| // SPDX-License-Identifier: BSD-2-Clause |
| /* 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. |
| */ |
| |
| #include "tomcrypt_private.h" |
| |
| #ifdef LTC_MDH |
| |
| /** |
| Create a DH shared secret. |
| @param private_key The private DH key in the pair |
| @param public_key The public DH key in the pair |
| @param out [out] The destination of the shared data |
| @param outlen [in/out] The max size and resulting size of the shared data. |
| @return CRYPT_OK if successful |
| */ |
| int dh_shared_secret(const dh_key *private_key, const dh_key *public_key, |
| unsigned char *out, unsigned long *outlen) |
| { |
| void *tmp; |
| unsigned long x; |
| int err; |
| |
| LTC_ARGCHK(private_key != NULL); |
| LTC_ARGCHK(public_key != NULL); |
| LTC_ARGCHK(out != NULL); |
| LTC_ARGCHK(outlen != NULL); |
| |
| /* types valid? */ |
| if (private_key->type != PK_PRIVATE) { |
| return CRYPT_PK_NOT_PRIVATE; |
| } |
| |
| /* same DH group? */ |
| if (mp_cmp(private_key->prime, public_key->prime) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; } |
| if (mp_cmp(private_key->base, public_key->base) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; } |
| |
| /* init big numbers */ |
| if ((err = mp_init(&tmp)) != CRYPT_OK) { |
| return err; |
| } |
| |
| /* check public key */ |
| if ((err = dh_check_pubkey(public_key)) != CRYPT_OK) { |
| goto error; |
| } |
| |
| /* compute tmp = y^x mod p */ |
| if ((err = mp_exptmod(public_key->y, private_key->x, private_key->prime, tmp)) != CRYPT_OK) { |
| goto error; |
| } |
| |
| /* enough space for output? */ |
| x = (unsigned long)mp_unsigned_bin_size(tmp); |
| if (*outlen < x) { |
| *outlen = x; |
| err = CRYPT_BUFFER_OVERFLOW; |
| goto error; |
| } |
| if ((err = mp_to_unsigned_bin(tmp, out)) != CRYPT_OK) { |
| goto error; |
| } |
| *outlen = x; |
| err = CRYPT_OK; |
| |
| error: |
| mp_clear(tmp); |
| return err; |
| } |
| |
| #endif /* LTC_MDH */ |
| |
| /* ref: $Format:%D$ */ |
| /* git commit: $Format:%H$ */ |
| /* commit time: $Format:%ai$ */ |