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CT fix for get_pkcs_padding

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Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
This commit is contained in:
Dave Rodgman
2023-09-20 14:29:45 +01:00
parent 40dc3b3727
commit 9f3f73d212
1 changed files with 4 additions and 3 deletions
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7
library/cipher.c
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@@ -30,6 +30,7 @@
#include "mbedtls/platform_util.h" #include "mbedtls/platform_util.h"
#include "mbedtls/error.h" #include "mbedtls/error.h"
#include "mbedtls/constant_time.h" #include "mbedtls/constant_time.h"
#include "constant_time_internal.h"
#include <stdlib.h> #include <stdlib.h>
#include <string.h> #include <string.h>
@@ -755,10 +756,10 @@ static int get_pkcs_padding(unsigned char *input, size_t input_len,
* so pick input_len, which is usually 8 or 16 (one block) */ * so pick input_len, which is usually 8 or 16 (one block) */
pad_idx = input_len - padding_len; pad_idx = input_len - padding_len;
for (i = 0; i < input_len; i++) { for (i = 0; i < input_len; i++) {
bad |= (input[i] ^ padding_len) * (i >= pad_idx); size_t mask = mbedtls_ct_size_mask_ge(i, pad_idx);
bad |= (input[i] ^ padding_len) & mask;
} }
return (int) mbedtls_ct_uint_if(bad, MBEDTLS_ERR_CIPHER_INVALID_PADDING, 0);
return MBEDTLS_ERR_CIPHER_INVALID_PADDING * (bad != 0);
} }
#endif /* MBEDTLS_CIPHER_PADDING_PKCS7 */ #endif /* MBEDTLS_CIPHER_PADDING_PKCS7 */