[FAB-830] CC encryption doc

This commit simply offers some high level explanation
on the merits of cc encryption.
Incorporate Dave E feedback;
Add content on the extension interface and helper
program to the chaincode4ade doc.
Incorporate Ale feedback
[ci-skip]

Change-Id: I5792fdfd4c8db0a84efffb4cea8288b11cd410d6
Signed-off-by: Nick Gaski <ngaski@us.ibm.com>

docs/source/chaincode4ade.rst

@@ -523,5 +523,28 @@ By default, we mount only ``sacc``.  However, you can easily test different
 chaincodes by adding them to the ``chaincode`` subdirectory and relaunching
 your network.  At this point they will be accessible in your ``chaincode`` container.
 
+Chaincode encryption
+--------------------
+
+In certain scenarios, it may be useful to encrypt values associated with a key
+in their entirety or simply in part.  For example, if a person's social security
+number or address was being written to the ledger, then you likely would not want
+this data to appear in plaintext.  Chaincode encryption is achieved by leveraging
+the `entities extension <https://github.com/hyperledger/fabric/tree/master/core/chaincode/shim/ext/entities>`__
+which is a BCCSP wrapper with commodity factories and functions to perform cryptographic
+operations such as encryption and elliptic curve digital signatures.  For example,
+to encrypt, the invoker of a chaincode passes in a cryptographic key via the
+transient field.  The same key may then be used for subsequent query operations, allowing
+for proper decryption of the encrypted state values.
+
+For more information and samples, see the
+`Encc Example <https://github.com/hyperledger/fabric/tree/master/examples/chaincode/go/enccc_example>`__
+within the ``fabric/examples`` directory.  Pay specific attention to the ``utils.go``
+helper program.  This utility loads the chaincode shim APIs and Entities extension
+and builds a new class of functions (e.g. ``encryptAndPutState`` & ``getStateAndDecrypt``)
+that the sample encryption chaincode then leverages.  As such, the chaincode can
+now marry the basic shim APIs of ``Get`` and ``Put`` with the added functionality of
+``Encrypt`` and ``Decrypt``.
+
 .. Licensed under Creative Commons Attribution 4.0 International License
    https://creativecommons.org/licenses/by/4.0/

docs/source/fabric_model.rst

@@ -94,9 +94,14 @@ thereby isolate/segregate their transactions and ledger.  In order to solve
 scenarios that want to bridge the gap between total transparency and privacy,
 chaincode can be installed only on peers that need to access the asset states
 to perform reads and writes (in other words, if a chaincode is not installed on
-a peer, it will not be able to properly interface with the ledger).  To further
-obfuscate the data, values within chaincode can be encrypted (in part or in total) using common
-cryptographic algorithms such as AES before appending to the ledger.
+a peer, it will not be able to properly interface with the ledger).
+
+To further obfuscate the data, values within chaincode can be encrypted
+(in part or in total) using common cryptographic algorithms such as AES before
+sending transactions to the ordering service and appending blocks to the ledger.
+Once encrypted data has been written to the ledger, it can only be decrypted by
+a user in possession of the corresponding key that was used to generate the cipher text.  
+For further details on chaincode encryption, see the :doc:`chaincode4ade` topic.
 
 .. _Security-Membership-Services: