code: func getEnvelopePrefixTransformer(config *apiserverconfig.KMSConfiguration, envelopeService envelope.Service, prefix string) (value.PrefixTransformer, error) {
  	envelopeTransformer, err := envelope.NewEnvelopeTransformer(envelopeService, int(config.CacheSize), aestransformer.NewCBCTransformer)
  	if err != nil {
  		return value.PrefixTransformer{}, err
  	}
  	return value.PrefixTransformer{
  		Transformer: envelopeTransformer,
  		Prefix:      []byte(prefix + config.Name + ":"),
  	}, nil
  }
docs: // getEnvelopePrefixTransformer returns a prefix transformer from the provided config.
  // envelopeService is used as the root of trust.