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.. _understanding-main:
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2021-05-16 17:36:50 +02:00
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***********************
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Understanding Reticulum
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***********************
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This chapter will briefly describe the overall purpose and operating principles of Reticulum, a
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networking stack designed for reliable and secure communication over high-latency, low-bandwidth
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links. It should give you an overview of how the stack works, and an understanding of how to
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develop networked applications using Reticulum.
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This document is not an exhaustive source of information on Reticulum, at least not yet. Currently,
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the best place to go for such information is the Python reference implementation of Reticulum, along
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with the code examples and API reference. It is however an essential resource to understanding the
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general principles of Reticulum, how to apply them when creating your own networks or software.
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After reading this document, you should be well-equipped to understand how a Reticulum network
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operates, what it can achieve, and how you can use it yourself. If you want to help out with the
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development, this is also the place to start, since it will provide a pretty clear overview of the
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sentiments and the philosophy behind Reticulum.
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.. _understanding-motivation:
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Motivation
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==========
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The primary motivation for designing and implementing Reticulum has been the current lack of
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reliable, functional and secure minimal-infrastructure modes of digital communication. It is my
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belief that it is highly desirable to create a cheap and reliable way to set up a wide-range digital
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communication network that can securely allow exchange of information between people and
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machines, with no central point of authority, control, censorship or barrier to entry.
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Almost all of the various networking systems in use today share a common limitation, namely that they
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require large amounts of coordination and trust to work, and to join the networks you need approval
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of gatekeepers in control. This need for coordination and trust inevitably leads to an environment of
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central control, where it's very easy for infrastructure operators or governments to control or alter
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traffic, and censor or persecute unwanted actors.
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Reticulum aims to require as little coordination and trust as possible. In fact, the only
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“coordination” required is to know the characteristics of physical medium carrying Reticulum traffic.
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Since Reticulum is completely medium agnostic, this could be whatever is best suited to the situation.
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In some cases, this might be 1200 baud packet radio links over VHF frequencies, in other cases it might
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be a microwave network using off-the-shelf radios. At the time of release of this document, the
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recommended setup for development and testing is using LoRa radio modules with an open source firmware
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(see the section :ref:`Reference System Setup<understanding-referencesystem>`), connected to a small
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computer like a Raspberry Pi. As an example, the default reference setup provides a channel capacity
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of 5.4 Kbps, and a usable direct node-to-node range of around 15 kilometers (indefinitely extendable
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by using multiple hops).
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.. _understanding-goals:
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Goals
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=====
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To be as widely usable and easy to implement as possible, the following goals have been used to
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guide the design of Reticulum:
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* **Fully useable as open source software stack**
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Reticulum must be implemented with, and be able to run using only open source software. This is
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critical to ensuring the availability, security and transparency of the system.
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* **Hardware layer agnosticism**
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Reticulum shall be fully hardware agnostic, and shall be useable over a wide range
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physical networking layers, such as data radios, serial lines, modems, handheld transceivers,
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wired ethernet, wifi, or anything else that can carry a digital data stream. Hardware made for
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dedicated Reticulum use shall be as cheap as possible and use off-the-shelf components, so
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it can be easily replicated.
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* **Very low bandwidth requirements**
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Reticulum should be able to function reliably over links with a transmission capacity as low
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as *1,000 bps*.
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* **Encryption by default**
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Reticulum must use encryption by default where possible and applicable.
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* **Unlicensed use**
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Reticulum shall be functional over physical communication mediums that do not require any
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form of license to use. Reticulum must be designed in a way, so it is usable over ISM radio
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frequency bands, and can provide functional long distance links in such conditions, for example
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by connecting a modem to a PMR or CB radio, or by using LoRa or WiFi modules.
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* **Supplied software**
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Apart from the core networking stack and API, that allows a developer to build
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applications with Reticulum, a basic communication suite using Reticulum must be
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implemented and released at the same time as Reticulum itself. This shall serve both as a
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functional communication suite, and as an example and learning resource to others wishing
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to build applications with Reticulum.
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* **Ease of use**
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The reference implementation of Reticulum is written in Python, to make it easy to use
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and understand. A programmer with only basic experience should be able to use
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Reticulum in their own applications.
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* **Low cost**
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It shall be as cheap as possible to deploy a communication system based on Reticulum. This
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should be achieved by using cheap off-the-shelf hardware that potential users might already
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own. The cost of setting up a functioning node should be less than $100 even if all parts
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needs to be purchased.
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2021-05-17 11:32:00 +02:00
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.. _understanding-basicfunctionality:
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Introduction & Basic Functionality
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==================================
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Reticulum is a networking stack suited for high-latency, low-bandwidth links. Reticulum is at it’s
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core a *message oriented* system. It is suited for both local point-to-point or point-to-multipoint
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scenarios where alle nodes are within range of each other, as well as scenarios where packets need
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to be transported over multiple hops to reach the recipient.
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Reticulum does away with the idea of addresses and ports known from IP, TCP and UDP. Instead
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Reticulum uses the singular concept of *destinations*. Any application using Reticulum as it’s
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networking stack will need to create one or more destinations to receive data, and know the
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destinations it needs to send data to.
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All destinations in Reticulum are represented internally as 10 bytes, derived from truncating a full
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SHA-256 hash of identifying characteristics of the destination. To users, the destination addresses
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will be displayed as 10 bytes in hexadecimal representation, as in the following example: ``<80e29bf7cccaf31431b3>``.
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By default Reticulum encrypts all data using public-key cryptography. Any message sent to a
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destination is encrypted with that destinations public key. Reticulum can also set up an encrypted
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channel to a destination with *Perfect Forward Secrecy* and *Initiator Anonymity* using a elliptic
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curve cryptography and ephemeral keys derived from a Diffie Hellman exchange on the SECP256R1 curve.
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In Reticulum terminology, this is called a *Link*.
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Reticulum also offers symmetric key encryption for group-oriented communications, as well as
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unencrypted packets for broadcast purposes, or situations where you need the communication to be in
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plain text. The multi-hop transport, coordination, verification and reliability layers are fully
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autonomous and based on public key cryptography.
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Reticulum can connect to a variety of interfaces such as radio modems, data radios and serial ports,
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and offers the possibility to easily tunnel Reticulum traffic over IP links such as the Internet or
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private IP networks.
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2021-05-17 11:32:00 +02:00
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.. _understanding-destinations:
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2021-05-16 17:36:50 +02:00
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Destinations
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------------
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To receive and send data with the Reticulum stack, an application needs to create one or more
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destinations. Reticulum uses three different basic destination types, and one special:
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* **Single**
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The *single* destination type defines a public-key encrypted destination. Any data sent to this
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destination will be encrypted with the destination’s public key, and will only be readable by
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the creator of the destination.
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* **Group**
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The *group* destination type defines a symmetrically encrypted destination. Data sent to this
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destination will be encrypted with a symmetric key, and will be readable by anyone in
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possession of the key. The *group* destination can be used just as well by only two peers, as it
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can by many.
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* **Plain**
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A *plain* destination type is unencrypted, and suited for traffic that should be broadcast to a
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number of users, or should be readable by anyone. Traffic to a *plain* destination is not encrypted.
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* **Link**
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A *link* is a special destination type, that serves as an abstract channel to a *single*
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destination, directly connected or over multiple hops. The *link* also offers reliability and
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more efficient encryption, forward secrecy, initiator anonymity, and as such can be useful even
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when a node is directly reachable.
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.. _understanding-destinationnaming:
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2021-05-16 17:36:50 +02:00
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Destination Naming
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^^^^^^^^^^^^^^^^^^
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Destinations are created and named in an easy to understand dotted notation of *aspects* , and
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represented on the network as a hash of this value. The hash is a SHA-256 truncated to 80 bits. The
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top level aspect should always be a unique identifier for the application using the destination.
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The next levels of aspects can be defined in any way by the creator of the application. For example,
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a destination for a environmental monitoring application could be made up of the application name, a
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device type and measurement type, like this:
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.. code-block:: text
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app name : environmentlogger
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aspects : remotesensor, temperature
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full name : environmentlogger.remotesensor.temperature
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hash : fa7ddfab5213f916dea
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For the *single* destination, Reticulum will automatically append the associated public key as a
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destination aspect before hashing. This is done to ensure only the correct destination is reached,
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since anyone can listen to any destination name. Appending the public key ensures that a given
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packet is only directed at the destination that holds the corresponding private key to decrypt the
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packet.
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**Take note!** There is a very important concept to understand here:
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* Anyone can use the destination name ``environmentlogger.remotesensor.temperature``
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* Each destination that does so will still have a unique destination hash, and thus be uniquely
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addressable, because their public keys will differ.
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In actual use of *single* destination naming, it is advisable not to use any uniquely identifying
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features in aspect naming. Aspect names should be general terms describing what kind of destination
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is represented. The uniquely identifying aspect is always acheived by the appending the public key,
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which expands the destination into a uniquely identifyable one.
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Any destination on a Reticulum network can be addressed and reached simply by knowning its
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destination hash (and public key, but if the public key is not known, it can be requested from the
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network simply by knowing the destination hash). The use of app names and aspects makes it easy to
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structure Reticulum programs and makes it possible to filter what information and data your program
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receives.
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To recap, the different destination types should be used in the following situations:
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* **Single**
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When private communication between two endpoints is needed. Supports multiple hops.
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* **Group**
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When private communication between two or more endpoints is needed. More efficient in
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data usage than *single* destinations. Supports multiple hops indirectly, but must first be
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established through a *single* destination.
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* **Plain**
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When plain-text communication is desirable, for example when broadcasting information.
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To communicate with a *single* destination, you need to know it’s public key. Any method for
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obtaining the public key is valid, but Reticulum includes a simple mechanism for making other
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nodes aware of your destinations public key, called the *announce*. It is also possible to request
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an unknown public key from the network, as all participating nodes serve as a distributed ledger
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of public keys.
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Note that public key information can be shared and verified in many other ways than using the
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built-in methodology, and that it is therefore not required to use the announce/request functionality.
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It is by far the easiest though, and should definitely be used if there is not a good reason for
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doing it differently.
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2021-05-17 11:32:00 +02:00
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.. _understanding-keyannouncements:
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Public Key Announcements
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------------------------
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An *announce* will send a special packet over any configured interfaces, containing all needed
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information about the destination hash and public key, and can also contain some additional,
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application specific data. The entire packet is signed by the sender to ensure authenticity. It is not
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required to use the announce functionality, but in many cases it will be the simplest way to share
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public keys on the network. As an example, an announce in a simple messenger application might
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contain the following information:
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* The announcers destination hash
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* The announcers public key
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* Application specific data, in this case the users nickname and availability status
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* A random blob, making each new announce unique
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* A signature of the above information, verifying authenticity
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With this information, any Reticulum node that receives it will be able to reconstruct an outgoing
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destination to securely communicate with that destination. You might have noticed that there is one
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piece of information lacking to reconstruct full knowledge of the announced destination, and that is
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the aspect names of the destination. These are intentionally left out to save bandwidth, since they
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will be implicit in almost all cases. If a destination name is not entirely implicit, information can be
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included in the application specific data part that will allow the receiver to infer the naming.
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It is important to note that announcements will be forwarded throughout the network according to a
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certain pattern. This will be detailed later.
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Seeing how *single* destinations are always tied to a private/public key pair leads us to the next topic.
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.. _understanding-identities:
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Identities
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----------
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|
In Reticulum, an *identity* does not necessarily represent a personal identity, but is an abstraction that
|
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|
|
|
can represent any kind of *verified entity*. This could very well be a person, but it could also be the
|
|
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|
|
control interface of a machine, a program, robot, computer, sensor or something else entirely. In
|
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|
|
general, any kind of agent that can act, or be acted upon, or store or manipulate information, can be
|
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|
|
represented as an identity.
|
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|
As we have seen, a *single* destination will always have an *identity* tied to it, but not *plain* or *group*
|
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|
|
destinations. Destinations and identities share a multilateral connection. You can create a
|
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|
|
destination, and if it is not connected to an identity upon creation, it will just create a new one to use
|
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|
|
automatically. This may be desirable in some situations, but often you will probably want to create
|
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|
|
the identity first, and then link it to created destinations.
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|
Building upon the simple messenger example, we could use an identity to represent the user of the
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|
|
application. Destinations created will then be linked to this identity to allow communication to
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|
|
reach the user. In such a case it is of great importance to store the user’s identity securely and
|
|
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|
|
privately.
|
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|
|
|
|
2021-05-17 11:32:00 +02:00
|
|
|
|
.. _understanding-gettingfurther:
|
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|
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|
|
2021-05-16 17:36:50 +02:00
|
|
|
|
Getting Further
|
|
|
|
|
---------------
|
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|
The above functions and principles form the core of Reticulum, and would suffice to create
|
|
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|
|
functional networked applications in local clusters, for example over radio links where all interested
|
2021-05-17 11:32:00 +02:00
|
|
|
|
nodes can directly hear each other. But to be truly useful, we need a way to direct traffic over multiple
|
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|
|
hops in the network. In the next sections, two concepts that allow this will be introduced, *paths* and
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|
*links*.
|
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|
|
.. _understanding-transport:
|
2021-05-16 17:36:50 +02:00
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|
|
Reticulum Transport
|
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|
|
|
===================
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|
2021-05-17 11:32:00 +02:00
|
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|
The term routing has been purposefully avoided until now. The current methods of routing used in IP-based
|
|
|
|
|
networks are fundamentally incompatible with the physical link types that Reticulum was designed to handle.
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|
These routing methodologies assume trust at the physical layer, and often needs a lot more bandwidth than
|
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|
|
|
Reticulum can assume is available.
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|
|
Since Reticulum is designed to run over open radio spectrum, no such trust exists, and bandwidth is often
|
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|
|
very limited. Existing routing protocols like BGP or OSPF carry too much overhead to be practically
|
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|
|
useable over bandwidth-limited, high-latency links.
|
2021-05-16 17:36:50 +02:00
|
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|
|
|
|
To overcome such challenges, Reticulum’s *Transport* system uses public-key cryptography to
|
|
|
|
|
implement the concept of *paths* that allow discovery of how to get information to a certain
|
2021-05-17 11:32:00 +02:00
|
|
|
|
destination, and *resources* that help make reliable data transfer more efficient.
|
|
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|
|
|
|
|
|
.. _understanding-paths:
|
2021-05-16 17:36:50 +02:00
|
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|
2021-05-17 11:32:00 +02:00
|
|
|
|
Reaching the Destination
|
|
|
|
|
------------------------
|
2021-05-16 17:36:50 +02:00
|
|
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|
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|
|
In networks with changing topology and trustless connectivity, nodes need a way to establish
|
2021-05-17 11:32:00 +02:00
|
|
|
|
*verified connectivity* with each other. Since the network is assumed to be trustless, Reticulum
|
|
|
|
|
must provide a way to guarantee that the peer you are communicating with is actually who you
|
|
|
|
|
expect. To do this, the following process is employed:
|
2021-05-16 17:36:50 +02:00
|
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|
2021-05-17 11:32:00 +02:00
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|
* | First, the node that wishes to establish connectivity will send out a special packet, that
|
2021-05-16 17:36:50 +02:00
|
|
|
|
traverses the network and locates the desired destination. Along the way, the nodes that
|
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|
|
forward the packet will take note of this *link request*.
|
2021-05-17 11:32:00 +02:00
|
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|
* | Second, if the destination accepts the *link request* , it will send back a packet that proves the
|
2021-05-16 17:36:50 +02:00
|
|
|
|
authenticity of it’s identity (and the receipt of the link request) to the initiating node. All
|
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|
|
nodes that initially forwarded the packet will also be able to verify this proof, and thus
|
|
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|
|
accept the validity of the *link* throughout the network.
|
2021-05-17 11:32:00 +02:00
|
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|
* | When the validity of the *link* has been accepted by forwarding nodes, these nodes will
|
2021-05-16 17:36:50 +02:00
|
|
|
|
remember the *link* , and it can subsequently be used by referring to a hash representing it.
|
2021-05-17 11:32:00 +02:00
|
|
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|
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|
|
* | As a part of the *link request* , a Diffie-Hellman key exchange takes place, that sets up an
|
2021-05-16 17:36:50 +02:00
|
|
|
|
efficient symmetrically encrypted tunnel between the two nodes, using elliptic curve
|
|
|
|
|
cryptography. As such, this mode of communication is preferred, even for situations when
|
|
|
|
|
nodes can directly communicate, when the amount of data to be exchanged numbers in the
|
|
|
|
|
tens of packets.
|
2021-05-17 11:32:00 +02:00
|
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|
* | When a *link* has been set up, it automatically provides message receipt functionality, so the
|
2021-05-16 17:36:50 +02:00
|
|
|
|
sending node can obtain verified confirmation that the information reached the intended
|
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|
|
recipient.
|
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|
|
In a moment, we will discuss the specifics of how this methodology is implemented, but let’s first
|
|
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|
|
recap what purposes this serves. We first ensure that the node answering our request is actually the
|
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|
|
one we want to communicate with, and not a malicious actor pretending to be so. At the same time
|
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|
|
we establish an efficient encrypted channel. The setup of this is relatively cheap in terms of
|
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|
|
bandwidth, so it can be used just for a short exchange, and then recreated as needed, which will also
|
2021-05-17 11:32:00 +02:00
|
|
|
|
rotate encryption keys, but the link can also be kept alive for longer periods of time, if this is
|
|
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|
|
more suitable to the application. The amount of bandwidth used on keeping a link open is practically
|
|
|
|
|
negligible. The procedure also inserts the *link id* , a hash calculated from the link request packet,
|
|
|
|
|
into the memory of forwarding nodes, which means that the communicating nodes can thereafter reach each
|
|
|
|
|
other simply by referring to this *link id*.
|
2021-05-16 17:36:50 +02:00
|
|
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|
|
2021-05-17 11:32:00 +02:00
|
|
|
|
Step 1: Pathfinding
|
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|
|
|
^^^^^^^^^^^^^^^^^^^
|
2021-05-16 17:36:50 +02:00
|
|
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|
|
|
|
The pathfinding method builds on the *announce* functionality discussed earlier. When an announce
|
|
|
|
|
is sent out by a node, it will be forwarded by any node receiving it, but according to some specific
|
|
|
|
|
rules:
|
|
|
|
|
|
|
|
|
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|
2021-05-17 11:32:00 +02:00
|
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|
* | If this announce has already been received before, ignore it.
|
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|
|
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|
|
* | Record into a table which node the announce was received from, and how many times in
|
2021-05-16 17:36:50 +02:00
|
|
|
|
total it has been retransmitted to get here.
|
2021-05-17 11:32:00 +02:00
|
|
|
|
|
|
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|
|
* | If the announce has been retransmitted *m+1* times, it will not be forwarded. By default, *m* is
|
2021-05-16 17:36:50 +02:00
|
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|
|
set to 18.
|
2021-05-17 11:32:00 +02:00
|
|
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|
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|
|
* | The announce will be assigned a delay *d* = c\ :sup:`h` seconds, where *c* is a decay constant, by
|
2021-05-16 17:36:50 +02:00
|
|
|
|
default 2, and *h* is the amount of times this packet has already been forwarded.
|
2021-05-17 11:32:00 +02:00
|
|
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|
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|
|
* | The packet will be given a priority *p = 1/d*.
|
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|
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|
* | If at least *d* seconds has passed since the announce was received, and no other packets with a
|
2021-05-16 17:36:50 +02:00
|
|
|
|
priority higher than *p* are waiting in the queue (see Packet Prioritisation), and the channel is
|
|
|
|
|
not utilized by other traffic, the announce will be forwarded.
|
2021-05-17 11:32:00 +02:00
|
|
|
|
|
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|
|
* | If no other nodes are heard retransmitting the announce with a greater hop count than when
|
2021-05-16 17:36:50 +02:00
|
|
|
|
it left this node, transmitting it will be retried *r* times. By default, *r* is set to 2. Retries follow
|
2021-05-17 11:32:00 +02:00
|
|
|
|
same rules as above, with the exception that it must wait for at least *d* = c\ :sup:`h+1` + t seconds, ie.,
|
2021-05-16 17:36:50 +02:00
|
|
|
|
the amount of time it would take the next node to retransmit the packet. By default, *t* is set to
|
|
|
|
|
10.
|
2021-05-17 11:32:00 +02:00
|
|
|
|
|
|
|
|
|
* | If a newer announce from the same destination arrives, while an identical one is already in
|
2021-05-16 17:36:50 +02:00
|
|
|
|
the queue, the newest announce is discarded. If the newest announce contains different
|
|
|
|
|
application specific data, it will replace the old announce, but will use *d* and *p* of the old
|
|
|
|
|
announce.
|
|
|
|
|
|
|
|
|
|
Once an announce has reached a node in the network, any other node in direct contact with that
|
|
|
|
|
node will be able to reach the destination the announce originated from, simply by sending a packet
|
|
|
|
|
addressed to that destination. Any node with knowledge of the announce will be able to direct the
|
|
|
|
|
packet towards the destination by looking up the next node with the shortest amount of hops to the
|
2021-05-17 11:32:00 +02:00
|
|
|
|
destination.
|
2021-05-16 17:36:50 +02:00
|
|
|
|
|
|
|
|
|
According to these rules and default constants, an announce will propagate throughout the network
|
|
|
|
|
in a predictable way. In an example network utilising the default constants, and with an average link
|
|
|
|
|
distance of *Lavg =* 15 kilometers, an announce will be able to propagate outwards to a radius of 180
|
|
|
|
|
kilometers in 34 minutes, and a *maximum announce radius* of 270 kilometers in approximately 3
|
2021-05-17 11:32:00 +02:00
|
|
|
|
days.
|
2021-05-16 17:36:50 +02:00
|
|
|
|
|
2021-05-17 11:32:00 +02:00
|
|
|
|
Step 2: Link Establishment
|
|
|
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^
|
2021-05-16 17:36:50 +02:00
|
|
|
|
|
|
|
|
|
After seeing how the conditions for finding a path through the network are created, we will now
|
|
|
|
|
explore how two nodes can establish reliable communications over multiple hops. The *link* in
|
|
|
|
|
Reticulum terminology should not be viewed as a direct node-to-node link on the physical layer, but
|
|
|
|
|
as an abstract channel, that can be open for any amount of time, and can span an arbitrary number
|
|
|
|
|
of hops, where information will be exchanged between two nodes.
|
|
|
|
|
|
|
|
|
|
|
2021-05-17 11:32:00 +02:00
|
|
|
|
* | When a node in the network wants to establish verified connectivity with another node, it
|
2021-05-16 17:36:50 +02:00
|
|
|
|
will create a *link request* packet, and broadcast it.
|
2021-05-17 11:32:00 +02:00
|
|
|
|
|
|
|
|
|
* | The *link request* packet contains the destination hash *Hd* , and an asymmetrically encrypted
|
2021-05-16 17:36:50 +02:00
|
|
|
|
part containing the following data: The source hash *Hs* , a symmetric key *Lk* , a truncated
|
|
|
|
|
hash of a random number *Hr* , and a signature *S* of the plaintext values of *Hd* , *Hs* , *Lk* and *Hr*.
|
2021-05-17 11:32:00 +02:00
|
|
|
|
|
|
|
|
|
* | The broadcasted packet will be directed through the network according to the rules laid out
|
2021-05-16 17:36:50 +02:00
|
|
|
|
previously.
|
2021-05-17 11:32:00 +02:00
|
|
|
|
|
|
|
|
|
* | Any node that forwards the link request will store a *link id* in it’s *link table* , along with the
|
2021-05-16 17:36:50 +02:00
|
|
|
|
amount of hops the packet had taken when received. The link id is a hash of the entire link
|
|
|
|
|
request packet. If the path is not *proven* within some set amount of time, the entry will be
|
|
|
|
|
dropped from the table again.
|
2021-05-17 11:32:00 +02:00
|
|
|
|
|
|
|
|
|
* | When the destination receives the link request packet, it will decide whether to accept the
|
2021-05-16 17:36:50 +02:00
|
|
|
|
request. If it is accepted, it will create a special packet called a *proof*. A *proof* is a simple
|
|
|
|
|
construct, consisting of a truncated hash of the message that needs to be proven, and a
|
|
|
|
|
signature (made by the destination’s private key) of this hash. This *proof* effectively verifies
|
|
|
|
|
that the intended recipient got the packet, and also serves to verify the discovered path
|
|
|
|
|
through the network. Since the *proof* hash matches the *path id* in the intermediary nodes’
|
|
|
|
|
*path tables* , the intermediary nodes can forward the proof all the way back to the source.
|
2021-05-17 11:32:00 +02:00
|
|
|
|
|
|
|
|
|
* | When the source receives the *proof* , it will know unequivocally that a verified path has been
|
2021-05-16 17:36:50 +02:00
|
|
|
|
established to the destination, and that information can now be exchanged reliably and
|
|
|
|
|
securely.
|
|
|
|
|
|
|
|
|
|
It’s important to note that this methodology ensures that the source of the request does not need to
|
|
|
|
|
reveal any identifying information. Only the intended destination will know “who called”, so to
|
|
|
|
|
speak. This is a huge improvement to protocols like IP, where by design, you have to reveal your
|
|
|
|
|
own address to communicate with anyone, unless you jump through a lot of hoops to hide it.
|
|
|
|
|
Reticulum offers initiator anonymity by design.
|
|
|
|
|
|
|
|
|
|
When using *links* , Reticulum will automatically verify anything sent over the link, and also
|
|
|
|
|
automates retransmissions if parts of a message was lost along the way. Due to the caching features
|
|
|
|
|
of Reticulum, such a retransmission does not need to travel the entire length of an established path.
|
|
|
|
|
If a packet is lost on the 8th hop of a 12 hop path, it can be fetched from the last hop that received it
|
|
|
|
|
reliably.
|
|
|
|
|
|
2021-05-17 11:32:00 +02:00
|
|
|
|
.. _understanding-resources:
|
2021-05-16 17:36:50 +02:00
|
|
|
|
|
2021-05-17 11:32:00 +02:00
|
|
|
|
Resources
|
|
|
|
|
---------
|
2021-05-16 17:36:50 +02:00
|
|
|
|
|
2021-05-17 11:32:00 +02:00
|
|
|
|
TODO: Write
|
2021-05-16 17:36:50 +02:00
|
|
|
|
|
|
|
|
|
In traditional networks, large amounts of data is rapidly exchanged with very low latency. Links of
|
|
|
|
|
several thousand kilometers will often only have round-trip latency in the tens of milliseconds, and
|
|
|
|
|
as such, traditional protocols are often designed to not store any transmitted data at intermediary
|
|
|
|
|
hops. If a transmission error occurs, the sending node will simply notice the lack of a packet
|
|
|
|
|
acknowledgement, and retransmit the packet all the way, until it hears back from the receiver that it
|
|
|
|
|
got the intended data.
|
|
|
|
|
|
|
|
|
|
In bandwidth-limited and high-latency conditions, such behaviour quickly causes congestion on the
|
|
|
|
|
network, and communications that span many hops become exceedingly expensive in terms of
|
|
|
|
|
bandwidth usage, due to the higher risk of some packets failing.
|
|
|
|
|
|
|
|
|
|
Reticulum alleviates this in part with it’s *path* discovery methodology, and in part by implementing
|
|
|
|
|
*resource* caching at all nodes that can support it. Network operation can be made much more
|
|
|
|
|
efficient by caching everything for a period of time, and given the availability of cheap memory and
|
|
|
|
|
storage, this is a very welcome tradeoff. A gigabyte of memory can store millions of Reticulum
|
|
|
|
|
packets, and since everything is encrypted by default, the storing poses very little privacy risk.
|
|
|
|
|
|
|
|
|
|
In a Reticulum network, any node that is able to do so, should cache as many packets as it’s
|
|
|
|
|
memory will allow for. When a packet is received, a timestamp and a hash of the packet is stored
|
|
|
|
|
along with the full packet itself, and it will be kept in storage until the allocated cache storage is
|
|
|
|
|
full, whereupon the packet that was last accessed in the cache will be deleted. If a packet is accessed
|
|
|
|
|
from the cache, it’s timestamp will be updated to the current time, to ensure that packets that are
|
|
|
|
|
used stay in the cache, and packets that are not used are dropped from memory.
|
|
|
|
|
|
|
|
|
|
Some packet types are stored in separate caching tables, that allow easier lookup for other nodes.
|
|
|
|
|
For example, an announce is stored in a way, that allows other nodes to request the public key for a
|
|
|
|
|
certain destination, and as such the network as a whole operates as a distributed key ledger.
|
|
|
|
|
|
|
|
|
|
For more details on how the caching works and is used, see the reference implementation source
|
|
|
|
|
code.
|
|
|
|
|
|
2021-05-17 11:32:00 +02:00
|
|
|
|
.. _understanding-referencesystem:
|
|
|
|
|
|
2021-05-16 17:36:50 +02:00
|
|
|
|
Reference System Setup
|
|
|
|
|
======================
|
|
|
|
|
|
|
|
|
|
This section will detail the recommended *Reference System Setup* for Reticulum. It is important to
|
|
|
|
|
note that Reticulum is designed to be usable over more or less any medium that allows you to send
|
|
|
|
|
and receive data in a digital form, and satisfies some very low minimum requirements. The
|
|
|
|
|
communication channel must support at least half-duplex operation, and provide an average
|
|
|
|
|
throughput of around 1000 bits per second, and supports a physical layer MTU of 500 bytes. The
|
2021-05-16 19:18:21 +02:00
|
|
|
|
Reticulum software should be able to run on more or less any hardware that can provide a Python 3.x
|
2021-05-16 17:36:50 +02:00
|
|
|
|
runtime environment.
|
|
|
|
|
|
|
|
|
|
That being said, the reference setup has been outlined to provide a common platform for anyone
|
|
|
|
|
who wants to help in the development of Reticulum, and for everyone who wants to know a
|
|
|
|
|
recommended setup to get started. A reference system consists of three parts:
|
|
|
|
|
|
|
|
|
|
* **A channel access device**
|
|
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Or *CAD* , in short, provides access to the physical medium whereupon the communication
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takes place, for example a radio with an integrated modem. A setup with a separate modem
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connected to a radio would also be termed a “channel access device”.
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* **A host device**
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Some sort of computing device that can run the necessary software, communicates with the
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channel access device, and provides user interaction.
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* **A software stack**
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The software implementing the Reticulum protocol and applications using it.
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The reference setup can be considered a relatively stable platform to develop on, and also to start
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building networks on. While details of the implementation might change at the current stage of
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development, it is the goal to maintain hardware compatibility for as long as entirely possible, and
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the current reference setup has been determined to provide a functional platform for many years
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into the future. The current Reference System Setup is as follows:
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* **Channel Access Device**
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A data radio consisting of a LoRa radio module, and a microcontroller with open source
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firmware, that can connect to host devices via USB. It operates in either the 430, 868 or 900
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MHz frequency bands. More details can be found on the `RNode Page <https://unsigned.io/rnode>`_.
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* **Host device**
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Any computer device running Linux and Python. A Raspberry Pi with a Debian based OS is
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recommended.
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* **Software stack**
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The current Reference Implementation Release of Reticulum, running on a Debian based
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operating system.
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It is very important to note, that the reference channel access device **does not** use the LoRaWAN
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standard, but uses a custom MAC layer on top of the plain LoRa modulation! As such, you will
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need a plain LoRa radio module connected to an MCU with the correct firmware. Full details on how to
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get or make such a device is available on the `RNode Page <https://unsigned.io/rnode>`_.
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With the current reference setup, it should be possible to get on a Reticulum network for around 100$
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even if you have none of the hardware already, and need to purchase everything.
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2021-05-17 11:32:00 +02:00
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.. _understanding-protocolspecifics:
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Protocol Specifics
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==================
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This chapter will detail protocol specific information that is essential to the implementation of
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Reticulum, but non critical in understanding how the protocol works on a general level. It should be
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treated more as a reference than as essential reading.
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Node Types
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----------
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Currently Reticulum defines two node types, the *Station* and the *Peer*. A node is a *station* if it fixed
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in one place, and if it is intended to be kept online most of the time. Otherwise the node is a *peer*.
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This distinction is made by the user configuring the node, and is used to determine what nodes on the
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network will help forward traffic, and what nodes rely on other nodes for connectivity.
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If a node is a *Peer* it should be given the configuration directive ``enable_transport = No``.
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If it is a *Station*, it should be given the configuration directive ``enable_transport = Yes``.
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Packet Prioritisation
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---------------------
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Currently, Reticulum is completely priority-agnostic regarding general traffic. All traffic is handled
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on a first-come, first-serve basis. Announce re-transmission are handled according to the re-transmission
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times and priorities described earlier in this chapter.
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2021-05-17 11:32:00 +02:00
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It is possible that a prioritisation engine could be added to Reticulum in the future, but in
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the light of Reticulums goal of equal access, doing so would need to be the subject of careful
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investigation of the consequences first.
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2021-05-16 17:36:50 +02:00
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Binary Packet Format
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--------------------
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|
2021-05-17 11:32:00 +02:00
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.. code-block:: text
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|
== Reticulum Wire Format ======
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A Reticulum packet is composed of the following fields:
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[HEADER 2 bytes] [ADDRESSES 10/20 bytes] [CONTEXT 1 byte] [DATA 0-477 bytes]
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* The HEADER field is 2 bytes long.
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* Byte 1: [Header Type], [Propagation Type], [Destination Type] and [Packet Type]
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* Byte 2: Number of hops
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* The ADDRESSES field contains either 1 or 2 addresses.
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* Each address is 10 bytes long.
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* The Header Type flag in the HEADER field determines
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whether the ADDRESSES field contains 1 or 2 addresses.
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* Addresses are Reticulum hashes truncated to 10 bytes.
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* The CONTEXT field is 1 byte.
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* It is used by Reticulum to determine packet context.
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* The DATA field is between 0 and 477 bytes.
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* It contains the packets data payload.
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Header Types
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|
-----------------
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|
type 1 00 Two byte header, one 10 byte address field
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type 2 01 Two byte header, two 10 byte address fields
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type 3 10 Reserved
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|
type 4 11 Reserved
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|
Propagation Types
|
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|
-----------------
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|
broadcast 00
|
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|
transport 01
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|
reserved 10
|
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|
reserved 11
|
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|
Destination Types
|
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|
|
-----------------
|
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|
|
single 00
|
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|
|
group 01
|
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|
|
plain 10
|
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|
link 11
|
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|
|
Packet Types
|
|
|
|
|
-----------------
|
|
|
|
|
data 00
|
|
|
|
|
announce 01
|
|
|
|
|
link request 10
|
|
|
|
|
proof 11
|
|
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|
|
+- Packet Example -+
|
|
|
|
|
|
|
|
|
|
HEADER FIELD ADDRESSES FIELD CONTEXT FIELD DATA FIELD
|
|
|
|
|
_______|_______ ________________|________________ ________|______ __|_
|
|
|
|
|
| | | | | | | |
|
|
|
|
|
01010000 00000100 [ADDR1, 10 bytes] [ADDR2, 10 bytes] [CONTEXT, 1 byte] [DATA]
|
|
|
|
|
| | | | |
|
|
|
|
|
| | | | +-- Hops = 4
|
|
|
|
|
| | | +------- Packet Type = DATA
|
|
|
|
|
| | +--------- Destination Type = SINGLE
|
|
|
|
|
| +----------- Propagation Type = TRANSPORT
|
|
|
|
|
+------------- Header Type = HEADER_2 (two byte header, two address fields)
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
+- Packet Example -+
|
|
|
|
|
|
|
|
|
|
HEADER FIELD ADDRESSES FIELD CONTEXT FIELD DATA FIELD
|
|
|
|
|
_______|_______ _______|_______ ________|______ __|_
|
|
|
|
|
| | | | | | | |
|
|
|
|
|
00000000 00000111 [ADDR1, 10 bytes] [CONTEXT, 1 byte] [DATA]
|
|
|
|
|
| | | | |
|
|
|
|
|
| | | | +-- Hops = 7
|
|
|
|
|
| | | +------- Packet Type = DATA
|
|
|
|
|
| | +--------- Destination Type = SINGLE
|
|
|
|
|
| +----------- Propagation Type = BROADCAST
|
|
|
|
|
+------------- Header Type = HEADER_1 (two byte header, one address field)
|