Credit Card Validation - Check Digits

This document outlines procedures and algorithms for Verifying the accuracy and validity of credit card numbers. Most credit card numbers are encoded with a "Check Digit". A check digit is a digit added to a number (either at the end or the beginning) that validates the authenticity of the number. A simple algorithm is applied to the other digits of the number which yields the check digit. By running the algorithm, and comparing the check digit you get from the algorithm with the check digit encoded with the credit card number, you can verify that you have correctly read all of the digits and that they make a valid combination.
Possible uses for this information:
When a user has keyed in a credit card number (or scanned it) and you want to validate it before sending it our for debit authorization.
When issuing cards, say an affinity card, you might want to add a check digit using the MOD 10 method.

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