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Iotcrypt 237 hkdf doc #1920

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Aug 30, 2018
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Iotcrypt 237 hkdf doc #1920

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d0a78e9
HKDF: Fix style issue
yanesca Aug 6, 2018
08a4aeb
HKDF: Add warning to partial functions
yanesca Aug 6, 2018
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5 changes: 5 additions & 0 deletions ChangeLog
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,11 @@ Bugfix
* Fixes an issue with MBEDTLS_CHACHAPOLY_C which would not compile if
MBEDTLS_ARC4_C and MBEDTLS_CIPHER_NULL_CIPHER weren't also defined. #1890

Changes
* Add warnings to the documentation of the HKDF module to reduce the risk
of misusing the mbedtls_hkdf_extract() and mbedtls_hkdf_expand()
functions. Fixes #1775. Reported by Brian J. Murray.

= mbed TLS 2.12.0 branch released 2018-07-25

Security
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14 changes: 12 additions & 2 deletions include/mbedtls/hkdf.h
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Expand Up @@ -73,6 +73,11 @@ int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt,
* \brief Take the input keying material \p ikm and extract from it a
* fixed-length pseudorandom key \p prk.
*
* \warning This function should only be used if the security of it has been
* studied and established in that particular context (eg. TLS 1.3
* key schedule). For standard HKDF security guarantees use
* \c mbedtls_hkdf instead.
*
* \param md A hash function; md.size denotes the length of the
* hash function output in bytes.
* \param salt An optional salt value (a non-secret random value);
Expand All @@ -97,10 +102,15 @@ int mbedtls_hkdf_extract( const mbedtls_md_info_t *md,
* \brief Expand the supplied \p prk into several additional pseudorandom
* keys, which is the output of the HKDF.
*
* \warning This function should only be used if the security of it has been
* studied and established in that particular context (eg. TLS 1.3
* key schedule). For standard HKDF security guarantees use
* \c mbedtls_hkdf instead.
*
* \param md A hash function; md.size denotes the length of the hash
* function output in bytes.
* \param prk A pseudorandom key of at least md.size bytes. \p prk is usually,
* the output from the HKDF extract step.
* \param prk A pseudorandom key of at least md.size bytes. \p prk is
* usually the output from the HKDF extract step.
* \param prk_len The length in bytes of \p prk.
* \param info An optional context and application specific information
* string. This can be a zero-length string.
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