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libharpia (Unofficial - Work In Progress)

This repository contains a Python-based simulation of the libharpia cryptographic library, originally developed to secure Brazilian elections by CEPESC¹. The code simulates key cryptographic operations, such as hybrid key exchange, authenticated encryption, digital signatures, and key derivation using modern cryptographic algorithms available in Python.

Disclaimer 1: I started the implementation but hadn't got time to finish. It is still a work in progress with unfortunately no end in sight (due to my other commitments). The functions are not yet finished and do not implement all primitives as stated. I had to adapt a little to get a runnable code.

Disclaimer 2: This is a NON-OFFICIAL implementation because shamefully, the Brazilian government ignores Kerckhoffs's principle ("the security of a cryptographic system shouldn't rely on the secrecy of the algorithm") and does not allow public auditing.

Features

  • Hybrid Key Exchange (Simulated): Uses elliptic curve Diffie-Hellman (ECDH) to generate a shared encryption key.
  • Authenticated Encryption: Implements ChaCha20-Poly1305 for encryption, ensuring both confidentiality and integrity.
  • Digital Signatures: Uses Ed448 elliptic curve cryptography to sign messages.
  • Key Derivation: Uses the HKDF algorithm to derive cryptographic keys from a base key, salt, and additional info.

Installation

  1. Clone the repository:
git clone https://github.com/AndreisPurim/libharpia.git
cd libharpia
  1. Install the necessary dependencies:
pip install pynacl cryptography

Usage

The main script apis.py demonstrates the key functionalities, simulating the API calls (originally not programmed in python):

  • init_encryption(k, NULL, 0, ct, ctl, pk, NULL): Initializes the encryption key using elliptic curve Diffie-Hellman and HKDF.
  • encrypt(k, p, pl, c, cl, NULL): Encrypts the plaintext using ChaCha20-Poly1305 authenticated encryption.
  • sign_buffer(b, bl, s, sl, pk): Signs a message buffer using the Ed448 digital signature algorithm.
  • derive_key(sk, dk, salt, saltl, info, infol, NULL): Derives a new key using the HKDF key derivation function.

Cryptographic Concepts

This simulation uses Python cryptographic libraries to mimic libharpia's core concepts:

  • Elliptic Curve Diffie-Hellman (ECDH): A public-key cryptographic key exchange method used to securely generate a shared encryption key.
  • ChaCha20-Poly1305: A stream cipher combined with a Message Authentication Code (MAC) for authenticated encryption.
  • Ed448 Digital Signatures: A signature algorithm that provides strong security and is part of modern cryptographic standards.
  • HKDF (HMAC-based Key Derivation Function): A cryptographic algorithm that derives secure keys from a shared secret, salt, and additional information. (Note to self: I'm yet to reread the paper and understand how their KDF differs from HKDF).

License

This project is licensed under the MIT License.

Acknowledgements

Thanks to the authors of the original paper.

[1] 1. Rodrigo Pacheco, Douglas Braga, Iago Passos, Thiago Araújo, Vinícius Lagrota, and Murilo Coutinho. 2022. libharpia: a New Cryptographic Library for Brazilian Elections. Anais do XXII Simpósio Brasileiro de Segurança da Informação e de Sistemas Computacionais (SBSeg 2022), 250–263. https://doi.org/10.5753/sbseg.2022.224098