******************
What is Reticulum?
******************

Reticulum is a cryptography-based networking stack for building both local and
wide-area networks with readily available hardware, that can continue to operate
under adverse conditions, such as extremely low bandwidth and very high latency.

To understand the foundational philosophy and goals of this system, read the
:ref:`Zen of Reticulum <zen>`.

Reticulum allows you to build wide-area networks with off-the-shelf tools, and
offers end-to-end encryption, forward secrecy, autoconfiguring cryptographically
backed multi-hop transport, efficient addressing, unforgeable packet
acknowledgements and more.

From a users perspective, Reticulum allows the creation of applications that
respect and empower the autonomy and sovereignty of communities and individuals.
Reticulum enables secure digital communication that cannot be subjected to
outside control, manipulation or censorship.

Reticulum enables the construction of both small and potentially planetary-scale
networks, without any need for hierarchical or bureaucratic structures to control
or manage them, while ensuring individuals and communities full sovereignty
over their own network segments.

Reticulum is a **complete networking stack**, and does not need IP or higher
layers, although it is easy to utilise IP (with TCP or UDP) as the underlying
carrier for Reticulum. It is therefore trivial to tunnel Reticulum over the
Internet or private IP networks. Reticulum is built directly on cryptographic
principles, allowing resilience and stable functionality in open and trustless
networks.

No kernel modules or drivers are required. Reticulum can run completely in
userland, and will run on practically any system that runs Python 3. Reticulum
runs well even on small single-board computers like the Pi Zero.


Current Status
==============
All core protocol features are implemented and functioning, but additions will probably occur as
real-world use is explored. The API and wire-format can be considered complete and stable, but
could change if absolutely warranted.


Reference Implementation
========================
The Python code, for which this documentation is written, and known as the Reticulum Network Stack,
is the Reference Implementation of Reticulum. The Reticulum Protocol is defined entirely
and authoritatively by this reference implementation, and this manual. It is maintained by Mark Qvist,
identified by the Reticulum Identity ``<bc7291552be7a58f361522990465165c>``.

Compatibility with the Reticulum Protocol is defined as having full interoperability,
and sufficient functional parity with this reference implementation. Any specific protocol
implementation that achieves this is Reticulum. Any that does not is not Reticulum.

The reference implementation is licensed under the :ref:`Reticulum License <license>`.

The Reticulum Protocol was dedicated to the Public Domain in 2016.


What does Reticulum Offer?
==========================

* Coordination-less globally unique addressing and identification

* Fully self-configuring multi-hop routing over heterogeneous carriers

* Flexible scalability over heterogeneous topologies

  * Reticulum can carry data over any mixture of physical mediums and topologies

  * Low-bandwidth networks can co-exist and interoperate with large, high-bandwidth networks

* Initiator anonymity, communicate without revealing your identity

  * Reticulum does not include source addresses on any packets

* Asymmetric X25519 encryption and Ed25519 signatures as a basis for all communication

  * The foundational Reticulum Identity Keys are 512-bit Elliptic Curve keysets

* Forward Secrecy is available for all communication types, both for single packets and over links

* Reticulum uses the following format for encrypted tokens:

  * Ephemeral per-packet and link keys and derived from an ECDH key exchange on Curve25519

  * AES-256 in CBC mode with PKCS7 padding

  * HMAC using SHA256 for authentication

  * IVs are generated through os.urandom()

* Unforgeable packet delivery confirmations

* Flexible and extensible interface system

  * Reticulum includes a large variety of built-in interface types

  * Ability to load and utilise custom user- or community-supplied interface types

  * Easily create your own custom interfaces for communicating over anything

* Authentication and virtual network segmentation on all supported interface types

* An intuitive and easy-to-use API

  * Simpler and easier to use than sockets APIs and simpler, but more powerful

  * Makes building distributed and decentralised applications much simpler

* Reliable and efficient transfer of arbitrary amounts of data

  * Reticulum can handle a few bytes of data or files of many gigabytes

  * Sequencing, compression, transfer coordination and checksumming are automatic

  * The API is very easy to use, and provides transfer progress

* Lightweight, flexible and expandable Request/Response mechanism

* Efficient link establishment

  * Total cost of setting up an encrypted and verified link is only 3 packets, totalling 297 bytes

  * Low cost of keeping links open at only 0.44 bits per second

* Reliable sequential delivery with Channel and Buffer mechanisms


Where can Reticulum be Used?
============================
Over practically any medium that can support at least a half-duplex channel
with greater throughput than 5 bits per second, and an MTU of 500 bytes. Data radios,
modems, LoRa radios, serial lines, AX.25 TNCs, amateur radio digital modes,
ad-hoc WiFi, free-space optical links and similar systems are all examples
of the types of interfaces Reticulum was designed for.

An open-source LoRa-based interface called `RNode <https://unsigned.io/rnode>`_
has been designed as an example transceiver that is very suitable for
Reticulum. It is possible to build it yourself, to transform a common LoRa
development board into one, or it can be purchased as a complete transceiver
from various vendors.

Reticulum can also be encapsulated over existing IP networks, so there's
nothing stopping you from using it over wired Ethernet or your local WiFi
network, where it'll work just as well. In fact, one of the strengths of
Reticulum is how easily it allows you to connect different mediums into a
self-configuring, resilient and encrypted mesh.

As an example, it's possible to set up a Raspberry Pi connected to both a
LoRa radio, a packet radio TNC and a WiFi network. Once the interfaces are
added, Reticulum will take care of the rest, and any device on the WiFi
network can communicate with nodes on the LoRa and packet radio sides of the
network, and vice versa.

Interface Types and Devices
===========================
Reticulum implements a range of generalised interface types that covers the communications hardware that Reticulum can run over. If your hardware is not supported, it's simple to :ref:`implement an interface class<example-custominterface>`. Currently, Reticulum can use the following devices and communication mediums:

* Any Ethernet device

  * WiFi devices

  * Wired Ethernet devices

  * Fibre-optic transceivers

  * Data radios with Ethernet ports

* LoRa using `RNode <https://unsigned.io/rnode>`_

  * Can be installed on `many popular LoRa boards <https://github.com/markqvist/rnodeconfigutil#supported-devices>`_

  * Can be purchased as a `ready to use transceiver <https://unsigned.io/rnode>`_

* Packet Radio TNCs, such as `OpenModem <https://unsigned.io/openmodem>`_

  * Any packet radio TNC in KISS mode

  * Ideal for VHF and UHF radio

* Any device with a serial port

* The I2P network

* TCP over IP networks

* UDP over IP networks

* Anything you can connect via stdio

  * Reticulum can use external programs and pipes as interfaces

  * This can be used to easily hack in virtual interfaces

  * Or to quickly create interfaces with custom hardware

* Anything else using :ref:`custom interface modules<interfaces-custom>` written in Python

For a full list and more details, see the :ref:`Supported Interfaces<interfaces-main>` chapter.

