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

Features:

• 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.

Non-goals:

• 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.