code: func (pk *PublicKey) VerifyKeySignature(signed *PublicKey, sig *Signature) (err error) {
  	h, err := keySignatureHash(pk, signed, sig.Hash)
  	if err != nil {
  		return err
  	}
  	return pk.VerifySignature(h, sig)
  }
docs: // VerifyKeySignature returns nil iff sig is a valid signature, made by this
  // public key, of signed.