Make get_zeros_padding() constant-time
diff --git a/library/cipher.c b/library/cipher.c
index cbbdcd5..2941f40 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -533,14 +533,19 @@
static int get_zeros_padding( unsigned char *input, size_t input_len,
size_t *data_len )
{
- unsigned char *p = input + input_len - 1;
+ size_t i;
+ unsigned char done = 0, prev_done;
+
if( NULL == input || NULL == data_len )
return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
- while( *p == 0x00 && p > input )
- --p;
-
- *data_len = *p == 0x00 ? 0 : p - input + 1;
+ *data_len = 0;
+ for( i = input_len; i > 0; i-- )
+ {
+ prev_done = done;
+ done |= ( input[i-1] != 0 );
+ *data_len |= i * ( done != prev_done );
+ }
return 0;
}