hedzer/urchin

Urchin is a symmetric n-bit block cipher with extreme disdain for constants.

Urchin

Urchin is a symmetric n-bit block cipher with extreme disdain for constants.

Disclaimer

This project is not intended for production use. It is a for-fun library built to add to my experiences.

Usage

Simply build and import the library into your project. From there it's as easy as using the provided API. Here is an example:

using Urchin;
Cipher cipher = new Cipher 
{
	Key = key,  // your key
	IV = iv    // your IV (basically a salt)
};
// encrypts a string
byte[] encrypted = cipher.Encrypt("hello");
// decrypts a byte array
byte[] decrypted = cipher.Decrypt(encrypted);
// convert back to string
string original = Encoding.ASCII.GetString(decrypted);
// displays "hello"
Console.WriteLine(original);

What's it for?

It's primarily built for encrypting small snippets of text. A messaging app would be an ideal use case.

How does it behave?

Urchin is slow by design (yeah... sure). It's meant to be difficult to brute force. It has no set number of rounds, block, or words sizes; everything is pseudo-randomly selected. Pseudo-random entropy is created by using existing hash algorithms and hashing recursively. The set of hashes used is shuffled after each round.

During each round a block is broken down into words of a pseudo-randomly selected size and passed through an algorithm that transposes or modifies the bits in that word. The algorithms that transform & transpose are also in a pseudo-random order, and are continuously shuffled.

Regrets

I gave myself a week to do this project, which had originally been postponed for more than a year. I would have liked to have built a Feistel style cipher a la Bruce Schneier's Blowfish. Perhaps a 2.0 version could be worked out in the future.