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inveni0
04-12-2007, 08:55 PM
I'm working on something for a client. They need to store credit card numbers in their database but will also need to retrieve these numbers. They do not want to store the numbers with no encryption. So, I'm working on some encryption code. If any of you enjoy a challenging puzzle, please give this a go!


The following is the encrypted version of a number:
CDB433H333G3CCGF

Some facts to help you solve it:
1) The card number is 16 digits in length.
2) The number begins with a 9.
3) The number has been encrypted using simple substitution.

Successfully solve this, and I'll be happy to award you with free web site hosting for one year (on my servers, so no ads or anything silly) if you should be in need.

Thanks for your help!
Nippur
05-12-2007, 06:14 AM
Interesting, I'll try it...after I get home from work and get some sleep.
neolith
05-12-2007, 12:52 PM
The number is...1.Am i close?
inveni0
05-12-2007, 02:11 PM
Interesting, I'll try it...after I get home from work and get some sleep.

Excellent. Thanks, man.

The number is...1.Am i close?

Dang. You're good. ;)
inveni0
05-12-2007, 03:46 PM
My encryption process has changed a bit. I've altered the above number accordingly.
Nippur
05-12-2007, 04:56 PM
And is it still "simple substitution" ? :)
inveni0
05-12-2007, 05:29 PM
Yes. :)
Freespace-3DT
05-12-2007, 07:04 PM
Is it 9084 3343 3333 9932 ?
inveni0
05-12-2007, 08:13 PM
Is it 9084 3343 3333 9932 ?

No. But that's an amazing estimate, Freespace. Maybe too close for comfort. You aren't 'on the edge' of being right, but your patterns are very close.
Freespace-3DT
05-12-2007, 09:11 PM
How about 9804 3343 3353 9956 ?

Another hint, are the numbers in the code you've given us final? I mean, does 4 remain 4, for example?
inveni0
05-12-2007, 09:33 PM
Freespace, if I hadn't changed my code a bit, you would be close enough to run the number you've come up with through a computer program that would check different arrangements of the number against the LUHN formula until it found a match.

I feel confident, however, that my most recent addition makes the number impossible to decode without significant computer power and hours and hours of processing time. And with that amount of power, you'd might as well hack MasterCard.

Thanks for your help, man. You're welcome to keep trying, too (even though you already have free hosting from me :dunno:)

EDIT: and no, 4 does not remain 4
Freespace-3DT
05-12-2007, 09:34 PM
It's just that I like a logic challenge. :) Nice encryption, but it's as far as I go with my 1337 skillz of decryption.
inveni0
05-12-2007, 09:44 PM
Yeah. I don't think it can be done with a normal brain. Someone would have to write a program specifically for deciphering this (especially since it doesn't use a common key of any kind), and I just think there are easier ways to get lists of credit card numbers. This is, in total, 7 stage encryption.

What led me to believe that it could be decrypted is the fact that it's designed to be decrypted--meaning it's possible. But as I tried to decrypt the number, I couldn't even decide where I'd want to start. Especially since I know what my typical approach would be (similar to yours) and that it would indeed give me a final solution that, while close, was a waste of effort, equivalent to having never tried to decrypt it.

I think my clients will be satisfied with this.