Use CT interface in get_one_and_zeros_padding
Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/cipher.c b/library/cipher.c
index 6fe7205..469f1b0 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -894,24 +894,28 @@
static int get_one_and_zeros_padding(unsigned char *input, size_t input_len,
size_t *data_len)
{
- size_t i;
- unsigned char done = 0, prev_done, bad;
-
if (NULL == input || NULL == data_len) {
return MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA;
}
- bad = 0x80;
+ mbedtls_ct_condition_t in_padding = MBEDTLS_CT_TRUE;
+ mbedtls_ct_condition_t bad = MBEDTLS_CT_TRUE;
+
*data_len = 0;
- for (i = input_len; i > 0; i--) {
- prev_done = done;
- done |= (input[i - 1] != 0);
- *data_len |= (i - 1) * (done != prev_done);
- bad ^= input[i - 1] * (done != prev_done);
+
+ for (int i = input_len - 1; i >= 0; i--) {
+ mbedtls_ct_condition_t is_nonzero = mbedtls_ct_bool(input[i]);
+
+ mbedtls_ct_condition_t hit_first_nonzero = mbedtls_ct_bool_and(is_nonzero, in_padding);
+
+ *data_len = mbedtls_ct_size_if(hit_first_nonzero, i, *data_len);
+
+ bad = mbedtls_ct_uint_if(hit_first_nonzero, mbedtls_ct_uint_ne(input[i], 0x80), bad);
+
+ in_padding = mbedtls_ct_bool_and(in_padding, mbedtls_ct_bool_not(is_nonzero));
}
- return MBEDTLS_ERR_CIPHER_INVALID_PADDING * (bad != 0);
-
+ return -((int) mbedtls_ct_uint_if_else_0(bad, -MBEDTLS_ERR_CIPHER_INVALID_PADDING));
}
#endif /* MBEDTLS_CIPHER_PADDING_ONE_AND_ZEROS */