Re: Generating Prepaid Card Numbers

Michael Fork wrote:

> We do not need the reseller's number, they purchase the cards ahead of
> time. As for you alternative pseudo RNG, where can I can find more
> info? A google on AES and CRT turned up nothing that jumped out at me
> as correct.
>
> Thanks.
>
> Michael
>

Reclaiming the 3 digits gives a check code and 2 extra digits. That
takes the number reuse time to a thousand years, i.e. it never happens
in the real world. That simplification can be used to strengthen your
security.

AES in CTR mode

The government standard.
http://csrc.nist.gov/CryptoToolkit/modes/workshop1/papers/lipmaa-ctr.pdf

Its use on communications links
http://rfc3686.x42.com/

An alternative pseudo random number generator is the encryption
algorithm AES in CTR mode. (Modified for 11 digits)

1. Initialise with a secret key value and iv.
2. Generate 128 bits.
3. Extract 48 bits and convert then to a 12 digit decimal number.
4. Keep last 11 digits to form your number.
5. Check number is unique, if it is then Output number and insert into
check list.
6. Add 1 to iv
7. Goto 2

Andrew Swallow
Received on Fri Dec 23 20:11:07 2005