| /* 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 |
| */ |
| |
| /* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b |
| * |
| * All curves taken from NIST recommendation paper of July 1999 |
| * Available at http://csrc.nist.gov/cryptval/dss.htm |
| */ |
| #include "tomcrypt.h" |
| |
| /** |
| @file ecc_decrypt_key.c |
| ECC Crypto, Tom St Denis |
| */ |
| |
| #ifdef MECC |
| |
| /** |
| Decrypt an ECC encrypted key |
| @param in The ciphertext |
| @param inlen The length of the ciphertext (octets) |
| @param out [out] The plaintext |
| @param outlen [in/out] The max size and resulting size of the plaintext |
| @param key The corresponding private ECC key |
| @return CRYPT_OK if successful |
| */ |
| int ecc_decrypt_key(const unsigned char *in, unsigned long inlen, |
| unsigned char *out, unsigned long *outlen, |
| ecc_key *key) |
| { |
| unsigned char *ecc_shared, *skey, *pub_expt; |
| unsigned long x, y, hashOID[32]; |
| int hash, err; |
| ecc_key pubkey; |
| ltc_asn1_list decode[3]; |
| |
| LTC_ARGCHK(in != NULL); |
| LTC_ARGCHK(out != NULL); |
| LTC_ARGCHK(outlen != NULL); |
| LTC_ARGCHK(key != NULL); |
| |
| /* right key type? */ |
| if (key->type != PK_PRIVATE) { |
| return CRYPT_PK_NOT_PRIVATE; |
| } |
| |
| /* decode to find out hash */ |
| LTC_SET_ASN1(decode, 0, LTC_ASN1_OBJECT_IDENTIFIER, hashOID, sizeof(hashOID)/sizeof(hashOID[0])); |
| |
| if ((err = der_decode_sequence(in, inlen, decode, 1)) != CRYPT_OK) { |
| return err; |
| } |
| |
| hash = find_hash_oid(hashOID, decode[0].size); |
| if (hash_is_valid(hash) != CRYPT_OK) { |
| return CRYPT_INVALID_PACKET; |
| } |
| |
| /* we now have the hash! */ |
| |
| /* allocate memory */ |
| pub_expt = XMALLOC(ECC_BUF_SIZE); |
| ecc_shared = XMALLOC(ECC_BUF_SIZE); |
| skey = XMALLOC(MAXBLOCKSIZE); |
| if (pub_expt == NULL || ecc_shared == NULL || skey == NULL) { |
| if (pub_expt != NULL) { |
| XFREE(pub_expt); |
| } |
| if (ecc_shared != NULL) { |
| XFREE(ecc_shared); |
| } |
| if (skey != NULL) { |
| XFREE(skey); |
| } |
| return CRYPT_MEM; |
| } |
| LTC_SET_ASN1(decode, 1, LTC_ASN1_OCTET_STRING, pub_expt, ECC_BUF_SIZE); |
| LTC_SET_ASN1(decode, 2, LTC_ASN1_OCTET_STRING, skey, MAXBLOCKSIZE); |
| |
| /* read the structure in now */ |
| if ((err = der_decode_sequence(in, inlen, decode, 3)) != CRYPT_OK) { |
| goto LBL_ERR; |
| } |
| |
| /* import ECC key from packet */ |
| if ((err = ecc_import(decode[1].data, decode[1].size, &pubkey)) != CRYPT_OK) { |
| goto LBL_ERR; |
| } |
| |
| /* make shared key */ |
| x = ECC_BUF_SIZE; |
| if ((err = ecc_shared_secret(key, &pubkey, ecc_shared, &x)) != CRYPT_OK) { |
| ecc_free(&pubkey); |
| goto LBL_ERR; |
| } |
| ecc_free(&pubkey); |
| |
| y = MIN(ECC_BUF_SIZE, MAXBLOCKSIZE); |
| if ((err = hash_memory(hash, ecc_shared, x, ecc_shared, &y)) != CRYPT_OK) { |
| goto LBL_ERR; |
| } |
| |
| /* ensure the hash of the shared secret is at least as big as the encrypt itself */ |
| if (decode[2].size > y) { |
| err = CRYPT_INVALID_PACKET; |
| goto LBL_ERR; |
| } |
| |
| /* avoid buffer overflow */ |
| if (*outlen < decode[2].size) { |
| *outlen = decode[2].size; |
| err = CRYPT_BUFFER_OVERFLOW; |
| goto LBL_ERR; |
| } |
| |
| /* Decrypt the key */ |
| for (x = 0; x < decode[2].size; x++) { |
| out[x] = skey[x] ^ ecc_shared[x]; |
| } |
| *outlen = x; |
| |
| err = CRYPT_OK; |
| LBL_ERR: |
| #ifdef LTC_CLEAN_STACK |
| zeromem(pub_expt, ECC_BUF_SIZE); |
| zeromem(ecc_shared, ECC_BUF_SIZE); |
| zeromem(skey, MAXBLOCKSIZE); |
| #endif |
| |
| XFREE(pub_expt); |
| XFREE(ecc_shared); |
| XFREE(skey); |
| |
| return err; |
| } |
| |
| #endif |
| |
| /* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_decrypt_key.c,v $ */ |
| /* $Revision: 1.5 $ */ |
| /* $Date: 2006/06/16 21:53:41 $ */ |
| |