crypto computer programming

[daverules]

I am currently in a beginning c++ class. We have to come up with our own program to write for the end of the semester.

I want to write a crypto program. You'll have to input text, I'll encrypt it. It'll take the ciphertext and output it to a file or something.

The thing I need is a good, relatively strong, cryptography method that can be done by hand. I then want to write a computer program that will automate it.

I am thinking about using the Solitaire/Pontifex method described in Neal Stephensen's Cryptonomicon and here . Are there any other good ones out there?

Thanks!

 

[CSoup]

How about RSA? I remember having to do it by hand for an abstract algebra class.

 

[Beau]

I wrote a cool little complex progressive character replacement program in VB. I haven't had anyone try to crack it yet, but it seams pretty strong

 

[LiquidCyanide]

Look up the Diffe-Helman algorithm it is a rather simple algorithm which uses the properties of exponents to cancel out unknowns with a randomly generated number and a known number transferred between the two parties. I believe it is implemented in Blowfish encryption.

 

[Armitage]

You could do a book code, or one-time pad system if you want to keep it simple.

 

[Carceri]

If you want to implement a really simple algorithm do the RC4 stream cipher. It's very easy to implement and also secure giving that you avoid the few pitfalls there are (repeat the state array mixing routine approx 20 times instead of one is probably the most important one). If this is too simple try implementing the IDEA or RC6 algorithm. IDEA is the conventional algorithm used in PGP and RC6 is an advanced version of the RC5 encryption algorithm. Both are secure and easy to implement. RC6 is probably the easiest.

If you want to extend it, you could write routines so that it could encrypt data in ECB, CBC and CFB modes.

I don't suggest trying to implement a public key system (RSA, DH, El-Gamal, etc...) since they require much more code to work.

 

[Carceri]

<< Look up the Diffe-Helman algorithm it is a rather simple algorithm which uses the properties of exponents to cancel out unknowns with a randomly generated number and a known number transferred between the two parties. I believe it is implemented in Blowfish encryption. >>


You are describing DH Key Exchange or DH Key Predistribution. This only exchanges a session key, but can't do any encryption. I think he wants to implement an encryption algorithm.

Blowfish has nothing to do with DH Key Exchange.