code: func (pka PublicKeyAlgorithm) CanSign() bool {
  	switch pka {
  	case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly, PubKeyAlgoDSA:
  		return true
  	}
  	return false
  }
docs: // CanSign returns true if it's possible for a public key of the given type to
  // sign a message.