func PrvKeyFromBytes(key []byte) *PrvKey {
	curve := secp256k1.SECP256K1()
	x, y := curve.ScalarBaseMult(key)
	priv := &ecdsa.PrivateKey{
		PublicKey: ecdsa.PublicKey{
			Curve: curve,
			X:     x,
			Y:     y,
		},
		D: new(big.Int).SetBytes(key),
	}
	return (*PrvKey)(priv)
}
PrvKeyFromBytes -- returns a private and public key for secp256k1 curve.
package xcrypto
import (
	"bytes"
	"crypto/ecdsa"
	"math/big"
	"github.com/keyfuse/tokucore/xcrypto/secp256k1"
)
const (
	PrvKeyBytesLen = 32
)
type PrvKey ecdsa.PrivateKey