code: func ToPrivateKey(keyB64 Base64String, auth string) (*ecdsa.PrivateKey, error) {
  	keyjson, err := ToBytes(keyB64)
  	if err != nil {
  		return nil, err
  	}
  	key, err := keystore.DecryptKey(keyjson, auth)
  	if err != nil {
  		return nil, err
  	}
  	return key.PrivateKey, nil
  }
docs: // ToPrivateKey returns decrypted *ecdsa.PrivateKey from base64 of encrypted keystore.Key.