code: func (api *PublicWhisperAPI) GetPublicKey(ctx context.Context, id string) (hexutil.Bytes, error) {
  	key, err := api.w.GetPrivateKey(id)
  	if err != nil {
  		return hexutil.Bytes{}, err
  	}
  	return crypto.FromECDSAPub(&key.PublicKey), nil
  }
docs: // GetPublicKey returns the public key associated with the given key. The key is the hex
  // encoded representation of a key in the form specified in section 4.3.6 of ANSI X9.62.