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94 lines
2.6 KiB
C
94 lines
2.6 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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/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
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*
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* All curves taken from NIST recommendation paper of July 1999
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* Available at http://csrc.nist.gov/cryptval/dss.htm
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*/
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#include "tomcrypt.h"
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/**
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@file ecc_shared_secret.c
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ECC Crypto, Tom St Denis
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*/
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#ifdef LTC_MECC
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/**
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Create an ECC shared secret between two keys
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@param private_key The private ECC key
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@param public_key The public key
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@param out [out] Destination of the shared secret (Conforms to EC-DH from ANSI X9.63)
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@param outlen [in/out] The max size and resulting size of the shared secret
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@return CRYPT_OK if successful
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*/
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int ecc_shared_secret(ecc_key *private_key, ecc_key *public_key,
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unsigned char *out, unsigned long *outlen)
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{
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unsigned long x;
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ecc_point *result;
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void *prime;
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int err;
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LTC_ARGCHK(private_key != NULL);
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LTC_ARGCHK(public_key != NULL);
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LTC_ARGCHK(out != NULL);
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LTC_ARGCHK(outlen != NULL);
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/* type valid? */
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if (private_key->type != PK_PRIVATE) {
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return CRYPT_PK_NOT_PRIVATE;
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}
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if (ltc_ecc_is_valid_idx(private_key->idx) == 0 || ltc_ecc_is_valid_idx(public_key->idx) == 0) {
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return CRYPT_INVALID_ARG;
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}
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if (XSTRCMP(private_key->dp->name, public_key->dp->name) != 0) {
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return CRYPT_PK_TYPE_MISMATCH;
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}
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/* make new point */
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result = ltc_ecc_new_point();
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if (result == NULL) {
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return CRYPT_MEM;
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}
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if ((err = mp_init(&prime)) != CRYPT_OK) {
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ltc_ecc_del_point(result);
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return err;
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}
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if ((err = mp_read_radix(prime, (char *)private_key->dp->prime, 16)) != CRYPT_OK) { goto done; }
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if ((err = ltc_mp.ecc_ptmul(private_key->k, &public_key->pubkey, result, prime, 1)) != CRYPT_OK) { goto done; }
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x = (unsigned long)mp_unsigned_bin_size(prime);
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if (*outlen < x) {
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*outlen = x;
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err = CRYPT_BUFFER_OVERFLOW;
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goto done;
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}
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zeromem(out, x);
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if ((err = mp_to_unsigned_bin(result->x, out + (x - mp_unsigned_bin_size(result->x)))) != CRYPT_OK) { goto done; }
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err = CRYPT_OK;
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*outlen = x;
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done:
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mp_clear(prime);
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ltc_ecc_del_point(result);
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return err;
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}
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#endif
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/* ref: HEAD -> master, tag: v1.18.2 */
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/* git commit: 7e7eb695d581782f04b24dc444cbfde86af59853 */
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/* commit time: 2018-07-01 22:49:01 +0200 */
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