diff --git a/library/cipher.c b/library/cipher.c index 41cd96f78..6fe72052e 100644 --- a/library/cipher.c +++ b/library/cipher.c @@ -935,7 +935,8 @@ static int get_zeros_and_len_padding(unsigned char *input, size_t input_len, size_t *data_len) { size_t i, pad_idx; - unsigned char padding_len, bad = 0; + unsigned char padding_len; + mbedtls_ct_condition_t bad; if (NULL == input || NULL == data_len) { return MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA; @@ -945,16 +946,18 @@ static int get_zeros_and_len_padding(unsigned char *input, size_t input_len, *data_len = input_len - padding_len; /* Avoid logical || since it results in a branch */ - bad |= padding_len > input_len; - bad |= padding_len == 0; + bad = mbedtls_ct_uint_gt(padding_len, input_len); + bad = mbedtls_ct_bool_or(bad, mbedtls_ct_uint_eq(padding_len, 0)); /* The number of bytes checked must be independent of padding_len */ pad_idx = input_len - padding_len; for (i = 0; i < input_len - 1; i++) { - bad |= input[i] * (i >= pad_idx); + mbedtls_ct_condition_t is_padding = mbedtls_ct_uint_ge(i, pad_idx); + mbedtls_ct_condition_t nonzero_pad_byte = mbedtls_ct_uint_if_else_0(is_padding, mbedtls_ct_bool(input[i])); + bad = mbedtls_ct_bool_or(bad, nonzero_pad_byte); } - 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_ZEROS_AND_LEN */