libnostr-c

A lightweight, portable C library for the Nostr protocol with native Lightning Network integration

What is libnostr-c?

A high-performance C implementation of the Nostr protocol built for efficiency and minimal dependencies. libnostr-c provides core event management, modern NIP-44 encryption powered by noscrypt, Lightning zaps, WebSocket relay communication, and complete relay-side protocol support. Designed for both client applications and relay implementations, with a focus on security, portability, and embedded systems.

API Example

// Client-side
nostr_init();
nostr_keypair_generate();
nostr_event_create();
nostr_event_sign();
nostr_nip44_encrypt();
nostr_relay_connect();

// Relay-side (for relay implementations)
nostr_client_msg_parse();
nostr_filter_matches();
nostr_event_validate_full();
nostr_deletion_authorized();
nostr_relay_msg_serialize();
nostr_relay_info_serialize();

Motivation

Building nostr applications in C requires reliable, efficient cryptographic operations and protocol handling. libnostr-c provides a complete implementation with modern NIP-44 encryption, Lightning integration, and minimal resource requirements. Built with security-first design principles and optimized for both desktop and embedded systems.

Platform Support

The following table lists supported platforms and cryptographic backends:

Platform	Crypto Backend	Notes	CI Status
Linux	noscrypt, secp256k1	GCC/Clang	✅ Tested
macOS	noscrypt, secp256k1	Clang	✅ Tested
Windows	noscrypt, secp256k1	MSVC	✅ Tested
ESP-IDF	noscrypt, mbedtls	ESP32/S2/S3/C3/C6, v5.0+	✅ Tested

Getting started

Please use the following links to obtain packages and extended documentation.

Documentation
Examples
Performance Analysis

Super quick start

Prerequisites:

• CMake 3.16+, C99 compiler, OpenSSL
• secp256k1, libcjson, libwebsockets (see BUILDING.md)

git clone https://github.com/privkeyio/libnostr-c.git
cd libnostr-c
mkdir build && cd build
cmake ..
make -j$(nproc)
sudo make install

For detailed installation instructions, dependency management, and platform-specific setup, see docs/BUILDING.md.

Notes

Builds

Automated builds and releases are available through GitHub Actions CI/CD.

Features

libnostr-c supports modular compilation - build only what you need:

• Core NIPs (01, 02, 05, 06, 10, 13, 18, 19, 21, 25, 57, 65) enabled by default
• Optional NIPs (04, 09, 11, 17, 26, 40, 44, 45, 46, 47, 49, 50, 51, 59) via feature flags
• NIP-11 relay information document for serving relay metadata
• Relay protocol support for building relay implementations
• Modern noscrypt backend provides NIP-44 encryption
• Fallback to secp256k1 for basic operations

Projects Using libnostr-c

• keep-esp32 - Air-gapped ESP32-S3 FROST threshold signing device with Nostr DKG coordination
• wisp-esp32 - Minimal ESP32-S3 Nostr relay with 21-day ephemeral storage
• whisper - Encrypted DM pipe for Nostr using NIP-17 + NIP-44, Unix-style CLI
• vain - High-performance vanity Nostr public key miner

License

The software in this repository is licensed under MIT. See the LICENSE file for details.

Acknowledgments

This project is powered by noscrypt for high-performance cryptographic operations and NIP-44 encryption.