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Credit Card Validation

"Although online payment options such as PayPal have become extremely popular in the last couple of years, the majority of online stores still use some sort of merchant system to accept credit card payments from their web sites. Before actually encrypting your customer's credit card numbers to a database or forwarding them to a merchant server, it's a good idea to implement your own credit card validation routine."

Introduction

Although online payment options such as PayPal have become extremely popular in the last couple of years, the majority of online stores still use some sort of merchant system to accept credit card payments from their web sites. Before actually encrypting your customer's credit card numbers to a database or forwarding them to a merchant server, it's a good idea to implement your own credit card validation routine.

In this article we're going to work through developing a PHP class that stores the details of a credit card and validates its number using the Mod 10 algorithm. To implement the class that we will create in this article, you should have access to an Apache web server running PHP 4.1.0 or later.

Credit card validation

What does we actually mean when we say "validate a credit card number"? Quite simply it means that we run a credit cards number through a special algorithm known as the Mod 10 algorithm.

This algorithm processes some simple numerical data validation routines against the number and the result of this algorithm can be used to determine whether or not a credit card number is valid. There are several different types of credit cards that one can use to make a purchase, however they can all be validated using the Mod 10 algorithm.

As well as passing the Mod 10 algorithm, a credit card number must also pass several different formatting rules. A list of these rules for each of the six most popular credit cards is shown below:

-Mastercard: Must have a prefix of 51 to 55, and must be 16 digits in length.
-Visa: Must have a prefix of 4, and must be either 13 or 16 digits in length.
-American Express: Must have a prefix of 34 or 37, and must be 15 digits in length.
-Diners Club: Must have a prefix of 300 to 305, 36, or 38, and must be 14 digits in length.
-Discover: Must have a prefix of 6011, and must be 16 digits in length.
-JCB: Must have a prefix of 3, 1800, or 2131, and must be either 15 or 16 digits in length.

As mentioned earlier, in this article we will be creating a PHP class that will hold the details of a credit card number and expose a function indicating whether or not the number of that credit card is valid (i.e. whether it passed the Mod 10 algorithm or not). Before we create that class however, let's look at how the Mod 10 algorithm works.

The Mod 10 algorithm
There are three steps that the Mod 10 algorithm takes to determine whether or not a credit card number is valid. We will use the valid credit card number 378282246310005 to demonstrate these steps:

Step One
The number is reversed and the value of every second digit is doubled, starting with the digit in second place:

378282246310005

... becomes ...

500013642282873

and the value of every second digit is doubled:

5 0 0 0 1 3 6 4 2 2 8 2 8 7 3
x2 x2 x2 x2 x2 x2 x2
-------------------------------------------
0 0 6 8 4 4 14

Step Two
The values of the numbers that resulted from multiplying every second digit by two are added together (i.e. in our example above, multiplying the 7 by two resulted in 14, which is 1 + 4 = 5). The result of these additions is added to the value of every digit that was not multiplied (i.e. the first digit, the third, the fifth, etc):

5 + (0) + 0 + (0) + 1 + (6) + 6 + (8) + 2 + (4) + 8 + (4) + 8 + (1 + 4) + 3

= 60

Step Three
When a modulus operation is applied to the result of step two, the remainder must equal 0 in order for the number to pass the Mod 10 algorithm. The modulus operator simply returns the remainder of a division, for example:

10 MOD 5 = 0 (5 goes into 10 two times and has a remainder of 0)
20 MOD 6 = 2 (6 goes into 20 three times and has a remainder of 2)
43 MOD 4 = 3 (4 goes into 43 ten times and has a remainder of 3)

So for our test credit card number 378282246310005, we apply a modulus of 10 to the result from step two, like this:

60 MOD 10 = 0

The modulus operation returns 0, indicating that the credit card number is valid.

Now that we understand the Mod 10 algorithm, it's really quite easy to create our own version to validate credit card numbers with PHP. Let's create our credit card class now.

Creating the CCreditCard class

Let's now create a PHP class that we can use to store and validate the details of a credit card. Our class will be able to hold the cardholders name, the card type (mastercard, visa, etc), the card number, and the expiry month and date.

Create a new PHP file called class.creditcard.php. As we walk through the following two pages, copy-paste each piece of code shown to the file and save it.

We start of by defining several card type constants. These values will be used to represent the type of card that our class will be validating:

And that's all there is to our CCreditCard class! Let's now look at a simple validation example using HTML forms, PHP, and an instance of our CCreditCard class.

Using our CCreditCard class

Create a new file called testcc.php and save it in the same directory as the class.creditcard.php file. Enter the following code into testcc.php:

Validate Credit Card

Cardholders name:
Card number:
Card type:
mastercard
Visa
Amex
Diners
Discover
JCB

Expiry Date:

Validation Results
Name:
Number:
Type:
Expires:

Run the script in your browser.

Conclusion

In this article we've seen how we can take advantage of PHP's object orientated nature (most notably classes) to create a credit card storage and validation class. We went through the components of this class in detail, and we finished off by creating a test script in which we instantiated our CCreditCard class and validated a sample card number.

If you're thinking of setting up an eCommerce site which will process/store visitors credit card details, then you should take the class we've just made and customize it to suit your needs. You might want to add other functions to it to compare CCreditCard objects, format the cards details into an XML string, encrypt the cards details to a database, or even process the payment in real time.

/This article was provided by ThePHPGuy.com -- home of the never-ending collection of articles for Apache, PHP and MySQL. Check them out at http://www.thephpguy.com