cryptogram

A toolset for practicing cryptography

Description

I have always been interested in cryptographic puzzles. When I was beginning to write my first lines of code with my father as my teacher, I discovered in the codebase of one of his projects, a very simple caesar cipher that he used to encrypt dates.

Since then I've come come across the term cryptography in so many places like for example Movies (The Prestige), and even I put together a basic caesar cipher algorithm to encrypt data files which were actually exposed to the filesystem and were read in by a C++ program I wrote to store names of my friends.

I became hungrier for puzzles as I learned about more and more cryptographic algorithms. This project however doesn't provide me with puzzles, but it is definitely helpful while solving them. I mainly find the puzzles at r/codes quite interesting sometimes.

The main idea behind this project was also to break multi layer ciphers, like for example a message encrypted with algorithm A and then algorithm B can be decrypted by just piping the decryption of algorithm B as the input of decryption algorithm A in order to get the original message. More on pipes below.

Installation

1. Clone

   git clone https://github.com/aritra1911/cryptogram.git

2. cd

   cd cryptogram

3. Make sure you got gcc installed.

4. Make

   make all

   or

   make

   To make everything all at once, or put the name of a specific tool like

   make *tool_name*

   For example:

   make vigenere

   Will build and compile the vigenere cipher tool for you, which is a really good cipher.

5. Play

   echo "Happy Birthday" | ./vigenere.out -k liza

Structure of each tool

Each of them primarily reads input from stdin and outputs to stdout, however a specific file could be passed as an optional argument to all of them. The morse tool is a bit different in the sense that it will output the audio directly to a file. I might add an option later to write to stdout so it can be piped to another application to play the code instantly. Is it possible to determine if there is a pipe available at the end? I don't want users to complain about their terminals getting dirty.

Pipes

Say for example you got a code that says:

..-. ...- -... -.-. .--/.-- ..- . .-. -.-. .--. -. .--

You know it's morse code so you put it through the morse tool:

echo "..-. ...- -... -.-. .--/.-- ..- . .-. -.-. .--. -. .--" | ./morse.out -d

You get:

fvbcw wuercpnw

You have a name to serve as the key, you try the vigenere cipher:

echo "fvbcw wuercpnw" | ./vigenere.out -dk liza

You get:

unccl oveguqnl

You are confused that it's not really making any sense and doubting if you're missing a decrytion algorithm in between, but you apply a ROT-13 (a.k.a. caesar cipher with offset 13) anyway.

echo "unccl oveguqnl" | ./caesar.out -do 13

And Lo' behold! You got:

happy birthday

Hopefully none of your friends are this evil that they will encrypt a wish with three layers of encryption.

But all that was not necessary. Yes you figured out the chain, but now you can take the help of pipes to demonstrate your code breaking abilities in just one line:

echo "..-. ...- -... -.-. .--/.-- ..- . .-. -.-. .--. -. .--" | \
    ./morse.out -d | \
    ./vigenere.out -dk liza | \
    ./caesar.out -do 13

And you get:

happy birthday

Pipes are incredible and is something I've taken into deep consideration while building this project, such that all of the tools are capable of inputting or outputting from or to a pipe, respectively. Also this leaves me from programming a lot of jargon that comes with building a proper UI. Have a look at this video where Brian Kernighan shows you how Unix pipes work. He was a really cool guy.

FAQs

Where are the help pages?

On their way! I'm pretty lazy for these kind of things, but I do understand their necessity. The flags are different for different tools and sometimes even I forget how to use them. For now, you can just open the source files and hack your way to reach the flag definitions.

What's wrong with the Morse tool?

I know it's quite buggy and I also have quite poor about explaining my code. It looks really dreadful, I agree. But it's also the tool that I spent most time programming than any other tool in this repo. Even I had to fight my way through in understanding what was exactly happening when I was recently making a change in its core. Eh! I'm sorry, I'm a not a very good programmer. Do you know where I can learn to properly document my code?

Can you explain how the Morse tool works?

Sure! As you might've expected, it's using a binary tree which is serialized in morse/tree.dat. My program simply deserializes the file and make the tree before proceeding to take input. Once the tree is ready, it's quite easy to find the morse code for a character, you just keep pushing a . whenever you take a left branch or a - whenever you take a right. The function for this is recursive and thus makes the code much more efficient. This function is defined in the main morse.c file and is called put_morse. Similarly decryption takes place by finding the character by following a code string, i.e. taking the left branch if the charcter is a . and taking a right when the character is a -. There isn't just another function for this. The demorse function defined in the main file morse.c handles this quite naturally.

For the audio, I did not really wanna code a writer. So I just piped binary data into ffmpeg and turned it into a .wav file. The thing that was previously buggy about this is that the Farnsworth speed could not be exactly followed due to the spaces surrounding / during an interword spacing. So I realized that the spaces weren't serving any real purpose and I removed them and adapted the program accordingly. Now everything should be perfect.

I actually wrote a program for serializing into the file tree.dat, but I considered it as an example of bad code and did not wish to commit. However, you can find it here.

How is your ESP32 Morse Code Transmitter working?

Ref: c24be7aa9596b91dc28b263047cb8f93a580a641

It worked pretty good until I burnt its processor while soldering a cap on the board to automatically trigger flash mode. I bought another one. It's output was current limited for a buzzer so I had to set up a transistor (good ol' 2n3904) circuit in order to get it up and running.