toxcore

Toxcore is a C library that provides the networking and cryptography foundation for the Tox communication protocol. Tox was created as a response to concerns about centralized communication services and government surveillance programs, with the explicit goal of letting people send messages, share files, and make video calls without routing anything through a company's servers.

The system is fully peer-to-peer: instead of routing traffic through a central service, it connects users directly to each other. Every user gets a unique identifier called a Tox ID, which is derived from a public key. To find someone on the network, Tox uses a distributed lookup mechanism similar to how BitTorrent locates files, so no single server holds a directory of everyone's addresses.

Connections between peers are encrypted end-to-end. Once two users are connected, they can exchange text messages, transfer files, and start video chats, all over an encrypted channel. No account registration is required: you share your Tox ID with someone and they can add you directly.

For network connectivity, Tox prefers direct UDP connections because UDP allows a technique called hole punching, which lets two computers behind typical home or office routers find each other without manual configuration. When a firewall prevents that, the library falls back to TCP relay servers as an alternative path.

Toxcore is the core library only. It does not include a user interface. Separate client applications built on top of it are available for different platforms, with links listed on the project wiki. Installing it requires compiling from source.