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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
*/
#include "tomcrypt.h"
/** @file pkcs_1_v1_5_decode.c
*
* PKCS #1 v1.5 Padding. (Andreas Lange)
*/
#ifdef PKCS_1
/** @brief PKCS #1 v1.5 decode.
*
* @param msg The encoded data to decode
* @param msglen The length of the encoded data (octets)
* @param block_type Block type to use in padding (\sa ltc_pkcs_1_v1_5_blocks)
* @param modulus_bitlen The bit length of the RSA modulus
* @param out [out] Destination of decoding
* @param outlen [in/out] The max size and resulting size of the decoding
* @param is_valid [out] Boolean whether the padding was valid
*
* @return CRYPT_OK if successful (even if invalid)
*/
int pkcs_1_v1_5_decode(const unsigned char *msg,
unsigned long msglen,
int block_type,
unsigned long modulus_bitlen,
unsigned char *out,
unsigned long *outlen,
int *is_valid)
{
unsigned long modulus_len, ps_len, i;
int result;
/* default to invalid packet */
*is_valid = 0;
modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
/* test message size */
if ((msglen > modulus_len) || (modulus_len < 11)) {
return CRYPT_PK_INVALID_SIZE;
}
/* separate encoded message */
if ((msg[0] != 0x00) || (msg[1] != (unsigned char)block_type)) {
result = CRYPT_INVALID_PACKET;
goto bail;
}
if (block_type == LTC_PKCS_1_EME) {
for (i = 2; i < modulus_len; i++) {
/* separator */
if (msg[i] == 0x00) { break; }
}
ps_len = i++ - 2;
if ((i >= modulus_len) || (ps_len < 8)) {
/* There was no octet with hexadecimal value 0x00 to separate ps from m,
* or the length of ps is less than 8 octets.
*/
result = CRYPT_INVALID_PACKET;
goto bail;
}
} else {
for (i = 2; i < modulus_len - 1; i++) {
if (msg[i] != 0xFF) { break; }
}
/* separator check */
if (msg[i] != 0) {
/* There was no octet with hexadecimal value 0x00 to separate ps from m. */
result = CRYPT_INVALID_PACKET;
goto bail;
}
ps_len = i - 2;
}
if (*outlen < (msglen - (2 + ps_len + 1))) {
*outlen = msglen - (2 + ps_len + 1);
result = CRYPT_BUFFER_OVERFLOW;
goto bail;
}
*outlen = (msglen - (2 + ps_len + 1));
XMEMCPY(out, &msg[2 + ps_len + 1], *outlen);
/* valid packet */
*is_valid = 1;
result = CRYPT_OK;
bail:
return result;
} /* pkcs_1_v1_5_decode */
#endif /* #ifdef PKCS_1 */
/* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_v1_5_decode.c,v $ */
/* $Revision: 1.5 $ */
/* $Date: 2006/12/16 17:41:21 $ */
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