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Update CTR doc for other 128-bit block ciphers

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Manuel Pégourié-Gonnard 2018-05-24 11:59:30 +02:00
parent f5842864d8
commit 4f24e9502e
2 changed files with 64 additions and 22 deletions
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43
include/mbedtls/aes.h
View File

@ -315,18 +315,39 @@ int mbedtls_aes_crypt_cfb8( mbedtls_aes_context *ctx,
*
* There are two common strategies for managing nonces with CTR:
*
* 1. Use a counter starting at 0 or a random value. With this
* strategy, this function will increment the counter for you, so
* you only need to preserve the \p nonce_counter buffer between
* calls. With this strategy, you must not encrypt more than
* 2**128 blocks of data.
* 2. Use a randomly-generated \p nonce_counter for each call.
* With this strategy, you need to ensure the nonce is generated
* in an unbiased way and you must not encrypt more than 2**64
* blocks of data.
* 1. You can handle everything as a single message processed over
* successive calls to this function. In that case, you want to
* set \p nonce_counter and \p nc_off to 0 for the first call, and
* then preserve the values of \p nonce_counter, \p nc_off and \p
* stream_block across calls to this function as they will be
* updated by this function.
*
* Note that for both stategies, the limit is in number of blocks
* and that an AES block is 16 bytes.
* With this strategy, you must not encrypt more than 2**128
* blocks of data with the same key.
*
* 2. You can encrypt separate messages by dividing the \p
* nonce_counter buffer in two areas: the first one used for a
* per-message nonce, handled by yourself, and the second one
* updated by this function internally.
*
* For example, you might reserve the first 12 bytes for the
* per-message nonce, and the last 4 bytes for internal use. In that
* case, before calling this function on a new message you need to
* set the first 12 bytes of \p nonce_counter to your chosen nonce
* value, the last 4 to 0, and \p nc_off to 0 (which will cause \p
* stream_block to be ignored). That way, you can encrypt at most
* 2**96 messages of up to 2**32 blocks each with the same key.
*
* The per-message nonce (or information sufficient to reconstruct
* it) needs to be communicated with the ciphertext and must be unique.
* The recommended way to ensure uniqueness is to use a message
* counter. An alternative is to generate random nonces, but this
* limits the number of messages that can be securely encrypted:
* for example, with 96-bit random nonces, you should not encrypt
* more than 2**32 messages with the same key.
*
* Note that for both stategies, sizes are measured in blocks and
* that an AES block is 16 bytes.
*
* \param ctx The AES context to use for encryption or decryption.
* \param length The length of the input data.

43
include/mbedtls/camellia.h
View File

@ -197,18 +197,39 @@ int mbedtls_camellia_crypt_cfb128( mbedtls_camellia_context *ctx,
*
* There are two common strategies for managing nonces with CTR:
*
* 1. Use a counter starting at 0 or a random value. With this
* strategy, this function will increment the counter for you, so
* you only need to preserve the \p nonce_counter buffer between
* calls. With this strategy, you must not encrypt more than
* 2**128 blocks of data.
* 2. Use a randomly-generated \p nonce_counter for each call.
* With this strategy, you need to ensure the nonce is generated
* in an unbiased way and you must not encrypt more than 2**64
* blocks of data.
* 1. You can handle everything as a single message processed over
* successive calls to this function. In that case, you want to
* set \p nonce_counter and \p nc_off to 0 for the first call, and
* then preserve the values of \p nonce_counter, \p nc_off and \p
* stream_block across calls to this function as they will be
* updated by this function.
*
* Note that for both stategies, the limit is in number of blocks
* and that a CAMELLIA block is 16 bytes.
* With this strategy, you must not encrypt more than 2**128
* blocks of data with the same key.
*
* 2. You can encrypt separate messages by dividing the \p
* nonce_counter buffer in two areas: the first one used for a
* per-message nonce, handled by yourself, and the second one
* updated by this function internally.
*
* For example, you might reserve the first 12 bytes for the
* per-message nonce, and the last 4 bytes for internal use. In that
* case, before calling this function on a new message you need to
* set the first 12 bytes of \p nonce_counter to your chosen nonce
* value, the last 4 to 0, and \p nc_off to 0 (which will cause \p
* stream_block to be ignored). That way, you can encrypt at most
* 2**96 messages of up to 2**32 blocks each with the same key.
*
* The per-message nonce (or information sufficient to reconstruct
* it) needs to be communicated with the ciphertext and must be unique.
* The recommended way to ensure uniqueness is to use a message
* counter. An alternative is to generate random nonces, but this
* limits the number of messages that can be securely encrypted:
* for example, with 96-bit random nonces, you should not encrypt
* more than 2**32 messages with the same key.
*
* Note that for both stategies, sizes are measured in blocks and
* that a CAMELLIA block is 16 bytes.
*
* \param ctx CAMELLIA context
* \param length The length of the data