Why didn't you answer any of his other questions? It's extremely hard to answer a security question without having some background knowledge. In this case, it's very important to know:

1) What is this number? If it's a password, we can simply hash it instead of encrypting it. That would eliminate the key management problem.

2) From what you are trying to protect this number? A casual glance? Something you don't want eavesdropped during transmission? Something stored locally and the user can be prompted for a key? Something stored locally, but there is no user interaction?

Your significant lack of effort is displeasing.

flamel

You still have not explained what you want to do with this hidden number and how it is to be got back again. Who are you hiding this number from ? The legitimate user of your code (impossible without a trusted hardware platform) or evil hackers (encrypt number with password only known to user, implement crypto correctly (v.hard) ).

It does look like you want to re-implement some crypto from scratch in your code. This is a bad idea especialy as perl already has good crypto modules. Please see the Schneier book Fletch refers too and if you insist on going ahead read Applied Cryptography by the same author too.

If you do decide to implement your own then go and look at the source code for some of the crypto modules on CPAN although it does sound rather silly to make an error prone re-implementation of something you can pull down for free.

Cheers,
R.