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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://libtom.org
*/
#include "tomcrypt.h"
/*! \file pkcs_1_v1_5_encode.c
*
* LTC_PKCS #1 v1.5 Padding (Andreas Lange)
*/
#ifdef LTC_PKCS_1
/*! \brief LTC_PKCS #1 v1.5 encode.
*
* \param msg The data to encode
* \param msglen The length of the data to encode (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] The destination for the encoded data
* \param outlen [in/out] The max size and resulting size of the encoded data
*
* \return CRYPT_OK if successful
*/
int pkcs_1_v1_5_encode(const unsigned char *msg,
unsigned long msglen,
int block_type,
unsigned long modulus_bitlen,
unsigned char *out, unsigned long *outlen)
{
unsigned long modulus_len, ps_len, i;
unsigned char *ps;
int result;
/* valid block_type? */
if ((block_type != LTC_LTC_PKCS_1_EMSA) &&
(block_type != LTC_LTC_PKCS_1_EME)) {
return CRYPT_PK_INVALID_PADDING;
}
modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
/* test message size */
if ((msglen + 11) > modulus_len) {
return CRYPT_PK_INVALID_SIZE;
}
if (*outlen < modulus_len) {
*outlen = modulus_len;
result = CRYPT_BUFFER_OVERFLOW;
goto bail;
}
/* generate an octets string PS */
ps = &out[2];
ps_len = modulus_len - msglen - 3;
if (block_type == LTC_LTC_PKCS_1_EME) {
/* now choose a random ps */
get_random_bytes(ps, ps_len);
/* transform zero bytes (if any) to non-zero random bytes */
for (i = 0; i < ps_len; i++) {
while (ps[i] == 0) {
get_random_bytes(&ps[i], 1);
}
}
} else {
XMEMSET(ps, 0xFF, ps_len);
}
/* create string of length modulus_len */
out[0] = 0x00;
out[1] = (unsigned char)block_type; /* block_type 1 or 2 */
out[2 + ps_len] = 0x00;
XMEMCPY(&out[2 + ps_len + 1], msg, msglen);
*outlen = modulus_len;
result = CRYPT_OK;
bail:
return result;
} /* pkcs_1_v1_5_encode */
#endif /* #ifdef LTC_PKCS_1 */
/* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_v1_5_encode.c,v $ */
/* $Revision: 1.4 $ */
/* $Date: 2007/05/12 14:32:35 $ */
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