Validating Credit Card Numbers

Lately, I’ve been working on an e–commerce website and discovered a handy algorithm for validating card numbers. The Luhn algorithm (also known as mod 10) is a checksum formula and is used to protect against accidental errors rather than malicious attacks.

The algorithm is particularly useful for checking to see if the card number ‘looks’ right before sending it off to the payment provider for processing. This reduces the amount of rejected card payments, which is always a good thing. 🙂

More details of how the algorithm works can be found on Wikipedia and my annotated PHP implementation can be found below.