diff options
Diffstat (limited to 'src/pk/ecc/ecc_decrypt_key.c')
| -rw-r--r-- | src/pk/ecc/ecc_decrypt_key.c | 150 |
1 files changed, 150 insertions, 0 deletions
diff --git a/src/pk/ecc/ecc_decrypt_key.c b/src/pk/ecc/ecc_decrypt_key.c new file mode 100644 index 0000000..bb56208 --- /dev/null +++ b/src/pk/ecc/ecc_decrypt_key.c @@ -0,0 +1,150 @@ +/* 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 $ */ + |