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Reword description of the authentation tag computation stages

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Signed-off-by: Mateusz Starzyk <mateusz.starzyk@mobica.com>
This commit is contained in:
Mateusz Starzyk 2021-06-15 14:26:53 +02:00
parent 25a571e076
commit 3d0bbeef0c
1 changed files with 15 additions and 8 deletions
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23
library/gcm.c
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@ -333,14 +333,21 @@ int mbedtls_gcm_starts( mbedtls_gcm_context *ctx,
}
/**
* mbedtls_gcm_context::buf contains different data type, depending
* on the values of mbedtls_gcm_context::::add_len and
* mbedtls_gcm_context::len:
* * When add_len % 16 == 0 and len == 0: initial state.
* * When add_len % 16 != 0 and len == 0: the first `add_len % 16` bytes
* of buf have a partial AD block xored in and not yet multiplied in.
* * When len != 0: the first `add_len % 16` bytes of buf have partial
* ciphertext xored in and not yet multiplied in.
* mbedtls_gcm_context::buf contains the partial state of the computation of
* the authentication tag.
* mbedtls_gcm_context::::add_len and mbedtls_gcm_context::len indicate
* differenet stages of the computation:
* * len == 0 && add_len == 0: initial state
* * len == 0 && add_len % 16 != 0: the first `add_len % 16` bytes have
* a partial block of AD that has been
* xored in but not yet multiplied in.
* * len == 0 && add_len % 16 == 0: the authentication tag is correct if
* the data ends now.
* * len % 16 != 0: the first `len % 16` bytes have
* a partial block of ciphertext that has
* been xored in but not yet multiplied in.
* * len > 0 && len % 16 == 0: the authentication tag is correct if
* the data ends now.
*/
int mbedtls_gcm_update_ad( mbedtls_gcm_context *ctx,
const unsigned char *add, size_t add_len )