| /* 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.org |
| */ |
| #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(DB, modulus_len - hLen - 1, hash_idx, 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(seed, hLen, hash_idx, 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 (memcmp(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_OK; |
| goto LBL_ERR; |
| } |
| |
| /* rest is the message (and skip 0x01) */ |
| if ((modulus_len - hLen - 1) - ++x > *outlen) { |
| 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: 1.5 $ */ |
| /* $Date: 2005/06/18 02:37:06 $ */ |