so they can be concatenated without any problems. + -If multiple items are included, an order for the items needs to be defined. Using options from CoAP as an example, an application could state that the fields are to be ordered by the option number. + If multiple items are included, an order for the items needs to be defined. Using options from CoAP as an example, an application could state that the fields are to be ordered by the option number. -Applications need to ensure that the byte stream is going to be the same on both sides. Using options from CoAP might give a problem if the same relative numbering is kept. An intermediate node could insert or remove an option, changing how the relative number is done. An application would need to specify that the relative number must be re-encoded to be relative only to the options that are in the external data. + + Applications need to ensure that the byte string is going to be the same on both sides. + Using options from CoAP might give a problem if the same relative numbering is kept. + An intermediate node could insert or remove an option, changing how the relative number is done. + An application would need to specify that the relative number must be re-encoded to be relative only to the options that are in the external data. + + +
- In order to create a signature, a well-defined byte stream is needed. The Sig_struture is used to create the canonical form. This signing and verification process takes in the body information (COSE_Sign or COSE_Sign1), the signer information (COSE_Signature), and the application data (external source). A Sig_structure is a CBOR array. The fields of the Sig_struture in order are: - -A text string identifying the context of the signature. The context string is: - -"Signature" for signatures using the COSE_Signature structure. -"Signature1" for signatures using the COSE_Sign1 structure. -"CounterSignature" for signatures used as counter signature attributes. -The protected attributes from the body structure encoded in a bstr type. If there are no protected attributes, a bstr of length zero is used. - -The protected attributes from the signer structure encoded in a bstr type. If there are no protected attributes, a bstr of length zero is used. This field is omitted for the COSE_Sign1 signature structure. -The protected attributes from the application encoded in a bstr type. If this field is not supplied, it defaults to a zero-length binary string. (See for application guidance on constructing this field.) -The payload to be signed encoded in a bstr type. The payload is placed here independent of how it is transported. + + In order to create a signature, a well-defined byte string is needed. + The Sig_struture is used to create the canonical form. + This signing and verification process takes in the body information (COSE_Sign or COSE_Sign1), the signer information (COSE_Signature), and the application data (external source). + A Sig_structure is a CBOR array. + The fields of the Sig_struture in order are: + + + A text string identifying the context of the signature. The context string is: + + "Signature" for signatures using the COSE_Signature structure. + "Signature1" for signatures using the COSE_Sign1 structure. + "CounterSignature" for signatures used as counter signature attributes. + + + The protected attributes from the body structure encoded in a bstr type. If there are no protected attributes, a bstr of length zero is used. + + The protected attributes from the signer structure encoded in a bstr type. If there are no protected attributes, a bstr of length zero is used. This field is omitted for the COSE_Sign1 signature structure. + The protected attributes from the application encoded in a bstr type. If this field is not supplied, it defaults to a zero-length binary string. (See for application guidance on constructing this field.) + The payload to be signed encoded in a bstr type. The payload is placed here independent of how it is transported. + + The CDDL fragment that describes the above text is: -
- +
+ Sig_structure = [ context : "Signature" / "Signature1" / "CounterSignature", body_protected : empty_or_serialized_map, @@ -449,28 +603,48 @@ Sig_structure = [ Create the value ToBeSigned by encoding the Sig_structure to a byte string, using the encoding described in . Call the signature verification algorithm passing in K (the key to verify with), alg (the algorithm used sign with), ToBeSigned (the value to sign), and sig (the signature to be verified). - In addition to performing the signature verification, the application may also perform the appropriate checks to ensure that the key is correctly paired with the signing identity and that the signing identity is authorized before performing actions. + + In addition to performing the signature verification, the application performs the appropriate checks to ensure that the key is correctly paired with the signing identity and that the signing identity is authorized before performing actions. +
+
- Counter signatures provide a method of associating a different signature generated by different signers with some piece of content. This is normally used to provide a signature on a signature allowing for a proof that a signature existed at a given time (i.e., a Timestamp). In this document, we allow for counter signatures to exist in a greater number of environments. As an example, it is possible to place a counter signature in the unprotected attributes of a COSE_Encrypt object. This would allow for an intermediary to either verify that the encrypted byte stream has not been modified, without being able to decrypt it, or assert that an encrypted byte stream either existed at a given time or passed through it in terms of routing (i.e., a proxy signature). + + Counter signatures provide a method of associating a different signature generated by different signers with some piece of content. + This is normally used to provide a signature on a signature allowing for a proof that a signature existed at a given time (e.g., a Timestamp). + In this document, we allow for counter signatures to exist in a greater number of environments. + As an example, it is possible to place a counter signature in the unprotected attributes of a COSE_Encrypt object. + This would allow for an intermediary to either verify that the encrypted byte string has not been modified, without being able to decrypt it, or assert that an encrypted byte string either existed at a given time or passed through it in terms of routing (e.g., a proxy signature). + An example of a counter signature on a signature can be found in . An example of a counter signature in an encryption object can be found in . - The creation and validation of counter signatures over the different items relies on the fact that the objects have the same structure. The elements are a set of protected attributes, a set of unprotected attributes, and a body, in that order. This means that the Sig_structure can be used in a uniform manner to get the byte stream for processing a signature. If the counter signature is going to be computed over a COSE_Encrypt structure, the body_protected and payload items can be mapped into the Sig_structure in the same manner as from the COSE_Sign structure. + The creation and validation of counter signatures over the different items relies on the fact that the objects have the same structure. The elements are a set of protected attributes, a set of unprotected attributes, and a body, in that order. This means that the Sig_structure can be used in a uniform manner to get the byte string for processing a signature. If the counter signature is going to be computed over a COSE_Encrypt structure, the body_protected and payload items can be mapped into the Sig_structure in the same manner as from the COSE_Sign structure. It should be noted that only a signature algorithm with appendix (see ) can be used for counter signatures. This is because the body should be able to be processed without having to evaluate the counter signature, and this is not possible for signature schemes with message recovery.
+
- COSE supports two different encryption structures. COSE_Encrypt0 is used when a recipient structure is not needed because the key to be used is known implicitly. COSE_Encrypt is used the rest of the time. This includes cases where there are multiple recipients or a recipient algorithm other than direct is used. + + COSE supports two different encryption structures. + COSE_Encrypt0 is used when a recipient structure is not needed because the key to be used is known implicitly. + COSE_Encrypt is used the rest of the time. + This includes cases where there are multiple recipients or a recipient algorithm other than direct (i.e. pre-shared secret) is used. + +
The enveloped structure allows for one or more recipients of a message. There are provisions for parameters about the content and parameters about the recipient information to be carried in the message. The protected parameters associated with the content are authenticated by the content encryption algorithm. The protected parameters associated with the recipient are authenticated by the recipient algorithm (when the algorithm supports it). Examples of parameters about the content are the type of the content and the content encryption algorithm. Examples of parameters about the recipient are the recipient's key identifier and the recipient's encryption algorithm. - The same techniques and structures are used for encrypting both the plaintext and the keys. This is different from the approach used by both "Cryptographic Message Syntax (CMS)" and "JSON Web Encryption (JWE)" where different structures are used for the content layer and for the recipient layer. Two structures are defined: COSE_Encrypt to hold the encrypted content and COSE_recipient to hold the encrypted keys for recipients. + + The same techniques and nearly the same structure is used for encrypting both the plaintext and the keys. + This is different from the approach used by both "Cryptographic Message Syntax (CMS)" and "JSON Web Encryption (JWE)" where different structures are used for the content layer and for the recipient layer. + Two structures are defined: COSE_Encrypt to hold the encrypted content and COSE_recipient to hold the encrypted keys for recipients. -Examples of encrypted messages can be found in . + Examples of encrypted messages can be found in . + The COSE_Encrypt structure can be encoded as either tagged or untagged depending on the context it will be used in. A tagged COSE_Encrypt structure is identified by the CBOR tag 96. The CDDL fragment that represents this is: -
- +
+ COSE_Encrypt_Tagged = #6.96(COSE_Encrypt)
@@ -481,8 +655,8 @@ COSE_Encrypt_Tagged = #6.96(COSE_Encrypt) This field contains an array of recipient information structures. The type for the recipient information structure is a COSE_recipient. The CDDL fragment that corresponds to the above text is: -
- +
+ COSE_Encrypt = [ Headers, ciphertext : bstr / nil, @@ -500,8 +674,8 @@ COSE_Encrypt = [ This field contains an array of recipient information structures. The type for the recipient information structure is a COSE_recipient (an example of this can be found in ). If there are no recipient information structures, this element is absent. The CDDL fragment that corresponds to the above text for COSE_recipient is: -
- +
+ COSE_recipient = [ Headers, ciphertext : bstr / nil, @@ -524,8 +698,8 @@ COSE_recipient = [ Examples of encrypted messages can be found in . The COSE_Encrypt0 structure can be encoded as either tagged or untagged depending on the context it will be used in. A tagged COSE_Encrypt0 structure is identified by the CBOR tag 16. The CDDL fragment that represents this is: -
- +
+ COSE_Encrypt0_Tagged = #6.16(COSE_Encrypt0)
@@ -536,8 +710,8 @@ COSE_Encrypt0_Tagged = #6.16(COSE_Encrypt0) This is as described in . This is as described in . The CDDL fragment for COSE_Encrypt0 that corresponds to the above text is: -
- +
+ COSE_Encrypt0 = [ Headers, ciphertext : bstr / nil, @@ -546,7 +720,7 @@ COSE_Encrypt0 = [
- The encryption algorithm for AEAD algorithms is fairly simple. The first step is to create a consistent byte stream for the authenticated data structure. For this purpose, we use an Enc_structure. The Enc_structure is a CBOR array. The fields of the Enc_structure in order are: + The encryption algorithm for AEAD algorithms is fairly simple. The first step is to create a consistent byte string for the authenticated data structure. For this purpose, we use an Enc_structure. The Enc_structure is a CBOR array. The fields of the Enc_structure in order are: A text string identifying the context of the authenticated data structure. The context string is: @@ -560,8 +734,8 @@ COSE_Encrypt0 = [ The protected attributes from the body structure encoded in a bstr type. If there are no protected attributes, a bstr of length zero is used. The protected attributes from the application encoded in a bstr type. If this field is not supplied, it defaults to a zero-length bstr. (See for application guidance on constructing this field.) The CDDL fragment that describes the above text is: -
- +
+ Enc_structure = [ context : "Encrypt" / "Encrypt0" / "Enc_Recipient" / "Mac_Recipient" / "Rec_Recipient", @@ -574,23 +748,32 @@ Enc_structure = [ Create an Enc_structure and populate it with the appropriate fields. -Encode the Enc_structure to a byte stream (Additional Authenticated Data (AAD)), using the encoding described in . +Encode the Enc_structure to a byte string (Additional Authenticated Data (AAD)), using the encoding described in . Determine the encryption key (K). This step is dependent on the class of recipient algorithm being used. For: The key to be used is determined by the algorithm and key at the current layer. Examples are key transport keys (), key wrap keys (), or pre-shared secrets. -The key is determined by the key and algorithm in the recipient structure. The encryption algorithm and size of the key to be used are inputs into the KDF used for the recipient. (For direct, the KDF can be thought of as the identity operation.) Examples of these algorithms are found in Sections !!! DIRECT-KDF !!! and !!! ECDH !!! + + The key is determined by the key and algorithm in the recipient structure. + The encryption algorithm and size of the key to be used are inputs into the KDF used for the recipient. + (For direct, the KDF can be thought of as the identity operation.) + Examples of these algorithms are found in Sections !!! DIRECT-KDF !!! and !!! ECDH !!! of . + The key is randomly or pseudorandomly generated. Call the encryption algorithm with K (the encryption key), P (the plaintext), and AAD. Place the returned ciphertext into the 'ciphertext' field of the structure. For recipients of the message, recursively perform the encryption algorithm for that recipient, using K (the encryption key) as the plaintext. How to decrypt a message: Create an Enc_structure and populate it with the appropriate fields. -Encode the Enc_structure to a byte stream (AAD), using the encoding described in . +Encode the Enc_structure to a byte string (AAD), using the encoding described in . Determine the decryption key. This step is dependent on the class of recipient algorithm being used. For: The key to be used is determined by the algorithm and key at the current layer. Examples are key transport keys (), key wrap keys (), or pre-shared secrets. -The key is determined by the key and algorithm in the recipient structure. The encryption algorithm and size of the key to be used are inputs into the KDF used for the recipient. (For direct, the KDF can be thought of as the identity operation.) Examples of these algorithms are found in Sections !!! DIRECT-KDF !!! and !!! ECDH !!! . + + The key is determined by the key and algorithm in the recipient structure. + The encryption algorithm and size of the key to be used are inputs into the KDF used for the recipient. + (For direct, the KDF can be thought of as the identity operation.) + The key is determined by decoding and decrypting one of the recipient structures. Call the decryption algorithm with K (the decryption key to use), C (the ciphertext), and AAD. @@ -627,8 +810,8 @@ Enc_structure = [
The multiple recipient MACed message uses two structures: the COSE_Mac structure defined in this section for carrying the body and the COSE_recipient structure () to hold the key used for the MAC computation. Examples of MACed messages can be found in . The MAC structure can be encoded as either tagged or untagged depending on the context it will be used in. A tagged COSE_Mac structure is identified by the CBOR tag 97. The CDDL fragment that represents this is: -
- +
+ COSE_Mac_Tagged = #6.97(COSE_Mac)
@@ -640,8 +823,8 @@ COSE_Mac_Tagged = #6.97(COSE_Mac) This field contains the MAC value. This is as described in . The CDDL fragment that represents the above text for COSE_Mac follows. -
- +
+ COSE_Mac = [ Headers, payload : bstr / nil, @@ -655,9 +838,8 @@ COSE_Mac = [ In this section, we describe the structure and methods to be used when doing MAC authentication for those cases where the recipient is implicitly known. The MACed message uses the COSE_Mac0 structure defined in this section for carrying the body. Examples of MACed messages with an implicit key can be found in . The MAC structure can be encoded as either tagged or untagged depending on the context it will be used in. A tagged COSE_Mac0 structure is identified by the CBOR tag 17. The CDDL fragment that represents this is: -
- - +
+ COSE_Mac0_Tagged = #6.17(COSE_Mac0)
@@ -667,8 +849,8 @@ COSE_Mac0_Tagged = #6.17(COSE_Mac0) This is as described in . This field contains the MAC value. The CDDL fragment that corresponds to the above text is: -
- +
+ COSE_Mac0 = [ Headers, payload : bstr / nil, @@ -688,8 +870,8 @@ COSE_Mac0 = [ The payload to be MACed encoded in a bstr type. The payload is placed here independent of how it is transported. The CDDL fragment that corresponds to the above text is: -
- +
+ MAC_structure = [ context : "MAC" / "MAC0", protected : empty_or_serialized_map, @@ -698,30 +880,45 @@ MAC_structure = [ ]
- The steps to compute a MAC are: Create a MAC_structure and populate it with the appropriate fields. + + The steps to compute a MAC are: + + Create a MAC_structure and populate it with the appropriate fields. -Create the value ToBeMaced by encoding the MAC_structure to a byte stream, using the encoding described in . + Create the value ToBeMaced by encoding the MAC_structure to a byte string, using the encoding described in . -Call the MAC creation algorithm passing in K (the key to use), alg (the algorithm to MAC with), and ToBeMaced (the value to compute the MAC on). -Place the resulting MAC in the 'tag' field of the COSE_Mac or COSE_Mac0 structure. Encrypt and encode the MAC key for each recipient of the message. - The steps to verify a MAC are: Create a MAC_structure object and populate it with the appropriate fields. + Call the MAC creation algorithm passing in K (the key to use), alg (the algorithm to MAC with), and ToBeMaced (the value to compute the MAC on). + Place the resulting MAC in the 'tag' field of the COSE_Mac or COSE_Mac0 structure. + + For COSE_Mac structures, encrypt and encode the MAC key for each recipient of the message. + + + + + The steps to verify a MAC are: + + Create a MAC_structure object and populate it with the appropriate fields. -Create the value ToBeMaced by encoding the MAC_structure to a byte stream, using the encoding described in . -Obtain the cryptographic key from one of the recipients of the message. -Call the MAC creation algorithm passing in K (the key to use), alg (the algorithm to MAC with), and ToBeMaced (the value to compute the MAC on). -Compare the MAC value to the 'tag' field of the COSE_Mac or COSE_Mac0 structure. + Create the value ToBeMaced by encoding the MAC_structure to a byte string, using the encoding described in . + + For COSE_Mac structures, obtain the cryptographic key from one of the recipients of the message. + + Call the MAC creation algorithm passing in K (the key to use), alg (the algorithm to MAC with), and ToBeMaced (the value to compute the MAC on). + Compare the MAC value to the 'tag' field of the COSE_Mac or COSE_Mac0 structure. + +
- A COSE Key structure is built on a CBOR map object. The set of common parameters that can appear in a COSE Key can be found in the IANA "COSE Key Common Parameters" registry (). Additional parameters defined for specific key types can be found in the IANA "COSE Key Type Parameters" registry (). + A COSE Key structure is built on a CBOR map object. The set of common parameters that can appear in a COSE Key can be found in the IANA "COSE Key Common Parameters" registry (). Additional parameters defined for specific key types can be found in the IANA "COSE Key Type Parameters" registry (). A COSE Key Set uses a CBOR array object as its underlying type. The values of the array elements are COSE Keys. A COSE Key Set MUST have at least one element in the array. Examples of COSE Key Sets can be found in . Each element in a COSE Key Set MUST be processed independently. If one element in a COSE Key Set is either malformed or uses a key that is not understood by an application, that key is ignored and the other keys are processed normally. The element "kty" is a required element in a COSE_Key map. The CDDL grammar describing COSE_Key and COSE_KeySet is: -
- +
+ COSE_Key = { 1 => tstr / int, ; kty ? 2 => bstr, ; kid @@ -738,7 +935,7 @@ COSE_KeySet = [+COSE_Key] This document defines a set of common parameters for a COSE Key object. provides a summary of the parameters defined in this section. There are also parameters that are defined for specific key types. Key-type-specific parameters can be found in . - + Name Label CBOR Type @@ -747,7 +944,7 @@ COSE_KeySet = [+COSE_Key] kty 1 tstr / int - COSE Key Common Parameters + COSE Key Types Identification of the key type kid @@ -776,7 +973,7 @@ COSE_KeySet = [+COSE_Key] - This parameter is used to identify the family of keys for this structure and, thus, the set of key-type-specific parameters to be found. The set of values defined in this document can be found in !!!! TABLE_KEY_TYPES !!! . This parameter MUST be present in a key object. Implementations MUST verify that the key type is appropriate for the algorithm being processed. The key type MUST be included as part of the trust decision process. + This parameter is used to identify the family of keys for this structure and, thus, the set of key-type-specific parameters to be found. The set of values defined in this document can be found in . This parameter MUST be present in a key object. Implementations MUST verify that the key type is appropriate for the algorithm being processed. The key type MUST be included as part of the trust decision process. This parameter is used to restrict the algorithm that is used with the key. If this parameter is present in the key structure, the application MUST verify that this algorithm matches the algorithm for which the key is being used. If the algorithms do not match, then this key object MUST NOT be used to perform the cryptographic operation. Note that the same key can be in a different key structure with a different or no algorithm specified; however, this is considered to be a poor security practice. @@ -788,7 +985,7 @@ COSE_KeySet = [+COSE_Key] Extreme care needs to be taken when using a Base IV in an application. Many encryption algorithms lose security if the same IV is used twice. If different keys are derived for each sender, using the same Base IV with Partial IVs starting at zero is likely to ensure that the IV would not be used twice for a single key. If different keys are derived for each sender, starting at the same Base IV is likely to satisfy this condition. If the same key is used for multiple senders, then the application needs to provide for a method of dividing the IV space up between the senders. This could be done by providing a different base point to start from or a different Partial IV to start with and restricting the number of messages to be sent before rekeying. - + Name Value Description @@ -827,37 +1024,37 @@ COSE_KeySet = [+COSE_Key]
-
+
There are two signature algorithm schemes. The first is signature with appendix. In this scheme, the message content is processed and a signature is produced; the signature is called the appendix. This is the scheme used by algorithms such as ECDSA and the RSA Probabilistic Signature Scheme (RSASSA-PSS). (In fact, the SSA in RSASSA-PSS stands for Signature Scheme with Appendix.) The signature functions for this scheme are: -
- - signature = Sign(message content, key) +
+ +signature = Sign(message content, key) - valid = Verification(message content, key, signature) +valid = Verification(message content, key, signature)
- The second scheme is signature with message recovery (an example of such an algorithm is ). In this scheme, the message content is processed, but part of it is included in the signature. Moving bytes of the message content into the signature allows for smaller signatures; the signature size is still potentially large, but the message content has shrunk. This has implications for systems implementing these algorithms and for applications that use them. The first is that the message content is not fully available until after a signature has been validated. Until that point, the part of the message contained inside of the signature is unrecoverable. The second is that the security analysis of the strength of the signature is very much based on the structure of the message content. Messages that are highly predictable require additional randomness to be supplied as part of the signature process. In the worst case, it becomes the same as doing a signature with appendix. Finally, in the event that multiple signatures are applied to a message, all of the signature algorithms are going to be required to consume the same number of bytes of message content. This means that the mixing of the different schemes in a single message is not supported, and if a recovery signature scheme is used, then the same amount of content needs to be consumed by all of the signatures. + The second scheme is signature with message recovery (an example of such an algorithm is ). In this scheme, the message content is processed, but part of it is included in the signature. Moving bytes of the message content into the signature allows for smaller signatures; the signature size is still potentially large, but the message content has shrunk. This has implications for systems implementing these algorithms and for applications that use them. The first is that the message content is not fully available until after a signature has been validated. Until that point, the part of the message contained inside of the signature is unrecoverable. The second is that the security analysis of the strength of the signature is very much based on the structure of the message content. Messages that are highly predictable require additional randomness to be supplied as part of the signature process. In the worst case, it becomes the same as doing a signature with appendix. Finally, in the event that multiple signatures are applied to a message, all of the signature algorithms are going to be required to consume the same number of bytes of message content. This means that the mixing of the different schemes in a single message is not supported, and if a recovery signature scheme is used, then the same amount of content needs to be consumed by all of the signatures. The signature functions for this scheme are: -
- - signature, message sent = Sign(message content, key) +
+ +signature, message sent = Sign(message content, key) - valid, message content = Verification(message sent, key, signature) +valid, message content = Verification(message sent, key, signature)
Signature algorithms are used with the COSE_Signature and COSE_Sign1 structures. At this time, only signatures with appendixes are defined for use with COSE; however, considerable interest has been expressed in using a signature with message recovery algorithm due to the effective size reduction that is possible. Implementations will need to keep this in mind for later possible integration.
-
- Message Authentication Codes (MACs) provide data authentication and integrity protection. They provide either no or very limited data origination. A MAC, for example, can be used to prove the identity of the sender to a third party. +
+ Message Authentication Codes (MACs) provide data authentication and integrity protection. They provide either no or very limited data origination. A MAC, for example, cannot be used to prove the identity of the sender to a third party. MACs use the same scheme as signature with appendix algorithms. The message content is processed and an authentication code is produced. The authentication code is frequently called a tag. The MAC functions are: -
- +
+ tag = MAC_Create(message content, key) valid = MAC_Verify(message content, key, tag) @@ -867,15 +1064,15 @@ valid = MAC_Verify(message content, key, tag) MAC algorithms are used in the COSE_Mac and COSE_Mac0 structures.
-
+
Content encryption algorithms provide data confidentiality for potentially large blocks of data using a symmetric key. They provide integrity on the data that was encrypted; however, they provide either no or very limited data origination. (One cannot, for example, be used to prove the identity of the sender to a third party.) The ability to provide data origination is linked to how the CEK is obtained. COSE restricts the set of legal content encryption algorithms to those that support authentication both of the content and additional data. The encryption process will generate some type of authentication value, but that value may be either explicit or implicit in terms of the algorithm definition. For simplicity's sake, the authentication code will normally be defined as being appended to the ciphertext stream. The encryption functions are: -
- +
+ ciphertext = Encrypt(message content, key, additional data) -valid, message content = Decrypt(cipher text, key, additional data) +valid, message content = Decrypt(ciphertext, key, additional data)
Most AEAD algorithms are logically defined as returning the message content only if the decryption is valid. Many but not all implementations will follow this convention. The message content MUST NOT be used if the decryption does not validate. @@ -883,22 +1080,36 @@ valid, message content = Decrypt(cipher text, key, additional data)
-
+
KDFs are used to take some secret value and generate a different one. The secret value comes in three flavors: Secrets that are uniformly random: This is the type of secret that is created by a good random number generator.Secrets that are not uniformly random: This is type of secret that is created by operations like key agreement. Secrets that are not random: This is the type of secret that people generate for things like passwords. - General KDFs work well with the first type of secret, can do reasonably well with the second type of secret, and generally do poorly with the last type of secret. None of the KDFs in this section are designed to deal with the type of secrets that are used for passwords. Functions like PBES2 need to be used for that type of secret. + + General KDFs work well with the first type of secret, can do reasonably well with the second type of secret, and generally do poorly with the last type of secret. + + Functions like PBES2 need to be used for non-random secrets. + - The same KDF can be set up to deal with the first two types of secrets in a different way. The KDF defined in !!! HDKF !!! is such a function. This is reflected in the set of algorithms defined for the HMAC-based Extract-and-Expand Key Derivation Function (HKDF). + + The same KDF can be set up to deal with the first two types of secrets in a different way. + The KDF defined in !!! HDKF !!! (section XXXX of ) is such a function. + This is reflected in the set of algorithms defined around the HMAC-based Extract-and-Expand Key Derivation Function (HKDF). + When using KDFs, one component that is included is context information. Context information is used to allow for different keying information to be derived from the same secret. The use of context-based keying material is considered to be a good security practice.
-
- Content key distribution methods (recipient algorithms) can be defined into a number of different classes. COSE has the ability to support many classes of recipient algorithms. In this section, a number of classes are listed, and then a set of algorithms are specified for each of the classes. The names of the recipient algorithm classes used here are the same as those defined in . Other specifications use different terms for the recipient algorithm classes or do not support some of the recipient algorithm classes. +
+ + Content key distribution methods (recipient algorithms) can be defined into a number of different classes. + COSE has the ability to support many classes of recipient algorithms. + In this section, a number of classes are listed. + The names of the recipient algorithm classes used here are the same as those defined in . + Other specifications use different terms for the recipient algorithm classes or do not support some of the recipient algorithm classes. + -
+
The direct encryption class algorithms share a secret between the sender and the recipient that is used either directly or after manipulation as the CEK. When direct encryption mode is used, it MUST be the only mode used on the message. The COSE_Recipient structure for the recipient is organized as follows: @@ -910,18 +1121,27 @@ valid, message content = Decrypt(cipher text, key, additional data) The 'ciphertext' field MUST be a zero-length item. The 'recipients' field MUST be absent.
-
+
In key wrap mode, the CEK is randomly generated and that key is then encrypted by a shared secret between the sender and the recipient. All of the currently defined key wrap algorithms for COSE are AE algorithms. Key wrap mode is considered to be superior to direct encryption if the system has any capability for doing random key generation. This is because the shared key is used to wrap random data rather than data that has some degree of organization and may in fact be repeating the same content. The use of key wrap loses the weak data origination that is provided by the direct encryption algorithms. The COSE_Encrypt structure for the recipient is organized as follows: - -The 'protected' field MUST be absent if the key wrap algorithm is an AE algorithm. + + + The 'protected' field MUST be absent if the key wrap algorithm is an AE algorithm. -The 'recipients' field is normally absent, but can be used. Applications MUST deal with a recipient field being present, not being able to decrypt that recipient is an acceptable way of dealing with it. Failing to process the message is not an acceptable way of dealing with it. The plaintext to be encrypted is the key from next layer down (usually the content layer). -At a minimum, the 'unprotected' field MUST contain the 'alg' parameter and SHOULD contain a parameter identifying the shared secret. + + The 'recipients' field is normally absent, but can be used. + Applications MUST deal with a recipient field being present that has an unsupported algorthms, not being able to decrypt that recipient is an acceptable way of dealing with it. + Failing to process the message is not an acceptable way of dealing with it. + + The plaintext to be encrypted is the key from next layer down (usually the content layer). + + At a minimum, the 'unprotected' field MUST contain the 'alg' parameter and SHOULD contain a parameter identifying the shared secret. + +
-
+
Key transport mode is also called key encryption mode in some standards. Key transport mode differs from key wrap mode in that it uses an asymmetric encryption algorithm rather than a symmetric encryption algorithm to protect the key. This document does not define any key transport mode algorithms. When using a key transport algorithm, the COSE_Encrypt structure for the recipient is organized as follows: @@ -930,13 +1150,19 @@ valid, message content = Decrypt(cipher text, key, additional data) At a minimum, the 'unprotected' field MUST contain the 'alg' parameter and SHOULD contain a parameter identifying the asymmetric key.
-
- The 'direct key agreement' class of recipient algorithms uses a key agreement method to create a shared secret. A KDF is then applied to the shared secret to derive a key to be used in protecting the data. This key is normally used as a CEK or MAC key, but could be used for other purposes if more than two layers are in use (see ). - The most commonly used key agreement algorithm is Diffie-Hellman, but other variants exist. Since COSE is designed for a store and forward environment rather than an online environment, many of the DH variants cannot be used as the receiver of the message cannot provide any dynamic key material. One side effect of this is that perfect forward secrecy (see ) is not achievable. A static key will always be used for the receiver of the COSE object. - Two variants of DH that are supported are: -Ephemeral-Static (ES) DH: where the sender of the message creates a one-time DH key and uses a static key for the recipient. The use of the ephemeral sender key means that no additional random input is needed as this is randomly generated for each message. +
+ The 'direct key agreement' class of recipient algorithms uses a key agreement method to create a shared secret. A KDF is then applied to the shared secret to derive a key to be used in protecting the data. This key is normally used as a CEK or MAC key, but could be used for other purposes if more than two layers are in use (see ). + The most commonly used key agreement algorithm is Diffie-Hellman, but other variants exist. Since COSE is designed for a store and forward environment rather than an online environment, many of the DH variants cannot be used as the receiver of the message cannot provide any dynamic key material. One side effect of this is that perfect forward secrecy (see ) is not achievable. A static key will always be used for the receiver of the COSE object. + + Two variants of DH that are supported are: + + Ephemeral-Static (ES) DH: where the sender of the message creates a one-time DH key and uses a static key for the recipient. The use of the ephemeral sender key means that no additional random input is needed as this is randomly generated for each message. -Static-Static DH: where a static key is used for both the sender and the recipient. The use of static keys allows for the recipient to get a weak version of data origination for the message. When static-static key agreement is used, then some piece of unique data for the KDF is required to ensure that a different key is created for each message. + + Static-Static (SS) DH: where a static key is used for both the sender and the recipient. The use of static keys allows for the recipient to get a weak version of data origination for the message. When static-static key agreement is used, then some piece of unique data for the KDF is required to ensure that a different key is created for each message. + + + When direct key agreement mode is used, there MUST be only one recipient in the message. This method creates the key directly, and that makes it difficult to mix with additional recipients. If multiple recipients are needed, then the version with key wrap needs to be used. @@ -944,10 +1170,10 @@ valid, message content = Decrypt(cipher text, key, additional data) At a minimum, headers MUST contain the 'alg' parameter and SHOULD contain a parameter identifying the recipient's asymmetric key. The headers SHOULD identify the sender's key for the static-static versions and MUST contain the sender's ephemeral key for the ephemeral-static versions.
-
+
Key Agreement with Key Wrap uses a randomly generated CEK. The CEK is then encrypted using a key wrap algorithm and a key derived from the shared secret computed by the key agreement algorithm. The function for this would be: -
- +
+ encryptedKey = KeyWrap(KDF(DH-Shared, context), CEK)
@@ -969,15 +1195,22 @@ encryptedKey = KeyWrap(KDF(DH-Shared, context), CEK) Applications MUST NOT generate messages with the same label used twice as a key in a single map. Applications MUST NOT parse and process messages with the same label used twice as a key in a single map. Applications can enforce the parse and process requirement by using parsers that will fail the parse step or by using parsers that will pass all keys to the application, and the application can perform the check for duplicate keys.
- This document is designed to provide a set of security services, but not implementation requirements for specific usage. The interoperability requirements are provided for how each of the individual services are used and how the algorithms are to be used for interoperability. The requirements about which algorithms and which services are needed are deferred to each application. + This document is designed to provide a set of security services, but not impose algorithm implementation requirements for specific usage. The interoperability requirements are provided for how each of the individual services are used and how the algorithms are to be used for interoperability. The requirements about which algorithms and which services are needed are deferred to each application. - An example of a profile can be found in where two profiles are being developed. One is for carrying content by itself, and the other is for carrying content in combination with CoAP headers. + + An example of a profile can be found in where a profiles was developed for carrying content in combination with CoAP headers. + It is intended that a profile of this document be created that defines the interoperability requirements for that specific application. This section provides a set of guidelines and topics that need to be considered when profiling this document. Applications need to determine the set of messages defined in this document that they will be using. The set of messages corresponds fairly directly to the set of security services that are needed and to the security levels needed. -Applications may define new header parameters for a specific purpose. Applications will often times select specific header parameters to use or not to use. For example, an application would normally state a preference for using either the IV or the Partial IV parameter. If the Partial IV parameter is specified, then the application would also need to define how the fixed portion of the IV would be determined. + + Applications may define new header parameters for a specific purpose. + Applications will often times select specific header parameters to use or not to use. + For example, an application would normally state a preference for using either the IV or the Partial IV parameter. + If the Partial IV parameter is specified, then the application also needs to define how the fixed portion of the IV is determined. + -When applications use externally defined authenticated data, they need to define how that data is encoded. This document assumes that the data will be provided as a byte stream. More information can be found in . +When applications use externally defined authenticated data, they need to define how that data is encoded. This document assumes that the data will be provided as a byte string. More information can be found in . Applications need to determine the set of security algorithms that are to be used. When selecting the algorithms to be used as the mandatory-to-implement set, consideration should be given to choosing different types of algorithms when two are chosen for a specific purpose. An example of this would be choosing HMAC-SHA512 and AES-CMAC as different MAC algorithms; the construction is vastly different between these two algorithms. This means that a weakening of one algorithm would be unlikely to lead to a weakening of the other algorithms. Of course, these algorithms do not provide the same level of security and thus may not be comparable for the desired security functionality. @@ -993,338 +1226,52 @@ encryptedKey = KeyWrap(KDF(DH-Shared, context), CEK) The registeries and registrations listed below were created during processing of RFC 8152 . The only known action at this time is to update the references. - +
- IANA has assigned the following tags from the "CBOR Tags" registry. The tags for COSE_Sign1, COSE_Encrypt0, and COSE_Mac0 were assigned in the 1 to 23 value range (one byte long when encoded). The tags for COSE_Sign, COSE_Encrypt, and COSE_Mac were assigned in the 24 to 255 value range (two bytes long when encoded). - The tags assigned are in . + + IANA assigned tags in the "CBOR Tags" registry as part of processing . + IANA is requested to update the references from to this document. +
- IANA has created a registry titled "COSE Header Parameters". - The registry has been created to use the "Expert Review Required" registration procedure . - Guidelines for the experts are provided in . - It should be noted that, in addition to the expert review, some portions of the registry require a specification, potentially a Standards Track RFC, be supplied as well. - - - The columns of the registry are: - - - The name is present to make it easier to refer to and discuss the registration entry. - The value is not used in the protocol. - Names are to be unique in the table. - - - -This is the value used for the label. - The label can be either an integer or a string. - Registration in the table is based on the value of the label requested. - Integer values between 1 and 255 and strings of length 1 are designated as "Standards Action". -Integer values from 256 to 65535 and strings of length 2 are designated as "Specification Required". -Integer values of greater than 65535 and strings of length greater than 2 are designated as "Expert Review". -Integer values in the range -1 to -65536 are "delegated to the COSE Header Algorithm Parameters registry". -Integer values less than -65536 are marked as private use. - - - - This contains the CBOR type for the value portion of the label. - - - -This contains a pointer to the registry used to contain values where the set is limited. - - - This contains a brief description of the header field. - - - This contains a pointer to the specification defining the header field (where public). - - + IANA created a registry titled "COSE Header Parameters" as part of processing . + The registry has been created to use the "Expert Review Required" registration procedure . - The initial contents of the registry is ... - + IANA is requested to update the reference for entries in the table from to this document. + This document does not update the expert review guidelines provided in .
+
- IANA has created a registry titled "COSE Header Algorithm Parameters". - The registry uses the "Expert Review Required" registration procedure. - Expert review guidelines are provided in . - - - - The columns of the registry are: - - - -The name is present to make it easier to refer to and discuss the registration entry. - The value is not used in the protocol. - - - -The algorithm(s) that this registry entry is used for. - This value is taken from the "COSE Algorithms" registry. - Multiple algorithms can be specified in this entry. - For the table, the algorithm/label pair MUST be unique. - - - -This is the value used for the label. - The label is an integer in the range of -1 to -65536. - - - -This contains the CBOR type for the value portion of the label. - - - - This contains a brief description of the header field. - - - -This contains a pointer to the specification defining the header field (where public). - - - - - -
- -
- - IANA has created a registry titled "COSE Algorithms". - The registry has been created to use the "Expert Review Required" registration procedure. - Guidelines for the experts are provided in . - It should be noted that, in addition to the expert review, some portions of the registry require a specification, potentially a Standards Track RFC, be supplied as well. - - - - - - - - - - A value that can be used to identify an algorithm in documents for easier comprehension. - The name SHOULD be unique. -However, the 'Value' field is what is used to identify the algorithm, not the 'name' field. - - -The value to be used to identify this algorithm. - Algorithm values MUST be unique. - The value can be a positive integer, a negative integer, or a string. - Integer values between -256 and 255 and strings of length 1 are designated as "Standards Action". - Integer values from -65536 to 65535 and strings of length 2 are designated as "Specification Required". - Integer values greater than 65535 and strings of length greater than 2 are designated as "Expert Review". - Integer values less than -65536 are marked as private use. - - - - A short description of the algorithm. - - - A document where the algorithm is defined (if publicly available). - - - Does the IETF have a consensus recommendation to use the algorithm? The legal values are 'Yes', 'No', and 'Deprecated'. - - - - - - - NOTE: The assignment of algorithm identifiers in this document was done so that positive numbers were used for the first layer objects (COSE_Sign, COSE_Sign1, COSE_Encrypt, COSE_Encrypt0, COSE_Mac, and COSE_Mac0). - Negative numbers were used for second layer objects (COSE_Signature and COSE_recipient). - Expert reviewers should consider this practice, but are not expected to be restricted by this precedent. - -
- -
- - IANA has created a registry titled "COSE Key Common Parameters". - The registry has been created to use the "Expert Review Required" registration procedure. - Guidelines for the experts are provided in . - It should be noted that, in addition to the expert review, some portions of the registry require a specification, potentially a Standards Track RFC, be supplied as well. - - - - The columns of the registry are: - - - - -This is a descriptive name that enables easier reference to the item. - It is not used in the encoding. - - -The value to be used to identify this algorithm. - Key map labels MUST be unique. - The label can be a positive integer, a negative integer, or a string. - Integer values between 0 and 255 and strings of length 1 are designated as "Standards Action". - Integer values from 256 to 65535 and strings of length 2 are designated as "Specification Required". - Integer values of greater than 65535 and strings of length greater than 2 are designated as "Expert Review". - Integer values in the range -65536 to -1 are "used for key parameters specific to a single algorithm delegated to the COSE Key Type Parameters registry". - Integer values less than -65536 are marked as private use. - - - -This field contains the CBOR type for the field. - - - This field denotes the registry that values come from, if one exists. - - - This field contains a brief description for the field. - - - This contains a pointer to the public specification for the field if one exists. - - + IANA created a registry titled "COSE Header Algorithm Parameters" as part of processing . + The registry has been created to use the "Expert Review Required" registration procedure . - -
- -
- - IANA has created a registry titled "COSE Key Type Parameters". - The registry has been created to use the "Expert Review Required" registration procedure. - Expert review guidelines are provided in . - - - - The columns of the table are: - - - - - - This field contains a descriptive string of a key type. - This should be a value that is in the "COSE Key Common Parameters" registry and is placed in the 'kty' field of a COSE Key structure. - - - - This is a descriptive name that enables easier reference to the item. - It is not used in the encoding. - - - - The label is to be unique for every value of key type. - The range of values is from -65536 to -1. - Labels are expected to be reused for different keys. - - - - This field contains the CBOR type for the field. - - - -This field contains a brief description for the field. - - - - This contains a pointer to the public specification for the field if one exists. - - - - - +
-
- - IANA has created a new registry titled "COSE Key Types". - The registry has been created to use the "Expert Review Required" registration procedure. - Expert review guidelines are provided in . - +
- The columns of this table are: - - - This is a descriptive name that enables easier reference to the item. - The name MUST be unique. - It is not used in the encoding. - - - This is the value used to identify the curve. - These values MUST be unique. - The value can be a positive integer, a negative integer, or a string. - - - This field contains a brief description of the curve. - - - This contains a pointer to the public specification for the curve if one exists. - - - - -
- -
- - IANA has created a registry titled "COSE Elliptic Curves". - The registry has been created to use the "Expert Review Required" registration procedure. - Guidelines for the experts are provided in . - It should be noted that, in addition to the expert review, some portions of the registry require a specification, potentially a Standards Track RFC, be supplied as well. - - - The columns of the table are: + IANA created a registry titled "COSE Key Common Parameters" as part of the processing of . + The registry has been created to use the "Expert Review Required" registration procedure . - - - This is a descriptive name that enables easier reference to the item. - It is not used in the encoding. - - - This is the value used to identify the curve. - These values MUST be unique. - The integer values from -256 to 255 are designated as "Standards Action". - The integer values from 256 to 65535 and -65536 to -257 are designated as "Specification Required". - Integer values over 65535 are designated as "Expert Review". - Integer values less than -65536 are marked as private use. - - - - This designates the key type(s) that can be used with this curve. - - - This field contains a brief description of the curve. - - - This contains a pointer to the public specification for the curve if one exists. - - - Does the IETF have a consensus recommendation to use the algorithm? The legal values are 'Yes', 'No', and 'Deprecated'. - - + IANA is requested to update the reference for entries in the table from to this document. + This document does not update the expert review guidelines provided in . -
+
@@ -1333,7 +1280,7 @@ This field contains a brief description for the field. Type name: applicationSubtype name: cose Required parameters: N/A Optional parameters: cose-typeEncoding considerations: binary -Security considerations: See the Security Considerations section of RFC 8152. +Security considerations: See the Security Considerations section of [[This Document]]. Interoperability considerations: N/A Published specification: RFC 8152 Applications that use this media type: IoT applications sending security content over HTTP(S) transports. @@ -1357,7 +1304,7 @@ This field contains a brief description for the field. Type name: applicationSubtype name: cose-keyRequired parameters: N/A Optional parameters: N/A Encoding considerations: binary -Security considerations: See the Security Considerations section of RFC 8152. +Security considerations: See the Security Considerations section of [[This Document]]. Interoperability considerations: N/A Published specification: RFC 8152 Applications that use this media type: Distribution of COSE based keys for IoT applications. @@ -1378,7 +1325,7 @@ This field contains a brief description for the field. Required parameters: N/A Optional parameters: N/A Encoding considerations: binary -Security considerations: See the Security Considerations section of RFC 8152. +Security considerations: See the Security Considerations section of [[This Document]]. Interoperability considerations: N/A Published specification: RFC 8152 Applications that use this media type: Distribution of COSE based keys for IoT applications. @@ -1398,45 +1345,11 @@ This field contains a brief description for the field.
- IANA has added the following entries to the "CoAP Content-Formats" registry. - - Media Type - Encoding - ID - Reference - application/cose; cose-type="cose-sign" - - 98 - [RFC8152] - application/cose; cose-type="cose-sign1" - - 18 - [RFC8152] - application/cose; cose-type="cose-encrypt" - - 96 - [RFC8152] - application/cose; cose-type="cose-encrypt0" - - 16 - [RFC8152] - application/cose; cose-type="cose-mac" - - 97 - [RFC8152] - application/cose; cose-type="cose-mac0" - - 17 - [RFC8152] - application/cose-key - - 101 - [RFC8152] - application/cose-key-set - - 102 - [RFC8152] - + + IANA added the following entries to the "CoAP Content-Formats" registry while processing . + IANA is requested to update the reference value from to [[This Document]]. + +
All of the IANA registries established in this document are defined as expert review. This section gives some general guidelines for what the experts should be looking for, but they are being designated as experts for a reason, so they should be given substantial latitude. @@ -1482,32 +1395,36 @@ This field contains a brief description for the field. - -Constrained RESTful Environments (CoRE) Parameters + +CoAP Content-Formats +IANA + + + + +COSE Algorithms +IANA + + + + + +COSE Key Parameters +IANA + + + + + +COSE Key Types IANA - - - - - - - - - -Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC -National Institute of Standards and Technology - - - - - Digital Signature Standard (DSS) National Institute of Standards and Technology @@ -1516,20 +1433,6 @@ This field contains a brief description for the field. - -Computer Data Authentication -National Institute of Standards and Technology - - - - - -SEC 1: Elliptic Curve Cryptography -Certicom Research - - - - Edwards-Curve Digital Signature Algorithm (EdDSA) @@ -1546,55 +1449,30 @@ This field contains a brief description for the field. - - -COSE ALGS - - - - - - + - + &RFC8152; - - -CBOR data definition language (CDDL): a notational convention to express CBOR data structures - - - - - - - -This document proposes a notational convention to express CBOR data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR. - - - + - - - - - + @@ -1603,21 +1481,9 @@ This field contains a brief description for the field. - - -Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography -U.S. National Institute of Standards and Technology -U.S. National Institute of Standards and Technology -U.S. National Institute of Standards and Technology -Orion Security Solutions, Inc. - - - - - Formal Security Proofs for a Signature Scheme with Partial Message Recovery @@ -1636,25 +1502,8 @@ This field contains a brief description for the field. - - -Object Security of CoAP (OSCOAP) - - - - - - - - - - - - - - - - + +
@@ -1664,7 +1513,7 @@ This field contains a brief description for the field.
In this section, three sets of recommendations are laid out. The first set of recommendations apply to having an implicit algorithm identified for a single layer of a COSE object. The second set of recommendations apply to having multiple implicit algorithms identified for multiple layers of a COSE object. The third set of recommendations apply to having implicit algorithms for multiple COSE object constructs. - The key words from RFC 2119 are deliberately not used here. This specification can provide recommendations, but it cannot enforce them. + The key words from are deliberately not used here. This specification can provide recommendations, but it cannot enforce them. This set of recommendations applies to the case where an application is distributing a fixed algorithm along with the key information for use in a single COSE object. This normally applies to the smallest of the COSE objects, specifically COSE_Sign1, COSE_Mac0, and COSE_Encrypt0, but could apply to the other structures as well. The following items should be taken into account: @@ -1697,7 +1546,7 @@ This field contains a brief description for the field. There is a group of people who want to have a counter signature parameter that is directly tied to the value being signed, and thus the authenticated and unauthenticated buckets can be removed from the message being sent. The focus on this is an even smaller size, as all of the information on the process of creating the counter signature is implicit rather than being explicitly carried in the message. This includes not only the algorithm identifier as presented above, but also items such as the key identification, which is always external to the signature structure. This means that the entities that are doing the validation of the counter signature are required to infer which key is to be used from context rather than being explicit. One way of doing this would be to presume that all data coming from a specific port (or to a specific URL) is to be validated by a specific key. (Note that this does not require that the key identifier be part of the value signed as it does not serve a cryptographic purpose. If the key validates the counter signature, then it should be presumed that the entity associated with that key produced the signature.) When computing the signature for the bare counter signature header, the same Sig_structure defined in is used. The sign_protected field is omitted, as there is no protected header field in this counter signature header. The value of "CounterSignature0" is placed in the context field of the Sig_stucture. - + Name Label Value Type @@ -1724,8 +1573,8 @@ This field contains a brief description for the field. Layer 2: Uses ECDH Ephemeral-Static direct to generate the layer 1 key. In effect, this example is a decomposed version of using the ECDH&nbhy;ES+A128KW algorithm. Size of binary file is 183 bytes -
- +
+ 96( [ / protected / h'a10101' / { @@ -1769,23 +1618,23 @@ e9b8a55a600b21233e86e68',
- This appendix includes a set of examples that show the different features and message types that have been defined in this document. To make the examples easier to read, they are presented using the extended CBOR diagnostic notation (defined in ) rather than as a binary dump. + This appendix includes a set of examples that show the different features and message types that have been defined in this document. To make the examples easier to read, they are presented using the extended CBOR diagnostic notation (defined in ) rather than as a binary dump. A GitHub project has been created at <https://github.com/cose-wg/Examples> that contains not only the examples presented in this document, but a more complete set of testing examples as well. Each example is found in a JSON file that contains the inputs used to create the example, some of the intermediate values that can be used in debugging the example and the output of the example presented in both a hex and a CBOR diagnostic notation format. Some of the examples at the site are designed failure testing cases; these are clearly marked as such in the JSON file. If errors in the examples in this document are found, the examples on GitHub will be updated, and a note to that effect will be placed in the JSON file. As noted, the examples are presented using the CBOR's diagnostic notation. A Ruby-based tool exists that can convert between the diagnostic notation and binary. This tool can be installed with the command line: -
- gem install cbor-diag +
+ gem install cbor-diag
The diagnostic notation can be converted into binary files using the following command line: -
- diag2cbor.rb < inputfile > outputfile +
+ diag2cbor.rb < inputfile > outputfile
The examples can be extracted from the XML version of this document via an XPath expression as all of the artwork is tagged with the attribute type='CBORdiag'. (Depending on the XPath evaluator one is using, it may be necessary to deal with &gt; as an entity.) -
- //artwork[@type='CDDL']/text() +
+ //artwork[@type='CDDL']/text()
@@ -1795,8 +1644,8 @@ e9b8a55a600b21233e86e68', Signature Algorithm: ECDSA w/ SHA-256, Curve P-256 Size of binary file is 103 bytes -
- +
+ 98( [ / protected / h'', @@ -1830,8 +1679,8 @@ e9b8a55a600b21233e86e68', Size of binary file is 277 bytes -
- +
+ 98( [ / protected / h'', @@ -1877,8 +1726,8 @@ c5b07ec6d722e3835adb5b2d8c44e95ffb13877dd2582866883535de3bb03d01753f Size of binary file is 180 bytes -
- +
+ 98( [ / protected / h'', @@ -1920,8 +1769,8 @@ c5b07ec6d722e3835adb5b2d8c44e95ffb13877dd2582866883535de3bb03d01753f Size of binary file is 125 bytes -
- +
+ 98( [ / protected / h'a2687265736572766564f40281687265736572766564' / @@ -1960,8 +1809,8 @@ c5b07ec6d722e3835adb5b2d8c44e95ffb13877dd2582866883535de3bb03d01753f Size of binary file is 98 bytes -
- +
+ 18( [ / protected / h'a10126' / { @@ -1986,8 +1835,8 @@ a4c345cacb36' Size of binary file is 151 bytes -
- +
+ 96( [ / protected / h'a10101' / { @@ -2036,8 +1885,8 @@ bf054e1c7b4d91d6280', Supplementary Public Other: "Encryption Example 02" Size of binary file is 91 bytes -
- +
+ 96( [ / protected / h'a1010a' / { @@ -2073,8 +1922,8 @@ bf054e1c7b4d91d6280', Size of binary file is 326 bytes -
- +
+ 96( [ / protected / h'a10101' / { @@ -2130,8 +1979,8 @@ bf054e1c7b4d91d6280', Size of binary file is 173 bytes -
- +
+ 96( [ / protected / h'a10101' / { @@ -2169,8 +2018,8 @@ e1c62' Size of binary file is 52 bytes -
- +
+ 16( [ / protected / h'a1010a' / { @@ -2190,8 +2039,8 @@ e1c62' This example uses the following: CEK: AES-CCM w/ 128-bit key and a 64-bit tagPrefix for IV is 89F52F65A1C580933B52 Size of binary file is 41 bytes -
- +
+ 16( [ / protected / h'a1010a' / { @@ -2220,8 +2069,8 @@ RFC Editor - All of the examples will need to be modified after IANA has finaize Size of binary file is 57 bytes -
- +
+ 97( [ / protected / h'a1010f' / { @@ -2251,8 +2100,8 @@ RFC Editor - All of the examples will need to be modified after IANA has finaize Recipient class: ECDH key agreement, two static keys, HKDF w/ context structure Size of binary file is 214 bytes -
- +
+ 97( [ / protected / h'a10105' / { @@ -2288,8 +2137,8 @@ RFC Editor - All of the examples will need to be modified after IANA has finaize Recipient class: AES Key Wrap w/ a pre-shared 256-bit key Size of binary file is 109 bytes -
- +
+ 97( [ / protected / h'a1010e' / { @@ -2326,8 +2175,8 @@ b6eb0' AES Key Wrap w/ 256-bit key Size of binary file is 309 bytes -
- +
+ 97( [ / protected / h'a10105' / { @@ -2379,9 +2228,9 @@ a69e8c07dfbca5bb1f661bc5f8e0df9e3eff5' Recipient class: direct shared secret Size of binary file is 37 bytes -
+
- + 17( [ / protected / h'a1010f' / { @@ -2404,9 +2253,9 @@ a69e8c07dfbca5bb1f661bc5f8e0df9e3eff5' Size of binary file is 481 bytes -
+
- + [ { -1:1, @@ -2458,8 +2307,8 @@ d6280', An EC key with a kid of "bilbo.baggins@hobbiton.example"An EC key with a kid of "11" Size of binary file is 816 bytes -
- +
+ [ { 1:2,