![]() Of course, this would be clearer with a bit of code, and Listing 1 shows my IsCardNumberValid method. Finally, you add both totals together, and if the result is evenly divisible by 10, then the card number has passed the validation. Next, you do the same thing with the digits skipped in the first step, but this time you double the value of each digit and add the value of each digit in the result. To validate a credit card number, you start by adding the value of every other digit, starting from the right-most digit and working left. But, it does catch most typing errors, and reduces bandwidth usage by catching those errors before trying to actually process the credit card. In fact, it’s possible that the card number is mistyped in such a way that it just happens to pass verification. This verification does not tell you if funds are available on the account, and it certainly doesn’t tell whether or not the person submitting the order is committing credit card fraud. I recently had to write some code to process credit card orders, and thought I’d share a bit of my code.įortunately, credit card numbers are created in a way that allows for some basic verification. ![]() The following function takes a card number, including the check digit, as an array of integers and outputs true if the check digit is correct, false otherwise.When using ASP.NET to process online credit card orders, it is a good idea if you can perform some sort of validation on the credit card number before submitting it to your processor. Rather, the digits were marked in their permuted order on the body of the machine. The substitution digits, that is, the results of the double and reduce procedure, were not produced mechanically. The device took the mod 10 sum by mechanical means. The algorithm appeared in a United States Patent for a simple, hand-held, mechanical device for computing the checksum. Therefore, systems that pad to a specific number of digits (by converting 1234 to 0001234 for instance) can perform Luhn validation before or after the padding and achieve the same result. ![]() The Luhn mod N algorithm is an extension that supports non-numerical strings.īecause the algorithm operates on the digits in a right-to-left manner and zero digits affect the result only if they cause shift in position, zero-padding the beginning of a string of numbers does not affect the calculation. Other, more complex check-digit algorithms (such as the Verhoeff algorithm and the Damm algorithm) can detect more transcription errors. It will detect most of the possible twin errors (it will not detect 22 ↔ 55, 33 ↔ 66 or 44 ↔ 77). It will not, however, detect transposition of the two-digit sequence 09 to 90 (or vice versa). The Luhn algorithm will detect all single-digit errors, as well as almost all transpositions of adjacent digits.
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