// RFC 7836 VKO GOST R 34.10-2012 256-bit key agreement function.
// UKM is user keying material, also called VKO-factor.
func (prv *PrivateKey) KEK2012256(pub *PublicKey, ukm *big.Int) ([]byte, error) {
// RFC 7836 VKO GOST R 34.10-2012 256-bit key agreement function.
// UKM is user keying material, also called VKO-factor.
func (prv *PrivateKey) KEK2012256(pub *PublicKey, ukm *big.Int) ([]byte, error) {