code: func (ks *Keystore) MaskTrustedKeySystemPrefix(prefix, fingerprint string) (string, error) {
  	acidentifier, err := types.NewACIdentifier(prefix)
  	if err != nil {
  		return "", err
  	}
  	dst := path.Join(ks.LocalPrefixPath, acidentifier.String(), fingerprint)
  	if err := ioutil.WriteFile(dst, []byte(""), 0644); err != nil {
  		return "", err
  	}
  	if err := os.Chmod(dst, 0644); err != nil {
  		return "", err
  	}
  	return dst, nil
  }
docs: // MaskTrustedKeySystemPrefix masks the system prefix trusted key identified by fingerprint.