code: func Verify(sm *SignedManifest) ([]libtrust.PublicKey, error) {
  	js, err := libtrust.ParsePrettySignature(sm.all, "signatures")
  	if err != nil {
  		logrus.WithField("err", err).Debugf("(*SignedManifest).Verify")
  		return nil, err
  	}
  
  	return js.Verify()
  }
docs: // Verify verifies the signature of the signed manifest returning the public
  // keys used during signing.