Asking a smart question

/by apr/

Among the many helpful jPOS developers in our community, @marklsalter stands out for his professional, accurate, and detailed answers, but he has his standards when it comes to how you ask questions. You need to ask a smart question. jPOS has Mark (and Victor, and Andy, and Dave, and Matias, and Chhil, and Barzi, and, and, and), but if you go to any other open source community asking for free advice, you’ll find another Mark, or worst than that, you’ll find no Mark and your question will just get ignored and you won’t even know why.

This is what you should expect as a response if you don’t do your homework and ask a smart question (from a recent reply in jpos-users, in this case, related to a vague question about to the Transaction Manager - could have been anything else).

Please always start by asking a smart question.

Please read this now :-

Yes, the whole things, go on, treat yourself, it will take 5-10 minutes and save us both hours going forward.

Preparing to ask a smart question should cause you to read the available documentation, to understand it and enable you to make sure you include all the relevant details needed for another remote person to help you, but should also make sure you have understood the documentation and how it applies to your need.

I can honestly say that on this opening post that I could see that it was going to be another thread that would drag on - without you …

  1. Apparently making any effort to understand what you have done incorrectly or “misunderstood”.
  2. Trying first to understand how and why your set-up is broken
  3. Referring to the documentation on the life cycle of the TransactionManager and it’s given participants - which perhaps surprisingly, works perfectly when users follow the few simple rules and grasp what it does for you.

By the way, I understand that a TM configuration might not be obvious straight away, but often the best things are worth the effort. I still refer to the documentation again and again (and again).

I will include some comment below to, in the hope that you read it and take the time next time to ask a smart question.

Remember as you read through that I am not taking the piss out of you, but trying to highlight why this is a terrible opening question and how you can (hopefully) help yourself next time.

jPOS-EE Crypto Service

In many jPOS systems, we secure sensitive data using ANS X9.24 DUKPT as described in the Encrypting sensitive data post. The approach served us well, but now we believe we have a better one, using PKI and AES-256.

The cryptoservice module uses AES-256 to encrypt sensitive data, such as primary account numbers and protects the encryption key using PGP.

At start-up time, and at regular intervals, the crypto service generates a new AES-256 key, encrypts it using PGP using one or more recipient ids, and stores the resulting encrypted message in the sysconfig table, using the “key.” prefix, and a unique key UUID, i.e.:

id: key.f55fe6ec-ed9e-47a1-a0fe-c63dcbf128cb
Version: BCPG v1.56



The key is used to encrypt subsequent data for a given period of time (defaults to one day) until a new key is automatically generated.

Here is a sample usage:

private void encryptCardData (TLCapture tl, Card card)      <1>
   throws Exception {
     Map<String,String> m = new HashMap<>();
     m.put ("P", card.getPan());
     m.put ("E", card.getExp());
     SecureData sd = getCryptoService().aesEncrypt(         <2>
     tl.setKid(sd.getId());                                 <3>
     tl.setSecureData(sd.getEncoded());                     <4>
  • <1> TLCapture in this example is a general purpose capture table.
  • <2> getCryptoService() just locates the CryptoService using the NameRegistrar
  • <3> kid stands for Key ID, we store the key UUID here
  • <4> secureData is a general purpose blob

The crypto service can be configured using a QBean descriptor like this:

<crypto-service class='org.jpos.crypto.CryptoService' logger='Q2'>
    <property name="custodian" value='' />               <1>
    <property name="pubkeyring" value='cfg/' />            <2>
    <property name="privkeyring" value='cfg/keyring.priv' />          <3>
    <property name="lazy" value="false" />                            <4>
    <property name="keylength" value="256" />                         <5>
    <property name="duration" value="86400000" />                     <6>
  • <1> custodian PGP id, there can be many custodian entries.
  • <2> path to the public keyring.
  • <3> path to the password-protected private keyring.
  • <4> if lazy=true, a key is generated the first time we call aesEncrypt, otherwise, a new one is created at service start.
  • <5> key length defaults to 256. Can be reduced if AES-256 is not supported by the JVM due to export restrictions.
  • <6> key duration

This allows jPOS nodes to encrypt data securely without storing the encryption key to disk.

NOTE: The transient encryption key is still in memory, so core dumps and swap should be disabled at the operating system level. This approach is still more secure than obfuscating encryption keys.

Decryption – that can of course run in a different node, at a different time – requires access to the private keyring, with its optional password. Said password can be entered manually, obtained from a remote service or HSM, etc. and it’s a two step process.

First the key has to be loaded into memory, using the loadKey method. Once the key is loaded, the aesDecrypt can be called.

These are the method’s signatures:

public void loadKey (String jobId, String keyId, char[] password) throws Exception;
public byte[] aesDecrypt (String jobId, String keyId, byte[] encoded) throws Exception;

Here keyId, password, and encoded cryptogram don’t require too much explanation, but jobId does and here is the rationale. We could have a one-shot aesDecrypt method accepting the private key password, but decrypting the AES-256 key using PGP is an expensive operation. In situations where you have extract a daily file, probably encrypted by just a handful keys, you don’t want to decrypt the key on every aesDecrypt call. We don’t want to expose the key to the caller either, so the CryptoService keeps it in a private field. In order to do that, loadKey caches the key (until it’s unloaded), so it’s cheap to call loadKey followed by aesDecrypt, after the first call where the key is actually decrypted, subsequent calls will be pretty fast.

In order to protect different clients from accessing keys loaded by other ones, we use a jobId that can be something as simple as a UUID or any nonce, only known to the caller. That jobId can then be used to unload those keys, using the unloadKey and unloadAll methods:

public boolean unloadKey (String jobId, String keyId);
public void unloadAll(String jobId);

There’s also a no-args unloadAll() that unloads all keys, and should be used with care.

NOTE: In order to simplify development and testing, and eventually to troubleshoot problems, we’ve also created a couple of CLI commands: aesencrypt and aesdecrypt.

TIP: If you’re accessing the CLI using the command line q2 --cli, remember that the default deployDir is deploy-cli instead of deploy. You need a copy (or symlink) of 25_cryptoservice.xml in that directory. If you ssh to a running Q2 to reach the CLI, then you can ignore this tip.

For up-to-date information about this CryptoService module, please see the jPOS-EE guide.


There’s a new handy org.jpos.transaction.TxnId class in the jPOS-EE txn module that can be used to generate transaction ids in multi-node systems.

The id is composed of:

  • 1-digit century
  • 2-digits year
  • 3-digits day of year
  • 5-digits second of day
  • 3-digits node id
  • 5-digits transaction id

A typical ID long value would look like this: 173000702600000001, and the toString() method would show as 017-300-07026-000-00001 and the toRrn() method would return 1bbfmplq9la9.

TxnId also has a handy toRrn() method that can be used to create (and parse) 12-characters strings suitable to be used as retrieval reference numbers.

TxnId can be used instead of UUIDs. It puts less pressure in the database index and provides chronological order.

NOTE: The last two groups, node-id and transaction-id are supposed to be unique. transaction-id is easy to get from the transaction manager and node-id is a tricky one, user has to ensure each node has a unique node-id to avoid collisions.

Sample usage:

TxnId txnId = TxnId.create(, 0, id);

jPOS 2.1.0 has been released

jPOS 2.1.0 has been released, new development version is now 2.1.1-SNAPSHOT

Please see the ChangeLog.

Remember we are using Semantic Versioning so the change from 2.0.10 to 2.1.0 means a full rebuild has to be done in your applications. Some of the most notable changes are:

  • TransactionContext is now backed by a Map<String,Object> instead of the old Map<Object,Object> so that needs review
  • Some methods that used to throw ISOException are not throwing it anymore

Other than those two minor changes, jPOS 2.1.0 has a large number of improvements, including TransactionManager metrics, new org.jpos.rc package, bug fixes and improved TransactionManager capacity.

jPOS-EE 2.2.4 has been released as well, new development versions are jPOS 2.1.0-SNAPSHOT and jPOS-EE 2.2.5-SNAPSHOT.

See Resources Page for details.

Tutorial - Writing a gateway the jPOS way

I get to see dozens of third party jPOS gateway implementations just using 5% of jPOS capabilities.

People download jPOS just to use the ISO-8583 packing/unpacking and sometimes they don’t even get to use the channels, multiplexers, servers, transaction manager. I see developers trying to stay away from Q2 probably because they don’t know it, but it’s quite simple to use.

So I wrote a little tutorial, that walks you through the process of installing jPOS and writing a production grade gateway capable of processing thousands of transactions per second.

The tutorial has two parts, first you get it running (takes about 5 minutes), then the second part explains why that very simple configuration works.

The second part has plenty of links to the jPOS programmer’s guide documentation (freely available), while it’s just a couple pages, understanding it and following the links may take some more time and may raise some questions that we’ll be happy to answer.

Investor's Dilemma : How do I Handle Unlicensed Copies of AGPL Software in a Portfolio Company

Every once in a while we receive a request from an investor or private equity firm who, in the process of conducting due-diligence on an existing or established potential portfolio company, encounters an unlicensed copy of jPOS. Often the company has released a commercial product which incorporates this unlicensed software. Investors want to know, how should we proceed and what are the responsibilities of the company vis-à-vis the license and source code?

The easiest and first answer is of course, the company should purchase a license and not rely on pirated software to conduct their business. The more subtle question is what does it imply when a start-up is willing to pirate software which is intended to be reasonably priced and positioned to benefit the authors and the overall Fintech software community as a whole?

Isn’t it risky to partner with a company that disregards good business practices, either because of bad faith or negligence?

If it were me, I’d invest somewhere else!