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Clarify comments on use of AES OFB block mode

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Simon Butcher 2018-06-02 18:27:04 +01:00
parent 00131446be
commit 968646c079
1 changed files with 16 additions and 7 deletions
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23
include/mbedtls/aes.h
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@ -309,13 +309,22 @@ int mbedtls_aes_crypt_cfb8( mbedtls_aes_context *ctx,
* The OFB operation is identical for encryption or decryption, therefore * The OFB operation is identical for encryption or decryption, therefore
* no operation mode needs to be specified. * no operation mode needs to be specified.
* *
* \note Upon exit, the content of the IV is updated so that you can * \note Upon exit, the content of iv, the Initialisation Vector, is updated
* call the same function again on the next * so that you can call the same function again on the next block(s) of
* block(s) of data and get the same result as if it was * data and get the same result as if it was encrypted in one call. This
* encrypted in one call. This allows a "streaming" usage. * allows a "streaming" usage, by initialising iv_off to 0 before the
* If you need to retain the contents of the * first call, and preserving its value between calls.
* IV, you must either save it manually or use the cipher *
* module instead. * 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.
*
* 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.
* *
* *
* \param ctx The AES context to use for encryption or decryption. * \param ctx The AES context to use for encryption or decryption.