code: func (whisper *Whisper) AddKeyPair(key *ecdsa.PrivateKey) (string, error) {
  	id, err := GenerateRandomID()
  	if err != nil {
  		return "", fmt.Errorf("failed to generate ID: %s", err)
  	}
  
  	whisper.keyMu.Lock()
  	whisper.privateKeys[id] = key
  	whisper.keyMu.Unlock()
  
  	return id, nil
  }
docs: // AddKeyPair imports a asymmetric private key and returns it identifier.