How to generate a verification code/number?

Question

I\'m working on an application where users have to make a call and type a verification number with the keypad of their phone.

I would like to be able to detect if th

Answer 1

Assuming you already know how to detect which key the user hit, this should be doable reasonably easily. In the security world, there is the notion of a "one time" password. This is sometimes referred to as a "disposable password." Normally these are restricted to the (easily typable) ASCII values. So, [a-zA-z0-9] and a bunch of easily typable symbols. like comma, period, semi colon, and parenthesis. In your case, though, you'd probably want to limit the range to [0-9] and possibly include * and #.

I am unable to explain all the technical details of how these one-time codes are generated (or work) adequately. There is some intermediate math behind it, which I'd butcher without first reviewing it myself. Suffice it to say that you use an algorithm to generate a stream of one time passwords. No matter how mnay previous codes you know, the subsequent one should be impossibel to guess! In your case, you'll simply use each password on the list as the user's random code.

Rather than fail at explaining the details of the implementation myself, I'll direct you to a 9 page article where you can read up on it youself: https://www.grc.com/ppp.htm