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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_encode.c
*
* PKCS #1 v1.5 Padding (Andreas Lange)
*/
#ifdef PKCS_1
/*! \brief 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 prng An active PRNG state (only for LTC_PKCS_1_EME)
* \param prng_idx The index of the PRNG desired (only for LTC_PKCS_1_EME)
* \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,
prng_state *prng,
int prng_idx,
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_PKCS_1_EMSA) &&
(block_type != LTC_PKCS_1_EME)) {
return CRYPT_PK_INVALID_PADDING;
}
if (block_type == LTC_PKCS_1_EME) { /* encryption padding, we need a valid PRNG */
if ((result = prng_is_valid(prng_idx)) != CRYPT_OK) {
return result;
}
}
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_PKCS_1_EME) {
/* now choose a random ps */
if (prng_descriptor[prng_idx].read(ps, ps_len, prng) != ps_len) {
result = CRYPT_ERROR_READPRNG;
goto bail;
}
/* transform zero bytes (if any) to non-zero random bytes */
for (i = 0; i < ps_len; i++) {
while (ps[i] == 0) {
if (prng_descriptor[prng_idx].read(&ps[i], 1, prng) != 1) {
result = CRYPT_ERROR_READPRNG;
goto bail;
}
}
}
} 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 PKCS_1 */
/* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_v1_5_encode.c,v $ */
/* $Revision: 1.2 $ */
/* $Date: 2006/11/01 09:12:06 $ */
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