code: func VerifyChains(sm *SignedManifest, ca *x509.CertPool) ([][]*x509.Certificate, error) {
  	js, err := libtrust.ParsePrettySignature(sm.all, "signatures")
  	if err != nil {
  		return nil, err
  	}
  
  	return js.VerifyChains(ca)
  }
docs: // VerifyChains verifies the signature of the signed manifest against the
  // certificate pool returning the list of verified chains. Signatures without
  // an x509 chain are not checked.