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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_oaep_encode.c
OAEP Padding for LTC_PKCS #1, Tom St Denis
*/
#ifdef LTC_PKCS_1
/**
LTC_PKCS #1 v2.00 OAEP encode
@param msg The data to encode
@param msglen The length of the data to encode (octets)
@param lparam A session or system parameter (can be NULL)
@param lparamlen The length of the lparam data
@param modulus_bitlen The bit length of the RSA modulus
@param prng An active PRNG state
@param prng_idx The index of the PRNG desired
@param hash_idx The index of the hash desired
@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_oaep_encode(const unsigned char *msg, unsigned long msglen,
const unsigned char *lparam, unsigned long lparamlen,
unsigned long modulus_bitlen, prng_state *prng,
int prng_idx, int hash_idx,
unsigned char *out, unsigned long *outlen)
{
unsigned char *DB, *seed, *mask;
unsigned long hLen, x, y, modulus_len;
int err;
LTC_ARGCHK(msg != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
/* test valid hash */
if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
return err;
}
/* valid prng */
if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {
return err;
}
hLen = hash_descriptor[hash_idx].hashsize;
modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
/* test message size */
if ((2*hLen >= (modulus_len - 2)) || (msglen > (modulus_len - 2*hLen - 2))) {
return CRYPT_PK_INVALID_SIZE;
}
/* allocate ram for DB/mask/salt of size modulus_len */
DB = XMALLOC(modulus_len);
mask = XMALLOC(modulus_len);
seed = XMALLOC(hLen);
if (DB == NULL || mask == NULL || seed == NULL) {
if (DB != NULL) {
XFREE(DB);
}
if (mask != NULL) {
XFREE(mask);
}
if (seed != NULL) {
XFREE(seed);
}
return CRYPT_MEM;
}
/* get lhash */
/* DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */
x = modulus_len;
if (lparam != NULL) {
if ((err = hash_memory(hash_idx, lparam, lparamlen, DB, &x)) != CRYPT_OK) {
goto LBL_ERR;
}
} else {
/* can't pass hash_memory a NULL so use DB with zero length */
if ((err = hash_memory(hash_idx, DB, 0, DB, &x)) != CRYPT_OK) {
goto LBL_ERR;
}
}
/* append PS then 0x01 (to lhash) */
x = hLen;
y = modulus_len - msglen - 2*hLen - 2;
XMEMSET(DB+x, 0, y);
x += y;
/* 0x01 byte */
DB[x++] = 0x01;
/* message (length = msglen) */
XMEMCPY(DB+x, msg, msglen);
x += msglen;
/* now choose a random seed */
if (prng_descriptor[prng_idx].read(seed, hLen, prng) != hLen) {
err = CRYPT_ERROR_READPRNG;
goto LBL_ERR;
}
/* compute MGF1 of seed (k - hlen - 1) */
if ((err = pkcs_1_mgf1(hash_idx, seed, hLen, mask, modulus_len - hLen - 1)) != CRYPT_OK) {
goto LBL_ERR;
}
/* xor against DB */
for (y = 0; y < (modulus_len - hLen - 1); y++) {
DB[y] ^= mask[y];
}
/* compute MGF1 of maskedDB (hLen) */
if ((err = pkcs_1_mgf1(hash_idx, DB, modulus_len - hLen - 1, mask, hLen)) != CRYPT_OK) {
goto LBL_ERR;
}
/* XOR against seed */
for (y = 0; y < hLen; y++) {
seed[y] ^= mask[y];
}
/* create string of length modulus_len */
if (*outlen < modulus_len) {
*outlen = modulus_len;
err = CRYPT_BUFFER_OVERFLOW;
goto LBL_ERR;
}
/* start output which is 0x00 || maskedSeed || maskedDB */
x = 0;
out[x++] = 0x00;
XMEMCPY(out+x, seed, hLen);
x += hLen;
XMEMCPY(out+x, DB, modulus_len - hLen - 1);
x += modulus_len - hLen - 1;
*outlen = x;
err = CRYPT_OK;
LBL_ERR:
#ifdef LTC_CLEAN_STACK
zeromem(DB, modulus_len);
zeromem(seed, hLen);
zeromem(mask, modulus_len);
#endif
XFREE(seed);
XFREE(mask);
XFREE(DB);
return err;
}
#endif /* LTC_PKCS_1 */
/* $Source$ */
/* $Revision$ */
/* $Date$ */
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