code: func NewRSAVerifier() Verifier {
  	return verifyFn(func(checksum, signature []byte, hash crypto.Hash, publicKey crypto.PublicKey) error {
  		key, ok := publicKey.(*rsa.PublicKey)
  		if !ok {
  			return errors.New("not a valid RSA public key")
  		}
  		return rsa.VerifyPKCS1v15(key, hash, checksum, signature)
  	})
  }
docs: // NewRSAVerifier returns a Verifier that uses the RSA algorithm to verify updates.