code: func (p *Pubring) Export(id string) ([]byte, error) {
  	p.Lock()
  	defer p.Unlock()
  
  	xpk := p.fetch(id)
  	if xpk == nil {
  		if p.secring != nil {
  			return p.secring.Export(id, false)
  		}
  		return nil, fmt.Errorf("key not found")
  	}
  
  	return proto.Marshal(xpk)
  }
docs: // Export marshals a single key