/* 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.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(dh_key *private_key, 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: $Format:%ai$ */