code: func (p *Secring) Set(pk *PrivateKey) error {
  	if !pk.Encrypted {
  		return fmt.Errorf("private key must be encrypted")
  	}
  
  	p.Lock()
  	defer p.Unlock()
  
  	p.insert(secKRToPB(pk))
  	return nil
  }
docs: // Set inserts a single key