code: func NewCrypto(ctx context.Context, id CryptoBackend) (Crypto, error) {
  	if be, found := cryptoRegistry[id]; found {
  		return be.New(ctx)
  	}
  	return nil, errors.Wrapf(ErrNotFound, "unknown backend: %d", id)
  }
docs: // NewCrypto instantiates a new crypto backend.