playfair-rs - Playfair Cipher in Rust.

Originally was an assignment for my CS 303: Databases and Information Security class, I wanted to take some more time and implement it again. This is my solution to implementing the Playfair Cipher in Rust.

Design choices

Some implementations omit the letter 'q' in encryption/decryption, some omit 'j', and some equate 'i' to 'j'. For my implementation, I went with 'i' = 'j', since that is what the Wikipedia article's example followed, and a random online playfair cipher website used by default. This allowed for easy verification of my implementation.

I also used a Makefile to enforce strict commenting of all my functions to ensure I knew what was going on at that line and function. As well thanks to the awesome Rust ecosystem, it enables generation of documentation with just a single make command. That documentation can be found in the ./target/doc/playfair_rs/ directory, following execution of the make command.

I also used testing extensively, for each part from keyword generation, matrix computation, character location, to full integration testing. Combining this with assertions in the code, I have a pretty good idea that my code is correct.

Examples

You can see an example in main.rs, or here is a simple shown implementation:

Encryption steps:

use playfair::{Cipher, Playfair};

// Example from https://en.wikipedia.org/wiki/Playfair_cipher.
fn main() {
    let pf = Playfair::new("playfair example");
    let out = pf.encrypt("Hide the gold in the tree stump.");

    // out = bmodzbxdnabekudmuixmmouvif
}

Decryption steps:

use playfair::{Cipher, Playfair};

// Example from https://en.wikipedia.org/wiki/Playfair_cipher.
fn main() {
    let pf = Playfair::new("playfair example");
    let out = pf.decrypt("bmodzbxdnabekudmuixmmouvif");

    // out = hidethegoldinthetrexestump
    // NOTE: the extra 'x' here ^ is expected since it was inserted during the encryption process.
    // Read more about the Playfair cipher to understand why.
}