Add countermeasure against cache-based lucky 13
diff --git a/ChangeLog b/ChangeLog
index efc06fb..fe8ea19 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -8,6 +8,8 @@
* Fix potential invalid memory read in certificate parsing, that allows a
client to crash the server remotely if client authentication is enabled
(found using Codenomicon Defensics).
+ * Add countermeasure against "Lucky 13 strikes back" cache-based attack,
+ https://dl.acm.org/citation.cfm?id=2714625
Bugfix
* Fix bug in Via Padlock support (found by Nikos Mavrogiannopoulos).
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index d90da3e..709f230 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1528,7 +1528,7 @@
* Process MAC and always update for padlen afterwards to make
* total time independent of padlen
*
- * extra_run compensates MAC check for padlen
+ * extra_run compensates MAC check for padlen
*
* Known timing attacks:
* - Lucky Thirteen (http://www.isg.rhul.ac.uk/tls/TLStiming.pdf)
@@ -1536,6 +1536,9 @@
* We use ( ( Lx + 8 ) / 64 ) to handle 'negative Lx' values
* correctly. (We round down instead of up, so -56 is the correct
* value for our calculations instead of -55)
+ *
+ * Always call the xxx_process() function at least once due to cache
+ * attacks.
*/
int j, extra_run = 0;
extra_run = ( 13 + ssl->in_msglen + padlen + 8 ) / 64 -
@@ -1550,7 +1553,7 @@
md5_hmac_update( &ctx, ssl->in_ctr, ssl->in_msglen + 13 );
md5_hmac_finish( &ctx, ssl->in_msg + ssl->in_msglen );
- for( j = 0; j < extra_run; j++ )
+ for( j = 0; j < extra_run + 1; j++ )
md5_process( &ctx, ssl->in_msg );
}
else if( ssl->transform_in->maclen == 20 )
@@ -1560,7 +1563,7 @@
sha1_hmac_update( &ctx, ssl->in_ctr, ssl->in_msglen + 13 );
sha1_hmac_finish( &ctx, ssl->in_msg + ssl->in_msglen );
- for( j = 0; j < extra_run; j++ )
+ for( j = 0; j < extra_run + 1; j++ )
sha1_process( &ctx, ssl->in_msg );
}
else if( ssl->transform_in->maclen == 32 )
@@ -1570,7 +1573,7 @@
sha2_hmac_update( &ctx, ssl->in_ctr, ssl->in_msglen + 13 );
sha2_hmac_finish( &ctx, ssl->in_msg + ssl->in_msglen );
- for( j = 0; j < extra_run; j++ )
+ for( j = 0; j < extra_run + 1; j++ )
sha2_process( &ctx, ssl->in_msg );
}
else if( ssl->transform_in->maclen != 0 )