📁 Best Worst Compression

So,,, I think I may have just made the best worst compression system ever. I’ve had this idea for a while and finally decided to make this mess a reality. It compresses any file size to around 40 bytes, the catch is the decompression time. For my 4 byte test file, Hi\r\n it took like thirty minutes to decompress.

🦄 How it works

So, let’s see how this very ingenious system works!

Compression

For compression of a file, we take the hash of the file and the number of bytes in it. This data is then written to a new file. Yeah, that’s all. At the very least, it’s fast. I think you can see where this is going…

Here is the code I made for compression:

fn compress<T>(file: T)
where
    T: AsRef<Path>,
{
    let inp = fs::read(&file).unwrap();
    let size = inp.len();

    let mut hasher = Sha256::new();
    hasher.update(inp);
    let hash = hasher.finalize().to_vec();

    let mut out = hash;
    out.extend((size as u32).to_be_bytes());

    let mut path = file.as_ref().to_string_lossy().to_string();
    path.push_str(".cc");

    fs::write(path, out).unwrap();
}

Decompression

Here is where things get a little complicated. We need to try every possible permutation of bytes in the defined size, then check the hash. See what I mean, this is genius.

The equasion for permutations

For decompressing, n is 256 for each bit value and k is the file length. If I put in my Hi\r\n example from before, it would take at most 4,195,023,360 checks to decompress the file. For fun, let’s see how many checks it would be at most for the text 'Hello World\r\n'. So that’s 13 bytes, putting that through the equation gives 14,879,476,555,971,175,569,951,129,600,000. This would probably take many lifetimes running on the world’s best computers to decompress.

And here is the code for decompression:

fn decompress<T>(file: T)
where
    T: AsRef<Path>,
{
    let inp = fs::read(&file).unwrap();

    let parts = inp.split_at(32);
    let mut rdr = Cursor::new(parts.1);
    let size = rdr.read_u32::<BigEndian>().unwrap();

    let hash = parts
        .0
        .iter()
        .map(|b| format!("{:02x}", b))
        .collect::<Vec<String>>()
        .join("");

    println!("Length: {}", size);
    println!("Hash: {}", hash);
    let hash = hash.bytes().collect_vec();

    for i in (0..=255).permutations(size as usize) {
        let mut hasher = Sha256::new();
        hasher.update(&i);
        let this_hash = hasher.finalize().to_vec();

        if this_hash == hash {
            println!("Found!");
            fs::write("OUT.txt", i).unwrap();
            break;
        }
    }
}

💁‍♂️ Conclusion

In conclusion, this was a dumb project. I didn’t really learn anything and unless I’m willing to wait millions of years to decompress a file (im not), it’s not useful.

I guess I should put the source code somewhere if someone is even more insane than me.

Here it is Github Gist