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Wyatt Says...

Moneybookers a.k.a. SkrillMoneybookers is quickly becoming a viable competitor to PayPal. And because of this our LimeLM customers have been asking for a completely automated payment form example similar to how our PayPal example works. That is, the customer enters the number of licenses they want, they click “Buy now”, they enter their info on the PayPal page, then they click “Order”, and a few seconds later the customer is magically sent their shiny new product key.

With PayPal this whole process is simple — just use the PayPal IPN (instant payment notification). That is, you specify an URL for PayPal to talk to once the order is complete. From there you can validate the order and take any action you like (e.g. sending product keys).

Moneybookers has a similar process except there are hardly any examples showing how to use it properly. And the example code that is on the web is riddled with very serious security vulnerabilities (SQL injections, failing to validate the order comes from Moneybookers, etc., etc.).

This article will show you how to use the Moneybookers equivalent to PayPal’s IPN. That is, you’ll be able to automatically generate product keys once a customer orders your software using Moneybookers. The code I post will be for both C# (ASP.NET) and PHP. If you would rather download a fully built payment form that lets you user switch between payment methods (credit card, bank transfer, PayPal, or Moneybookers), then you can signup for LimeLM and download the LimeLM Web API Pack. Here’s a screenshot of what payment form example looks like:

Payment example included in the LimeLM Web API Pack

Or, you can read on for the example that’s not specific to LimeLM.

Step 1. Signup for a Moneybookers test account

The first thing you need to do is get a test “merchant” account from Moneybookers. Unfortunately Moneybookers still doesn’t have a streamlined process for creating a test account, and their support staff is rather surly, so follow the instructions carefully:

  1. Sign up for a Moneybookers “Business account”. Do not use the same email you’ll be using for your real account.
  2. Sign up for a Moneybookers “Personal account”. Use a different email than the “Business account”. Do not use the same email you’ll be using for your real account.
  3. Contact Moneybookers and ask them to convert these 2 accounts to test accounts. It doesn’t need to be a long email. Just something simple like:

    We need you to turn 2 accounts to test accounts:

    “Buyer account”:
    Email: buyer-email@example.com
    Customer ID: 12456789

    “Merchant account”:
    Email: merchant-email@example.com
    Customer ID: 98765421

Step 2. Create a “secret word”

In your new merchant account you’ll need to create a “Secret Word” on the “Merchant tools” page:

Creating a Moneybookers secret word

Now that you’ve created your test Moneybookers accounts and set your secret word you’re ready to add the payment form to your website.

Step 3 (option 1). Use our pre-built payment form

If you’re using LimeLM you can use our pre-built payment form. Just configure a few settings, add the payment form to your site, and you’re ready to go. See the “Automate license generation with Skrill (a.k.a. Moneybookers)” article.

Step 3 (option 2). Create your own payment form

If you don’t want to use the pre-built payment example in the LimeLM API Pack, or you’re not using C#, VB.NET, or PHP, then you can still automate your orders with Moneybookers. The first step is to add the Moneybookers payment form to your website:

<form action="https://www.moneybookers.com/app/payment.pl" method="post">
  <input type="hidden" name="pay_to_email" value="merchant-email@example.com"/>
  <input type="hidden" name="status_url" value="http://example.com/verify.cgi"/> 
  <input type="hidden" name="language" value="EN"/>
  <input type="hidden" name="amount" value="Total amount (e.g. 39.60)"/>
  <input type="hidden" name="currency" value="Currency code (e.g. USD)"/>
  <input type="hidden" name="detail1_description" value="YourApp"/>
  <input type="hidden" name="detail1_text" value="License"/>
  <input type="submit" value="Pay!"/>
</form>

Change the “status_url” field to point to your script that will verify and generate the product keys and change the “pay_to_email” field to the test “merchant email” you created earlier. Then configure the price, currency code, and product name.

Optionally set your logo

You can customize the Moneybookers payment screen with your own logo. The logo must be hosted on a secure site — that is, the link must start with https:// not http://. Also, the logo must be at most 200px wide and 50px tall. If you have a logo that meets those requirements then add a “logo_url” field to your form. For example:

<input type="hidden" name="logo_url" value="https://example.com/logo.png"/>

This is an example showing what the wyDay logo looks like on the Moneybookers checkout page:

wyDay logo as seen on a Moneybookers checkout screen

Step 4. Verify the Moneybookers order

After a customer has completed their order through Moneybookers, Moneybookers will contact the script you provided in the “status_url” argument (e.g. “http://example.com/verify.cgi”). Moneybookers will POST the order information to your script and it’s up to you to verify that it’s a valid order and not just some hacker trying to get free product key from you.

Luckily Moneybookers gives the prescribed method for verifying orders in their gateway integration manual. Quoting from their manual:

A hidden text field called md5sig is included in the form submitted to the Merchant’s server. The value of this field is a 128 bit message digest, expressed as a string of thirty-two hexadecimal digits in UPPERCASE. The md5sig is constructed by performing an MD5 calculation on a string built up by concatenating the other fields returned to the status_url. Specifically the MD5 hash is a concatenation of the following fields:

  • merchant_id
  • transaction_id
  • the uppercase MD5 value of the ASCII equivalent of the secret word submitted in the “Merchant Tools” section of the Merchant’s online Moneybookers account.
  • mb_amount
  • mb_currency
  • status

PHP example code

In PHP this looks like (taken from paychecker.php):

// Validate the Moneybookers signature
$concatFields = $_POST['merchant_id']
    .$_POST['transaction_id']
    .strtoupper(md5('Paste your secret word here'))
    .$_POST['mb_amount']
    .$_POST['mb_currency']
    .$_POST['status'];

$MBEmail = 'merchant-email@example.com';

// Ensure the signature is valid, the status code == 2,
// and that the money is going to you
if (strtoupper(md5($concatFields)) == $_POST['md5sig']
    && $_POST['status'] == 2
    && $_POST['pay_to_email'] == $MBEmail)
{
    // Valid transaction.

    //TODO: generate the product keys and
    //      send them to your customer.
}
else
{
    // Invalid transaction. Bail out
    exit;
}

C# (ASP.NET) example code

In C# (for ASP.NET) this involves a bit more work. First create a simple helper function that creates the uppercase MD5 hash of a string:

static string StringToMD5(string str)
{
    MD5CryptoServiceProvider cryptHandler = new MD5CryptoServiceProvider();
    byte[] ba = cryptHandler.ComputeHash(Encoding.UTF8.GetBytes(str));

    StringBuilder hex = new StringBuilder(ba.Length * 2);

    foreach (byte b in ba)
        hex.AppendFormat("{0:X2}", b);

    return hex.ToString();
}

Then, the validation code will look something like this:

// Validate the Moneybookers signature
string concatFields = Request.Form["merchant_id"]
    + Request.Form["transaction_id"]
    + StringToMD5("Paste your secret word here")
    + Request.Form["mb_amount"]
    + Request.Form["mb_currency"]
    + Request.Form["status"];

string MBEmail = "merchant-email@example.com";

// Ensure the signature is valid, the status code == 2,
// and that the money is going to you
if (Request.Form["md5sig"] == StringToMD5(concatFields)
    && Request.Form["status"] == "2"
    && Request.Form["pay_to_email"] == MBEmail)
{
    // Valid transaction.

    //TODO: generate the product keys and
    //      send them to your customer.
}
else
{
    // Invalid transaction. Bail out
    return;
}

Step 5. Further verification, generating product keys, etc.

There’s one further step of verification I didn’t talk about: making sure the customer paid the correct amount. That is, verifying the “mb_amount” field is correct. For instance you don’t want to send a user a product key if they only pay 1 penny instead of the full amount. Also, you can further extend the payment form and the verification code to handle quantity. But this is a bit beyond the scope of the article. If you want to see that in action then download the example payment form included in the LimeLM Web API Pack.

Once you’ve verified the order you can use the limelm.pkey.generate web API function to generate product keys and email them to your customer.

Step 6. Test the payment form

Now that you have everything configured you’re ready to test your Moneybookers payment. Run through the complete payment process to see everything works how you expect it to work.

Step 7. Create a real Moneybookers account, change the setting

After you’ve finished testing your payment process you’re ready to sign up for a real Moneybookers “Business account” and change the “pay_to_email” field to the email you used to create this account.

Download full example code

We have a fully built payment page for PHP and ASP.NET (for C# and VB.NET) included in the LimeLM Web API Pack (get it on your API page). If you haven’t already signed up for LimeLM then sign up now. All plans have a 30-day free trial. Or, if you’re just putting your toes in the water, there’s even a free plan that has no time limit and doesn’t require a credit card.

In today’s article I’m going to talk about an interesting problem: detecting .NET assemblies. More than that, I’ll be talking about detecting some features of .NET assemblies and how you can expand and mold our code for your own uses. The code’s at the bottom of the article, it’s written in C# and licensed under the BSD license. Go get it.

I’ve seen this question pop up in a few different forms:

  • How do I detect .NET assemblies?
  • How can I detect the difference between .NET 2.0 and .NET 4.0 assemblies?
  • How can I detect the difference between x86, x64, and AnyCPU .NET assemblies?

And the list goes on and on. But this raises the question…

Why detect .NET assemblies?

We detect .NET assemblies because we respect humans’ time. Let me explain.

When wyUpdate (our open source updater) installs updates it can do a few things beyond simple patching, registry changing, and file copying. Namely it can:

  • NGEN assemblies
  • Install & update COM assemblies using RegAsm
  • Install & update assemblies in the GAC (Global Assembly Cache).

Which means wyUpdate needs to know whether the executable (or dll) is a .NET assembly, whether it’s strong signed, and what platform target it is (i.e. x86, x64, or Any CPU).

We could ask the user for every file, but that’s such a hassle. Who wants to waste time checking boxes for every exe and dll in their project? Rather than wasting the users’ time we quickly scan the .dll and .exe files for their details when the update is built inside wyBuild.

How not to do .NET detection

Do not use LoadLibrary(), or Assembly.Load() functions to load an assembly in memory to then parse it. This breaks when you have an x86 process trying to a load an x64 assembly (or vice versa).

How to detect .NET

Instead of using LoadLibrary (or one of its brethren) we’ll just treat the executables as dumb files. That is, just run a simple loop over the file and skip over the unneeded parts. You can check out the C# code posted at the bottom of this article, but you should be aware of 2 resources we used when designing the .NET detection algorithm:

The PECOFF spec gives you the general layout of .exe and .dll files, and the CLI Partition II gives .NET specific features that we detect. Namely, is the assembly strong signed, is it built for Any CPU or x86 alone, and what base version of the .NET framework is it built for (2.0 or 4.0).

Also, when you check out the code, notice how the code handles PE32 files versus how it handles PE32+ files. That is to say, 32-bit assemblies have a subtly different layout than 64-bit assemblies.

Tell me if you find this useful – how are you using it?

If you find this code useful, tell me how you’re using it in the comments.

Get the C# source

Download the AssemblyDetails C# source. It works with .NET 2.0, 3.0, 3.5, 4.0.

Example usage:

AssemblyDetails ad = AssemblyDetails.FromFile(filename);

// ad == null for non .NET assemblies
if (ad != null)
    Console.WriteLine(Path.GetFileName(filename) + ": " + ad.CPUVersion + ", " + ad.FrameworkVersion);
else
    Console.WriteLine(Path.GetFileName(filename) + ": Not a .NET 2.0+ executable.");

Update 7/3/2010: There was a slight bug in the first version. Re-download the code.

2 months ago we released wyBuild & wyUpdate v2.5. This release adds a free automatic updater control for C# & VB.NET apps. And because we wanted to keep things simple we left the wyUpdate.exe to do all the hard work (checking, download, installing) in the background while the AutomaticUpdater control is visible on your app’s main form.

We wanted the AutomaticUpdater to be able to control the update steps, view progress, and cancel the updating. But we also wanted to keep all the updating logic in the wyUpdate.exe. For this to be successful we needed a way for the AutomaticUpdater control to talk to wyUpdate.exe while it’s running.

The Answer: Inter-process communication (IPC)

Inter-Process communication is a fancy computer science way of saying “processes that can talk to each other”. Google Chrome uses IPC to communicate between tabs of the browser & plugins. It’s a simple way to keep parts of your program isolated from crashes.

For instance, if a tab of Google Chrome crashes only that single tab is killed. The rest of your tabs will continue to function normally.

Lots of bad ways to do IPC

Now that you know what inter-process communication is, let me tell you the worst ways to do it.

  • Shared memory: Difficult to set up & difficult to manage.
  • Shared files / registry: Very slow due to the writing & reading to/from disk. Difficult to manage.
  • SendMessage / PostMessage: Locks up the UI thread while the message is processed. Messages are limited to integer values. Can’t communicate from a non-admin process to an admin process. Assumes that your processes have a window.

Named Pipes

Inter process communication using named pipes is what Google Chrome uses and what we use for wyUpdate and the AutomaticUpdater control. Let me teach you about named pipes.

“Like Mario’s pipes?”

Exactly like Mario’s pipes. Except, instead of jumping Mario through the pipe, you push data through the pipe:

What do you put in the pipe?

You can transfer any data between your processes. So what data should your transfer? The answer is “it depends”. The rule of thumb is to keep it short, and keep it simple. Here’s what we do with the named pipe between wyUpdate and the AutomaticUpdater control sitting on your application:

  • Command codes: The AutomaticUpdater can command wyUpdate to check for updates, download the updates, extract the update, and install the update, or cancel any current progress.
  • Responses: wyUpdate can tell the AutomaticUpdater if there’s an update available, what changes there are in the update, and the progress of the current step (e.g. downloading).

With this simple setup the AutomaticUpdater control that’s on your application is completely isolated from wyUpdate.

Get the C# source

Download the named pipes C# source. It works with .NET 2.0, 3.0, 3.5 on Windows 2000 – Windows 7.

There are two files that do all the work: PipeServer.cs and PipeClient.cs. We use the PipeServer.cs file inside wyUpdate, and we use the PipeClient.cs file inside the AutomaticUpdater control.

Also included in the zip file is a simple messaging program to demonstrate communication between two separate processes:

Tell me what you think in the comments. I want to hear from you.