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Use CT interface in get_pkcs_padding

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Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
This commit is contained in:
Dave Rodgman
2023-09-18 19:00:44 +01:00
parent b4e6b41aa0
commit 6b7e2a5809
1 changed files with 9 additions and 6 deletions
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15
library/cipher.c
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@@ -30,6 +30,7 @@
#include "mbedtls/platform_util.h"
#include "mbedtls/error.h"
#include "mbedtls/constant_time.h"
#include "constant_time_internal.h"
#include <stdlib.h>
#include <string.h>
@@ -848,7 +849,8 @@ static int get_pkcs_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 = MBEDTLS_CT_FALSE;
if (NULL == input || NULL == data_len) {
return MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA;
@@ -857,18 +859,19 @@ static int get_pkcs_padding(unsigned char *input, size_t input_len,
padding_len = input[input_len - 1];
*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,
* so pick input_len, which is usually 8 or 16 (one block) */
pad_idx = input_len - padding_len;
for (i = 0; i < input_len; i++) {
bad |= (input[i] ^ padding_len) * (i >= pad_idx);
mbedtls_ct_condition_t dont_ignore = mbedtls_ct_uint_ge(i, pad_idx);
mbedtls_ct_condition_t different = mbedtls_ct_uint_ne(input[i], padding_len);
bad = mbedtls_ct_bool_or(bad, mbedtls_ct_bool_and(dont_ignore, different));
}
return MBEDTLS_ERR_CIPHER_INVALID_PADDING * (bad != 0);
return mbedtls_ct_uint_if_else_0(bad, MBEDTLS_ERR_CIPHER_INVALID_PADDING);
}
#endif /* MBEDTLS_CIPHER_PADDING_PKCS7 */