code: func BzzPrivateKeyFromConfig(conf *adapters.NodeConfig) (*ecdsa.PrivateKey, error) {
  	// pad the seed key some arbitrary data as ecdsa.GenerateKey takes 40 bytes seed data
  	privKeyBuf := append(crypto.FromECDSA(conf.PrivateKey), []byte{0x62, 0x7a, 0x7a, 0x62, 0x7a, 0x7a, 0x62, 0x7a}...)
  	bzzPrivateKey, err := ecdsa.GenerateKey(crypto.S256(), bytes.NewReader(privKeyBuf))
  	if err != nil {
  		return nil, err
  	}
  	return bzzPrivateKey, nil
  }
docs: // derive a private key for swarm for the node key
  // returns the private key used to generate the bzz key