Cryptopals in C Code

Solve the Cryptopals Crypto Challenges using pure C.

• This repository contains my implementations, notes, and explanations for each challenge set, focused on clarity, correctness, and learning modern applied cryptography from first principles.

Basically a quiet Saturday and I am in need of a challenge, so I am speedrunning the Cryptopals challenges in C code, just for fun.

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Overview

The Cryptopals Challenges are a well-known set of practical cryptography exercises covering topics like:

• Encoding and decoding
• XOR ciphers
• Block ciphers (AES)
• Padding oracles
• CBC, CTR, stream attacks
• Diffie–Hellman, RSA, and more

This repo is my attempt to solve them from scratch in C, without relying on high-level crypto libraries unless the challenge's intent allows it.

The goal is to deeply understand how the primitives work internally.

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Documentation

There is a doxygen PDF in ./docs

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Third-party dependencies

Unit tests rely on the excellent utest.h project, which is vendored as a Git submodule at third_party/utest.h. After cloning this repository, pull the dependency with:

git submodule update --init --recursive

To refresh the dependency at a later date, run:

git submodule update --remote third_party/utest.h

If your environment blocks outbound network access (as is common in some CI/automation setups), make sure the required utest.h sources are available before attempting to build or run the tests.

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Requirements

• C99 or newer
• Make
• doxygen and pdflatex/texlive environment for docs

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Building & Running

Common combinations of the below:

make clean
make
make test
make docs

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Security Disclaimer

• This code is for my own amusement and educational purposes only.
• Do not use it in production, security-critical, or cryptographic applications.

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References

Cryptopals Challenges