67 lines
1.7 KiB
C
67 lines
1.7 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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#include "tomcrypt_private.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(const ecc_key *private_key, const 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, *a;
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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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/* 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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prime = private_key->dp.prime;
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a = private_key->dp.A;
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if ((err = ltc_mp.ecc_ptmul(private_key->k, &public_key->pubkey, result, a, prime, 1)) != CRYPT_OK) { goto done; }
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x = (unsigned long)ltc_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 = ltc_mp_to_unsigned_bin(result->x, out + (x - ltc_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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ltc_ecc_del_point(result);
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return err;
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}
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#endif
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