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Make GCM tag check "constant-time"

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Manuel Pégourié-Gonnard 2013-08-31 16:37:46 +02:00
parent 07f8fa5a69
commit 20d6a17af9
1 changed files with 11 additions and 4 deletions
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15
library/gcm.c
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@ -357,15 +357,22 @@ int gcm_auth_decrypt( gcm_context *ctx,
unsigned char *output )
{
unsigned char check_tag[16];
size_t i;
int diff;
gcm_crypt_and_tag( ctx, GCM_DECRYPT, length, iv, iv_len, add, add_len, input, output, tag_len, check_tag );
if( memcmp( check_tag, tag, tag_len ) == 0 )
return( 0 );
/* Check tag in "constant-time" */
for( diff = 0, i = 0; i < tag_len; i++ )
diff |= tag[i] ^ check_tag[i];
memset( output, 0, length );
if( diff != 0 )
{
memset( output, 0, length );
return( POLARSSL_ERR_GCM_AUTH_FAILED );
}
return( POLARSSL_ERR_GCM_AUTH_FAILED );
return( 0 );
}
#if defined(POLARSSL_SELF_TEST)