code: func (prv *PrivateKey) ExportECDSA() *ecdsa.PrivateKey {
  	pub := &prv.PublicKey
  	pubECDSA := pub.ExportECDSA()
  	return &ecdsa.PrivateKey{PublicKey: *pubECDSA, D: prv.D}
  }
docs: // Export an ECIES private key as an ECDSA private key.