/* 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@iahu.ca, http://libtomcrypt.org */ #include "mycrypt.h" /* OAEP Padding for PKCS #1 -- Tom St Denis */ #ifdef PKCS_1 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) { unsigned char DB[1024], seed[MAXBLOCKSIZE], mask[sizeof(DB)]; unsigned long hLen, x, y, modulus_len; int err; _ARGCHK(msg != NULL); _ARGCHK(out != NULL); _ARGCHK(outlen != NULL); /* 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 message size */ if (modulus_len >= sizeof(DB) || msglen != modulus_len) { return CRYPT_PK_INVALID_SIZE; } /* 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) { return CRYPT_INVALID_PACKET; } /* now read the masked seed */ for (x = 1, y = 0; y < hLen; y++) { seed[y] = msg[x++]; } /* now read the masked DB */ for (y = 0; y < modulus_len - hLen - 1; y++) { DB[y] = msg[x++]; } /* compute MGF1 of maskedDB (hLen) */ if ((err = pkcs_1_mgf1(DB, modulus_len - hLen - 1, hash_idx, mask, hLen)) != CRYPT_OK) { return 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) { return 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 = sizeof(seed); if (lparam != NULL) { if ((err = hash_memory(hash_idx, lparam, lparamlen, seed, &x)) != CRYPT_OK) { return 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) { return err; } } /* compare the lhash'es */ if (memcmp(seed, DB, hLen) != 0) { return CRYPT_INVALID_PACKET; } /* 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) { return CRYPT_INVALID_PACKET; } /* rest is the message (and skip 0x01) */ if (msglen - ++x > *outlen) { return CRYPT_BUFFER_OVERFLOW; } /* copy message */ *outlen = (modulus_len - hLen - 1) - x; for (y = 0; x != (modulus_len - hLen - 1); ) { out[y++] = DB[x++]; } #ifdef CLEAN_STACK zeromem(DB, sizeof(DB)); zeromem(seed, sizeof(seed)); zeromem(mask, sizeof(mask)); #endif return CRYPT_OK; } #endif /* PKCS_1 */