136 lines
3.5 KiB
C
136 lines
3.5 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://libtomcrypt.org
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*/
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#include "mycrypt.h"
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/* OAEP Padding for PKCS #1 -- Tom St Denis */
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#ifdef PKCS_1
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int pkcs_1_oaep_decode(const unsigned char *msg, unsigned long msglen,
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const unsigned char *lparam, unsigned long lparamlen,
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unsigned long modulus_bitlen, int hash_idx,
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unsigned char *out, unsigned long *outlen)
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{
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unsigned char DB[1024], seed[MAXBLOCKSIZE], mask[sizeof(DB)];
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unsigned long hLen, x, y, modulus_len;
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int err;
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_ARGCHK(msg != NULL);
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_ARGCHK(out != NULL);
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_ARGCHK(outlen != NULL);
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/* test valid hash */
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if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
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return err;
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}
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hLen = hash_descriptor[hash_idx].hashsize;
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modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
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/* test message size */
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if (modulus_len >= sizeof(DB) || msglen != modulus_len) {
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return CRYPT_PK_INVALID_SIZE;
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}
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/* ok so it's now in the form
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0x00 || maskedseed || maskedDB
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1 || hLen || modulus_len - hLen - 1
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*/
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/* must have leading 0x00 byte */
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if (msg[0] != 0x00) {
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return CRYPT_INVALID_PACKET;
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}
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/* now read the masked seed */
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for (x = 1, y = 0; y < hLen; y++) {
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seed[y] = msg[x++];
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}
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/* now read the masked DB */
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for (y = 0; y < modulus_len - hLen - 1; y++) {
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DB[y] = msg[x++];
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}
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/* compute MGF1 of maskedDB (hLen) */
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if ((err = pkcs_1_mgf1(DB, modulus_len - hLen - 1, hash_idx, mask, hLen)) != CRYPT_OK) {
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return err;
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}
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/* XOR against seed */
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for (y = 0; y < hLen; y++) {
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seed[y] ^= mask[y];
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}
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/* compute MGF1 of seed (k - hlen - 1) */
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if ((err = pkcs_1_mgf1(seed, hLen, hash_idx, mask, modulus_len - hLen - 1)) != CRYPT_OK) {
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return err;
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}
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/* xor against DB */
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for (y = 0; y < (modulus_len - hLen - 1); y++) {
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DB[y] ^= mask[y];
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}
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/* now DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */
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/* compute lhash and store it in seed [reuse temps!] */
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x = sizeof(seed);
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if (lparam != NULL) {
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if ((err = hash_memory(hash_idx, lparam, lparamlen, seed, &x)) != CRYPT_OK) {
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return err;
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}
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} else {
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/* can't pass hash_memory a NULL so use DB with zero length */
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if ((err = hash_memory(hash_idx, DB, 0, seed, &x)) != CRYPT_OK) {
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return err;
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}
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}
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/* compare the lhash'es */
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if (memcmp(seed, DB, hLen) != 0) {
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return CRYPT_INVALID_PACKET;
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}
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/* now zeroes before a 0x01 */
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for (x = hLen; x < (modulus_len - hLen - 1) && DB[x] == 0x00; x++) {
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/* step... */
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}
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/* error out if wasn't 0x01 */
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if (x == (modulus_len - hLen - 1) || DB[x] != 0x01) {
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return CRYPT_INVALID_PACKET;
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}
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/* rest is the message (and skip 0x01) */
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if (msglen - ++x > *outlen) {
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return CRYPT_BUFFER_OVERFLOW;
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}
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/* copy message */
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*outlen = (modulus_len - hLen - 1) - x;
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for (y = 0; x != (modulus_len - hLen - 1); ) {
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out[y++] = DB[x++];
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}
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#ifdef CLEAN_STACK
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zeromem(DB, sizeof(DB));
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zeromem(seed, sizeof(seed));
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zeromem(mask, sizeof(mask));
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#endif
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return CRYPT_OK;
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}
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#endif /* PKCS_1 */
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