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use CT interface in add_zeros_and_len_padding()

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Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
This commit is contained in:
Dave Rodgman
2023-09-18 21:51:55 +01:00
parent 6b7e2a5809
commit 6cec41c3bb
1 changed files with 8 additions and 5 deletions
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13
library/cipher.c
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@ -935,7 +935,8 @@ static int get_zeros_and_len_padding(unsigned char *input, size_t input_len,
size_t *data_len) size_t *data_len)
{ {
size_t i, pad_idx; 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) { if (NULL == input || NULL == data_len) {
return MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA; 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; *data_len = input_len - padding_len;
/* Avoid logical || since it results in a branch */ /* Avoid logical || since it results in a branch */
bad |= padding_len > input_len; bad = mbedtls_ct_uint_gt(padding_len, input_len);
bad |= padding_len == 0; bad = mbedtls_ct_bool_or(bad, mbedtls_ct_uint_eq(padding_len, 0));
/* The number of bytes checked must be independent of padding_len */ /* The number of bytes checked must be independent of padding_len */
pad_idx = input_len - padding_len; pad_idx = input_len - padding_len;
for (i = 0; i < input_len - 1; i++) { 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 */ #endif /* MBEDTLS_CIPHER_PADDING_ZEROS_AND_LEN */