code: func Keypair(rand io.Reader) (publicKey PublicKey, privateKey PrivateKey, err error) {
  	public, private, err := ed25519.GenerateKey(rand)
  	if err != nil {
  		return nil, nil, err
  	}
  	return PublicKey(public), PrivateKey(private), nil
  }
docs: // Keypair generates a public/private key pair using entropy from rand.
  // If rand is nil, crypto/rand.Reader will be used.