Remove last use of non-bit operations

According to https://www.bearssl.org/ctmul.html even single-precision multiplication is not constant-time on some older platforms. An added benefit of the new code is that it removes the somewhat mysterious constant 0x1ff - which was selected because at that point the maximum value of padlen was 256. The new code is perhaps a bit more readable for that reason. Signed-off-by: Manuel Pégourié-Gonnard <[email protected]>
Mbed-TLS · Sep 18, 2020 · 822b372 · 822b372
1 parent 2a59fb4
commit 822b372
Showing 1 changed file with 1 addition and 1 deletion.
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
@@ -1679,7 +1679,7 @@ int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
             if( padlen > 0 && correct == 0 )
                 MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad padding byte detected" ) );
 #endif
-            padlen &= correct * 0x1FF;
+            padlen &= mbedtls_ssl_cf_mask_from_bit( correct );
         }
         else
 #endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \