code: @Deprecated
      /*package*/ static SecretKey getLegacyKey() throws GeneralSecurityException {
          String secret = Secret.SECRET;
          if(secret==null)    return Jenkins.getInstance().getSecretKeyAsAES128();
          return Util.toAes128Key(secret);
      }
docs: Turns {@link Jenkins#getSecretKey()} into an AES key.
  
  @deprecated
  This is no longer the key we use to encrypt new information, but we still need this
  to be able to decrypt what's already persisted.