code: func (k *Keyring) GetPrimaryKey() (key []byte) {
  	k.l.Lock()
  	defer k.l.Unlock()
  
  	if len(k.keys) > 0 {
  		key = k.keys[0]
  	}
  	return
  }
docs: // GetPrimaryKey returns the key on the ring at position 0. This is the key used
  // for encrypting messages, and is the first key tried for decrypting messages.