From 424cd6943c82b7efe22833125ed082f8d569fcd4 Mon Sep 17 00:00:00 2001 From: Paul Bakker Date: Thu, 31 Oct 2013 14:22:08 +0100 Subject: [PATCH] Check HMAC in constant-time in crypt_and_hash --- programs/aes/crypt_and_hash.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/programs/aes/crypt_and_hash.c b/programs/aes/crypt_and_hash.c index d2845de88..50218e164 100644 --- a/programs/aes/crypt_and_hash.c +++ b/programs/aes/crypt_and_hash.c @@ -76,6 +76,7 @@ int main( int argc, char *argv[] ) unsigned char digest[POLARSSL_MD_MAX_SIZE]; unsigned char buffer[1024]; unsigned char output[1024]; + unsigned char diff; const cipher_info_t *cipher_info; const md_info_t *md_info; @@ -476,7 +477,12 @@ int main( int argc, char *argv[] ) goto exit; } - if( memcmp( digest, buffer, md_get_size( md_info ) ) != 0 ) + /* Use constant-time buffer comparison */ + diff = 0; + for( i = 0; i < md_get_size( md_info ); i++ ) + diff |= digest[i] ^ buffer[i]; + + if( diff != 0 ) { fprintf( stderr, "HMAC check failed: wrong key, " "or file corrupted.\n" );