Skip to content

A lightweight, secure, easy-to-use crypto library suitable for constrained environments.


Notifications You must be signed in to change notification settings


Repository files navigation

Build status CodeQL scan Financial Contributors on Open Collective Coverity Scan Build Status TrustInSoft CI


The Hydrogen library is a small, easy-to-use, hard-to-misuse cryptographic library.


  • Consistent high-level API, inspired by libsodium. Instead of low-level primitives, it exposes simple functions to solve common problems that cryptography can solve.
  • 100% built using just two cryptographic building blocks: the Curve25519 elliptic curve, and the Gimli permutation.
  • Small and easy to audit. Implemented as one tiny file for every set of operation, and adding a single .c file to your project is all it takes to use libhydrogen in your project.
  • The whole code is released under a single, very liberal license (ISC).
  • Zero dynamic memory allocations and low stack requirements (median: 32 bytes, max: 128 bytes). This makes it usable in constrained environments such as microcontrollers.
  • Portable: written in standard C99. Supports Linux, *BSD, MacOS, Windows, and the Arduino IDE out of the box.
  • Can generate cryptographically-secure random numbers, even on Arduino boards.
  • Attempts to mitigate the implications of accidental misuse, even on systems with an unreliable PRG and/or no clock.


  • Having multiple primitives serving the same purpose, even to provide compatibility with other libraries.
  • Networking -- but a simple key exchange API based on the Noise protocol is available, and a STROBE-based transport API will be implemented.
  • Interoperability with other libraries.
  • Replacing libsodium. Libhydrogen tries to keep the number of APIs and the code size down to a minimum.

The documentation is maintained in the libhydrogen wiki.

The legacy libhydrogen code (leveraging XChaCha20, SipHashX, BLAKE2SX, Curve25519) remains available in the v0 branch.


Code Contributors

This project exists thanks to all the people who contribute. [Contribute].