commit 79f1ff84edc219a6b3506df93763583086322e5e
author Manuel Pégourié-Gonnard <mpg@elzevir.fr> Mon Oct 28 12:51:32 2013 +0100
committer Paul Bakker <p.j.bakker@polarssl.org> Mon Jul 07 14:07:23 2014 +0200
tree ae97cc48fcf30d743bd7430f12091b574da9e757
parent 2a8c2881f4158b018011eaa77ab8cfb8761389a5

Make all hash checking in programs constant-time

programs/aes/aescrypt2.c

diff --git a/programs/aes/aescrypt2.c b/programs/aes/aescrypt2.c
index 1bc6574..f4fe48a 100644
--- a/programs/aes/aescrypt2.c
+++ b/programs/aes/aescrypt2.c
@@ -79,6 +79,7 @@
     unsigned char key[512];
     unsigned char digest[32];
     unsigned char buffer[1024];
+    unsigned char diff;
 
     aes_context aes_ctx;
     sha2_context sha_ctx;
@@ -401,7 +402,12 @@
             goto exit;
         }
 
-        if( memcmp( digest, buffer, 32 ) != 0 )
+        /* Use constant-time buffer comparison */
+        diff = 0;
+        for( i = 0; i < 32; i++ )
+            diff |= digest[i] ^ buffer[i];
+
+        if( diff != 0 )
         {
             fprintf( stderr, "HMAC check failed: wrong key, "
                              "or file corrupted.\n" );