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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_oaep_decode.c
OAEP Padding for PKCS #1, Tom St Denis
*/
#ifdef PKCS_1
/**
PKCS #1 v2.00 OAEP decode
@param msg The encoded data to decode
@param msglen The length of the encoded data (octets)
@param lparam The session or system data (can be NULL)
@param lparamlen The length of the lparam
@param modulus_bitlen The bit length of the RSA modulus
@param hash_idx The index of the hash desired
@param out [out] Destination of decoding
@param outlen [in/out] The max size and resulting size of the decoding
@param res [out] Result of decoding, 1==valid, 0==invalid
@return CRYPT_OK if successful (even if invalid)
*/
int pkcs_1_oaep_decode(const unsigned char *msg, unsigned long msglen,
const unsigned char *lparam, unsigned long lparamlen,
unsigned long modulus_bitlen, int hash_idx,
unsigned char *out, unsigned long *outlen,
int *res)
{
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);
LTC_ARGCHK(res != NULL);
/* default to invalid packet */
*res = 0;
/* test valid hash */
if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
return err;
}
hLen = hash_descriptor[hash_idx].hashsize;
modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
/* test hash/message size */
if ((2*hLen >= (modulus_len - 2)) || (msglen != modulus_len)) {
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;
}
/* ok so it's now in the form
0x00 || maskedseed || maskedDB
1 || hLen || modulus_len - hLen - 1
*/
/* must have leading 0x00 byte */
if (msg[0] != 0x00) {
err = CRYPT_OK;
goto LBL_ERR;
}
/* now read the masked seed */
x = 1;
XMEMCPY(seed, msg + x, hLen);
x += hLen;
/* now read the masked DB */
XMEMCPY(DB, msg + x, modulus_len - hLen - 1);
x += modulus_len - hLen - 1;
/* 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];
}
/* 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];
}
/* now DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */
/* compute lhash and store it in seed [reuse temps!] */
x = modulus_len;
if (lparam != NULL) {
if ((err = hash_memory(hash_idx, lparam, lparamlen, seed, &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, seed, &x)) != CRYPT_OK) {
goto LBL_ERR;
}
}
/* compare the lhash'es */
if (XMEMCMP(seed, DB, hLen) != 0) {
err = CRYPT_OK;
goto LBL_ERR;
}
/* now zeroes before a 0x01 */
for (x = hLen; x < (modulus_len - hLen - 1) && DB[x] == 0x00; x++) {
/* step... */
}
/* error out if wasn't 0x01 */
if (x == (modulus_len - hLen - 1) || DB[x] != 0x01) {
err = CRYPT_INVALID_PACKET;
goto LBL_ERR;
}
/* rest is the message (and skip 0x01) */
if ((modulus_len - hLen - 1 - ++x) > *outlen) {
*outlen = modulus_len - hLen - 1 - x;
err = CRYPT_BUFFER_OVERFLOW;
goto LBL_ERR;
}
/* copy message */
*outlen = modulus_len - hLen - 1 - x;
XMEMCPY(out, DB + x, modulus_len - hLen - 1 - x);
x += modulus_len - hLen - 1;
/* valid packet */
*res = 1;
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 /* PKCS_1 */
/* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_oaep_decode.c,v $ */
/* $Revision: 1.11 $ */
/* $Date: 2006/11/01 09:28:17 $ */
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