4 ms·
> if you need more entropy then add another digit. That would break so much as most of the message formats and batch files use fixed width fields. It's probabl
by leejo 10y ago
> if you need more entropy then add another digit.
That would break so much as most of the message formats and batch files use fixed width fields. It's probably the same for the databases underneath. Changing to alphanumerics sounds nice but the check digit algorithm would have to change from Luhn to Luhn mod n. More breaking changes.
Banking systems are one of the ultimate forms of legacy, which is why most of the security additions have been bolted on. Just look at 3D secure - they added an entire subsection to the message format and it was still just another single factor auth method that nobody wanted and everybody hated.
- digler999 10y ago> but the check digit algorithm would have to change or just get rid of it. It was a relic from 20+ years ago when networks and computers were 1/100th the speed they are today. Let them enter invalid numbers. Let the server return an error (as it already does)
- rlucas 10y agoSimilarly, once we did away with legacy electromechanical phone switches, the (phone area code) NANPA started allowing area codes with non-[0,1] middle digits. The big form of 10-digit numbers was retained and extended by relaxing a legacy constraint.
- avar 10y agoThe check digit gets used today by e.g. JavaScript in input forms to indicate a typo in the card number.