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Clarify documentation for AES OFB

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1. Changed reference/link to NIST SP800-38A
 2. Clarified language around AES-OFB usage
This commit is contained in:
Simon Butcher 2018-06-04 22:11:25 +01:00
parent 33cb519cda
commit 5db13621ec
2 changed files with 24 additions and 23 deletions
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45
include/mbedtls/aes.h
View File

@ -298,34 +298,35 @@ int mbedtls_aes_crypt_cfb8( mbedtls_aes_context *ctx,
#if defined(MBEDTLS_CIPHER_MODE_OFB)
/**
* \brief This function performs an AES-OFB (Output Feedback Mode) encryption
* or decryption operation.
* \brief This function performs an AES-OFB (Output Feedback Mode)
* encryption or decryption operation.
*
* For OFB, you must set up the context with mbedtls_aes_setkey_enc(),
* regardless of whether you are performing an encryption or decryption
* operation. This is because OFB mode uses the same key schedule for
* encryption and decryption.
* For OFB, you must set up the context with
* mbedtls_aes_setkey_enc(), regardless of whether you are
* performing an encryption or decryption operation. This is
* because OFB mode uses the same key schedule for encryption and
* decryption.
*
* The OFB operation is identical for encryption or decryption, therefore
* no operation mode needs to be specified.
* The OFB operation is identical for encryption or decryption,
* therefore no operation mode needs to be specified.
*
* \note Upon exit, the content of iv, the Initialisation Vector, is updated
* so that you can call the same function again on the next block(s) of
* data and get the same result as if it was encrypted in one call. This
* allows a "streaming" usage, by initialising iv_off to 0 before the
* first call, and preserving its value between calls.
* \note Upon exit, the content of iv, the Initialisation Vector, is
* updated so that you can call the same function again on the next
* block(s) of data and get the same result as if it was encrypted
* in one call. This allows a "streaming" usage, by initialising
* iv_off to 0 before the first call, and preserving its value
* between calls.
*
* For block by block usage, (or non-streaming use), the iv should be
* initialised on each call to a unique value, and iv_off set to 0 on
* each call.
* For non-streaming use, the iv should be initialised on each call
* to a unique value, and iv_off set to 0 on each call.
*
* If you need to retain the contents of the initialisation vector, you
* must either save it manually or use the cipher module instead.
*
* For the OFB mode, the initiallisation vector must be unique and must
* be unique for every encryption operation. Reuse of an initialisation
* vector will compromise security.
* If you need to retain the contents of the initialisation vector,
* you must either save it manually or use the cipher module
* instead.
*
* \warning For the OFB mode, the initiallisation vector must be unique and
* must be unique for every encryption operation. Reuse of an
* initialisation vector will compromise security.
*
* \param ctx The AES context to use for encryption or decryption.
* \param length The length of the input data.

2
library/aes.c
View File

@ -1256,7 +1256,7 @@ static const unsigned char aes_test_cfb128_ct[3][64] =
/*
* AES-OFB test vectors from:
*
* http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
* https://csrc.nist.gov/publications/detail/sp/800-38a/final
*/
static const unsigned char aes_test_ofb_key[3][32] =
{