online payments and credit cards: I have questions

[cellio]

As I make the rounds doing year-end donations, I'm reminded of two things that have long puzzled me:

1. Some web sites auto-detect the type of credit card based on the number. Apparently all credit-card numbers that begin with "4" are Visa. (I don't know if the reverse is true: do all Visa numbers start with 4?) Being me, I've cycled through the other nine digits and nothing else produces a match based on a single digit. What are the patterns for other providers? And are all these sites using some standard library for this, or are programmers really coding that by hand?

2. Years ago, a three-digit code ("CCV") was added to cards to mitigate fraud. On a physical credit card, this number is stamped rather than embossed, so those old-style manual credit-card gadgets that took an imprint of your card (on actual paper, with a carbon!) couldn't record it. Um, that's fine I guess, but online, that number isn't any more secure than the card number itself. And someone who steals your physical card has the number; it's not a password. Does that number have another purpose?

Comments

[(Anonymous)]

https://www.forbes.com/advisor/credit-cards/what-does-your-credit-card-number-mean/ and https://www.discover.com/credit-cards/card-smarts/what-is-a-credit-card-number/ (especially the latter) address the issue of the initial digits in the card number. If those are to be believed, then yes, Visa card numbers always and exclusively begin with 4, and MasterCard card numbers always and exclusively begin with 5.

/The Internet Dog :)

[cellio]

Thanks! Those both look very useful.