Advice on writing a basic encryption program?

Hello all,

Got a bit of the programming "bug" going on, and was just curious as to how difficult it would be to write an encryption/decryption program. I wasn't planning on anything too difficult; my main aim was focusing on - and learning to understand - the encryption process itself, rather than how it functions within larger applications.

Something basic like the user inputting a string, the string being converted into cipher text and output to file. Then, giving the user the option to reload the file and running a decryption algorithm, so that their original string can be viewed in tact.

Basically, my question is, do I go about devising the encryption/decryption algorithm myself, as I wouldn't have thought these methods would be divulged, because that'd sort of defeat the object of encryption.

Let me just clarify, I'm NOT asking for someone to do the algorithm for me, because I quite like the challenge of trying to implement it myself. However, I just wanted to hear the opinions of you guys, as my knowledge in this area is limited.

Thanks all.

There are quite a lot of post related to this thread, a quick search gave me this Encryption

ssharish

Actually, secret algorithms are regarded as a sign of "bad" crypto.
http://www.interhack.net/people/cmcu...e-oil-faq.html
All the good algorithms are well published and analysed, as are potential methods of attack.

You have to assume that the attacker has everything except your key.

If you're looking for an algorithm to implement, then a lot of people go with something simple like http://en.wikipedia.org/wiki/Caesar_cipher initially. Substituting different algorithms from then on is relatively trivial.

Coming up with a rock-solid algorithm along the lines of say RSA is not likely.