71 lines
1.9 KiB
C
71 lines
1.9 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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#ifdef LTC_MDH
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/**
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Create a DH shared secret.
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@param private_key The private DH key in the pair
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@param public_key The public DH key in the pair
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@param out [out] The destination of the shared data
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@param outlen [in/out] The max size and resulting size of the shared data.
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@return CRYPT_OK if successful
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*/
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int dh_shared_secret(const dh_key *private_key, const dh_key *public_key,
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unsigned char *out, unsigned long *outlen)
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{
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void *tmp;
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unsigned long x;
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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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/* types 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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/* same DH group? */
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if (ltc_mp_cmp(private_key->prime, public_key->prime) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; }
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if (ltc_mp_cmp(private_key->base, public_key->base) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; }
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/* init big numbers */
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if ((err = ltc_mp_init(&tmp)) != CRYPT_OK) {
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return err;
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}
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/* check public key */
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if ((err = dh_check_pubkey(public_key)) != CRYPT_OK) {
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goto error;
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}
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/* compute tmp = y^x mod p */
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if ((err = ltc_mp_exptmod(public_key->y, private_key->x, private_key->prime, tmp)) != CRYPT_OK) {
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goto error;
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}
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/* enough space for output? */
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x = (unsigned long)ltc_mp_unsigned_bin_size(tmp);
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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 error;
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}
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if ((err = ltc_mp_to_unsigned_bin(tmp, out)) != CRYPT_OK) {
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goto error;
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}
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*outlen = x;
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err = CRYPT_OK;
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error:
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ltc_mp_clear(tmp);
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return err;
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}
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#endif /* LTC_MDH */
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