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Add output parameter to mbedtls_gcm_finish

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Alternative implementations of GCM may delay the output of partial
blocks from mbedtls_gcm_update(). Add an output parameter to
mbedtls_gcm_finish() to allow such implementations to pass the final
partial block back to the caller. With the software implementation,
this final output is always empty.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2021-04-15 16:48:32 +02:00
parent 441907ec30
commit 9461e45a17
5 changed files with 37 additions and 10 deletions
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15
library/gcm.c
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@ -471,8 +471,8 @@ int mbedtls_gcm_update( mbedtls_gcm_context *ctx,
}
int mbedtls_gcm_finish( mbedtls_gcm_context *ctx,
unsigned char *tag,
size_t tag_len )
unsigned char *output, size_t output_len,
unsigned char *tag, size_t tag_len )
{
unsigned char work_buf[16];
size_t i;
@ -482,6 +482,11 @@ int mbedtls_gcm_finish( mbedtls_gcm_context *ctx,
GCM_VALIDATE_RET( ctx != NULL );
GCM_VALIDATE_RET( tag != NULL );
/* We never pass any output in finish(). The output parameter exists only
* for the sake of alternative implementations. */
(void) output;
(void) output_len;
orig_len = ctx->len * 8;
orig_add_len = ctx->add_len * 8;
@ -541,7 +546,7 @@ int mbedtls_gcm_crypt_and_tag( mbedtls_gcm_context *ctx,
if( ( ret = mbedtls_gcm_update( ctx, length, input, output ) ) != 0 )
return( ret );
if( ( ret = mbedtls_gcm_finish( ctx, tag, tag_len ) ) != 0 )
if( ( ret = mbedtls_gcm_finish( ctx, NULL, 0, tag, tag_len ) ) != 0 )
return( ret );
return( 0 );
@ -979,7 +984,7 @@ int mbedtls_gcm_self_test( int verbose )
goto exit;
}
ret = mbedtls_gcm_finish( &ctx, tag_buf, 16 );
ret = mbedtls_gcm_finish( &ctx, NULL, 0, tag_buf, 16 );
if( ret != 0 )
goto exit;
@ -1039,7 +1044,7 @@ int mbedtls_gcm_self_test( int verbose )
goto exit;
}
ret = mbedtls_gcm_finish( &ctx, tag_buf, 16 );
ret = mbedtls_gcm_finish( &ctx, NULL, 0, tag_buf, 16 );
if( ret != 0 )
goto exit;