code: func (ks *Keystore) StoreTrustedKeyPrefix(prefix string, r io.Reader) (string, error) {
  	acidentifier, err := types.NewACIdentifier(prefix)
  	if err != nil {
  		return "", err
  	}
  	return storeTrustedKey(path.Join(ks.LocalPrefixPath, acidentifier.String()), r)
  }
docs: // StoreTrustedKeyPrefix stores the contents of public key r as a prefix trusted key.