commit 291f9af935e8cbe78216c93ae3b62728e4e62729
author Manuel Pégourié-Gonnard <mpg@elzevir.fr> Mon Oct 28 12:51:32 2013 +0100
committer Paul Bakker <p.j.bakker@polarssl.org> Thu Oct 31 14:22:27 2013 +0100
tree c18b78c2645bd02cafeabb51d29bca4d63dad547
parent 424cd6943c82b7efe22833125ed082f8d569fcd4

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 4c1f8ea..1239ca2 100644
--- a/programs/aes/aescrypt2.c
+++ b/programs/aes/aescrypt2.c
@@ -75,6 +75,7 @@
     unsigned char key[512];
     unsigned char digest[32];
     unsigned char buffer[1024];
+    unsigned char diff;
 
     aes_context aes_ctx;
     sha256_context sha_ctx;
@@ -397,7 +398,12 @@
             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" );