4 ms·

Interesting post, and I'm not surprised to see a diversity of opinion on the design. Question: does anyone still use the CRC validity check for client- or serve

• incarnate 11y ago
  You're talking about a Luhn check? I still see it as common practise, particularly on the client side. Interesting that the article didn't mention it as a validation point (only card number length), but testing their demo it does do the check.
  • markbnj 11y ago
    Yes, exactly. I had forgotten the name, and I also found it interesting that it wasn't mentioned.
• mynameisvlad 11y ago
  Does anyone not? It's a dead stupid simple way to check that the card number entered could possibly be valid, so you can let your users know earlier in the process (during client side validation) that there may be an issue.
  • bediger4000 11y ago
    Yes. Luhn checksum detects adjacent digit transposition errors, which I'd tend to believe are the most common, and it will detect a single wrong digit, which might be most or second most common. It's a simple check, although all the example code I've seen is grotesque. The lesson here is that when you're dealing with those pirates that do the "Rachel from Account Services" scam cold calling, transpose two digits seperated by another digit. Don't monkey with the first 7 digits or the final digit. You can get those idiots to go all the way through verifying your (incorrect) card number, as the BIN/IIN is correct and Luhn check passes. Waste some time on double checking your card number before spewing vitriol and profanity on them.