blowfish/README.md

# Blowfish and Blowfish2 Encryption Algorithm

[![Build Status](https://github.com/avinal/blowfish/actions/workflows/cmake.yml/badge.svg)](https://github.com/avinal/blowfish/actions/workflows/cmake.yml)

Blowfish is a symmetric block cipher that can be used as a drop-in replacement for DES or IDEA. It
takes a variable-length key, from 32 bits to 448 bits, making it ideal for both domestic and
exportable use. Blowfish was designed in 1993 by Bruce Schneier as a fast, free alternative to
existing encryption algorithms. Since then it has been analyzed considerably, and it is slowly
gaining acceptance as a strong encryption algorithm. Blowfish is not patented and license-free,
and is available free for all uses.

Blowfish 2 was released in 2005. It has exactly the same design but has twice as many S tables and
uses 64-bit integers instead of 32-bit integers. It no longer works on 64-bit blocks but on 128-bit
blocks like AES. 128-bit block, 64 rounds, key up to 4224 bits.

## About this project

This is a C++ implementation of the encryption algorithm.

## How to use this in your project?

1. You may fork it and use it like any other source file in your project. You only need
[blowfish.hpp](include/blowfish/blowfish.hpp) and [blowfish.cpp](src/blowfish.cpp) files. Just
modify the header as per your convenience.

2. If you are using CMake, the work is lot easier. You can add this as a git submodule. It isolates
your project from this dependency.

  ```bash
    # In your project root type these commands
    git submodule add https://github.com/avinal/blowfish
    # considering this addition is your only change
    git commit -m "blowfish submodule added"
    git push origin main
  ```

Add this to your CMakeLists.txt as well.

## Building

This library has no dependencies on any other code. Just a C++ compiler should be enough to build
this. Although this library is supposed to be used under some other project, sometimes you may need
to build this. Here are the prerequisites:

- [CMake](https://cmake.org/download/)
- [G++](https://gcc.gnu.org/) or [Clang](https://clang.llvm.org/)
- [Make](https://www.gnu.org/software/make/) or [Ninja Build](https://ninja-build.org/) or any other CMake compatible generator.

Here is how I install them on Fedora:

```shell
  sudo dnf install clang cmake g++ make ninja-build
```

Configure CMake, enabled debug for development purposes:

```shell
  cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Debug 
```

Build using configured generator:

```shell
  cmake --build build --config Debug
```

## References

- [Description of a new variable-length key, 64-bit block cipher (Blowfish)](https://link.springer.com/chapter/10.1007/3-540-58108-1_24)
- [The Blowfish Encryption Algorithm](https://www.schneier.com/academic/blowfish/)
- [The Blowfish 2 C Implementation](https://github.com/erwanmilon/blowfish2/)