Invisible Internet Project (I2P)

Introduction

Network

The Invisible Internet Project (I2P) homepage ^[archive] provides a simple overview of the protocol:

I2P is an anonymous network built on top of the internet. It allows users to create and access content and build online communities on a network that is both distributed and dynamic. It is intended to protect communication and resist monitoring by third parties such as ISPs.

Aside from anonymizing traffic within the network, I2P functions with the same capabilities as the Internet, however its design and decentralization create a censorship resistant environment for the free-flow of information.

Mirrored sites hosted on the network allow access to news outlets and other resources in areas where information is being filtered or denied. Online communities wishing to organize in restrictive environments can do so anonymously to mitigate political threat and protect each other.

The I2P anonymous network exposes a simple layer that applications can use to anonymously and securely send messages to each other through "tunnels". The network itself is strictly message-based (IP), but there is a library available to allow reliable streaming communication on top of it (TCP). All communication is encrypted end-to-end -- in total there are four layers of encryption used when sending a message -- and even the end points ("destinations") are cryptographic identifiers (essentially a pair of public keys).

This design is known as garlic routing ^[archive] which is a variant of onion routing ^[archive] (used in the Tor network) and benefits from the research on the latter but makes some different tradeoffs. Each client application has their own I2P 'router' that finds other clients by querying against the fully distributed 'network database' - a custom structured distributed hash table (DHT) based on the Kademlia algorithm ^[archive]. Every router transports traffic for its peers which it uses as cover traffic for its own. To learn more about I2P technical details, see here ^[archive].

In contrast to the Tor network, I2P is focused on creating a community around P2P darknet services rather than providing "outproxies"(exits) to the clearnet. The I2P development team ^[archive] is an open group that welcomes all parties who are interested in getting involved ^[archive]. All the code is open source ^[archive]. The core I2P Software Development Kit (SDK) and the current router implementation is accomplished in Java, and there is a simple socket based API ^[archive] for accessing the network from other languages (with a C library available, and both Python and Perl in development). The network is actively being developed and has not yet reached the 1.0 release, but the current roadmap ^[archive] describes their active schedule.

Tor vs I2P

Many of Tor's concepts have (virtual) equivalents in I2P, despite the terminology ^[archive] being somewhat different.

Table: Tor vs. I2P Terminology

Tor Terminology	I2P Equivalent
Cell	Message
Circuit	Tunnel
Client	Router or Client
Directory	NetDb
Directory Server	Floodfill Router
Entry Guards	Fast Peers
Entry Node	Inproxy
Exit Node	Outproxy
Hidden (Onion) Service	Hidden Service, Eepsite or Destination
Hidden Service Descriptor	LeaseSet
Hidden Service 'Stealth Mode'	I2P Client Whitelist or Encrypted LeaseSets
Introduction Point	Inbound Gateway
Node	Router
Onion Proxy	I2PTunnel Client (more or less)
Relay	Router
Rendezvous Point	Similar to Inbound Gateway + Outbound Endpoint
Router Descriptor	RouterInfo
Server	Router
Single Onion Service	I2P 0-hop Tunnel

The I2P comparison page notes the relative strengths of Tor and I2P; those are summarized below.

Tor's primary strengths are: a larger user base; greater academic interest and research; significant funding; a large development team; greater resistance to state-level censorship (TLS transport and bridges); large number of exit nodes; better memory usage; thorough documentation; low client bandwidth overhead; higher throughput and lower latency.

In comparison, I2P's primary strengths are: optimization for hidden services; a fully distributed design; better peer selection; varied and untrusted directory servers; peer-to-peer friendly nature; improved load balancing and resilience; unidirectional tunnels; protection against client activity detection; short-lived tunnels; low bandwidth overhead for full peers; TCP and UDP transports; and being based on the Java programming language.

How-to: Use I2P in Whonix

There are two methods of using I2P in Whonix ™:

1. Inproxies inside Whonix-Workstation; or
2. I2P client inside Whonix-Workstation (recommended)

The inproxy method is better suited for causal use of I2P. In this instance, users just want to anonymously view an Eepsite and are not concerned about eavesdroppers so long as anonymity is assured.

It is safer to use the I2P client inside Whonix ™, since all I2P traffic is tunneled through Tor and access is fully featured. This is a little more difficult than installing I2P the ordinary way, that is using I2P in the clear, not over Tor.

Readers who are considering using I2P in Whonix ™ are suggested to review the related forum thread ^[archive].

Inproxies inside Whonix-Workstation

There are several I2P inproxies and they have similar functionality to Tor2web ^[archive]. Simply use Tor Browser which is installed in Whonix ™ by default to directly access the I2P proxies listed.

Although this is the easiest method, on the downside end-to-end encryption is lost when connecting to the eepsites. This is not the case when I2P is installed directly inside Whonix-Workstation ™ or if I2P is used in the ordinary way. Further, potentially Tor Exit Nodes can Eavesdrop on Communications if an inproxy uses plain http, since it is an unencrypted connection. This risk is averted if the inproxy uses https or is reachable via an onion service. In any case, the I2P inproxy administrator can see all of your traffic in the I2P network and it is impossible to prevent that.

Example list of I2P inproxy domains (in bold):

• http://forum.i2p.rocks ^[archive]
• http://forum.i2p.re ^[archive]
• http://forum.i2p.xyz ^[archive]
• http://forum.i2p2piszzzndhfvr.onion ^[archive]
• https://www.hiddenservice.net/ ^[archive]
• Many others are down at the time of writing; see footnotes.

I2P Client inside Whonix-Workstation

Introduction

The preferred configuration is to connect to Tor before I2P inside Whonix-Workstation ™: user → Tor → I2P → Internet

Before configuring this tunnel link, it is recommended to read the following related wiki entries:

• Combining Tunnels with Tor
• Connecting to Tor before a Proxy

Post-Tor I2P Tunnel Effects

Table: Post-Tor I2P Connections

Domain	Information
Advantages	Anonymity is provided by Tor. The I2P router console [archive] works normally inside Tor Browser. There is no need to install a graphical user interface on Whonix-Gateway ™. Eepsites (.i2p) can be reached directly from Tor Browser. I2P's end-to-end encryption will be used as usual.
Disadvantages	Adds load to Tor. Adds load to I2P. This is slower than using I2P directly on Whonix-Gateway ™ or the ordinary configuration. No contributions are provided to the I2P network ('leeching').
Warning: No Stream-isolation Support	I2P does not have stream isolation support which means that visits to Eepsites are linkable and fingerprintable -- each request includes the same X-I2P-Dest* headers, which are unique to each user. This might be true for outproxy requests as well. If you access site1.i2p followed by site2.i2p, site3.i2p and so on, each one of those operators will see the exact same X-I2P-Dest* values. This means if they are colluding, they will know that the same person accessed all of them. I2P operators can build a more detailed profile the longer I2P is left running. The X-I2P-Dest* values only change upon restart of the I2P instance or when the HTTP Proxy tunnel is stopped/started. I2P does not have a fix for this at present, however an experimental plugin is being written to provide a stream-isolating mechanism for http-over-I2P, see: eeProxy [archive].

Installation and Setup

Note:

• A large number of dependencies are required for this procedure, so a separate (cloned) Whonix-Workstation ™ (Qubes-Whonix ™: whonix-ws-15-clone-1 TemplateVM) is recommended.
• Privoxy ^[archive] and about:config changes in Tor Browser worsen the browser fingerprint. The modified Tor Browser should only be used for I2P purposes.
  • In Qubes-Whonix ™, a separate anon-whonix-I2P AppVM is recommended.
• If I2P is non-functional, report any issues in the i2p inside Whonix-Workstation broken ^[archive] forum thread.

1. Update the package lists. (Qubes-Whonix ™: whonix-ws-15-clone-1 TemplateVM).

sudo apt-get update

sudo apt-get update

2. Install I2P and dependencies.

sudo apt-get install i2p

sudo apt-get install i2p

3. Install Privoxy.

sudo apt-get install privoxy

sudo apt-get install privoxy

4. Add I2P forwarding to the Privoxy configuration file.

sudoedit /etc/privoxy/config

sudoedit /etc/privoxy/config

At the bottom of the configuration file, add.

forward .i2p 127.0.0.1:4444

Save and exit.

5. Configure I2P.

sudo dpkg-reconfigure i2p

sudo dpkg-reconfigure i2p

The following settings are recommended:

• leave the user as i2psvc
• have I2P run as a daemon when starting (the service will automatically run when the system boots)
• apply the Debian AppArmor profile
• leave the default RAM setting as 128MB

In Qubes-Whonix ™, shut down the TemplateVM.

6. Configure Tor Browser to allow connections to I2P (Qubes-Whonix ™: anon-whonix-I2P AppVM).

Note: The following steps will no longer be required once Whonix releases a custom Tor Browser for connecting to alternative networks.

Warning:

• This step changes the web fingerprint of Tor Browser!
• Leave all other settings as is!

In Tor Browser, type about:config into the URL bar and press Enter. Make the following changes:

• extensions.torbutton.use_nontor_proxy true
• network.proxy.share_proxy_settings true
• network.proxy.http 127.0.0.1
• network.proxy.http_port 8118
• network.proxy.no_proxies_on 1
• network.proxy.socks_remote_dns false

7. Optional: Start/stop/check the I2P service.

This step is unnecessary if I2P was set to automatically run as a daemon.

To start the I2P service, run.

sudo systemctl start i2p

sudo systemctl start i2p

To stop the I2P service, run.

sudo systemctl stop i2p

sudo systemctl stop i2p

To check the status of the I2P service, run.

sudo systemctl status i2p

sudo systemctl status i2p

Before using I2P, it is recommended to access the I2P router configuration and make several adjustments for better performance.

Usage

Open I2P router console ^[archive] in Tor Browser (Qubes-Whonix ™: anon-whonix-I2P AppVM).

http://127.0.0.1:7657

http://127.0.0.1:7657

Figure: I2P Router Console

Recommendation:

• set your preferred language
• allow the network bandwidth test to complete (takes 60 seconds)
• review and adjust the bandwidth settings
  • the default settings of 300 KB/s down / 60 KB/s up are fairly conservative
  • users report settings of 5000+ KB/s provide better connectivity
• on the network configuration page, set "Prefer IPv4 over IPv6" and "Completely disable" the UDP port and save the changes

If errors appear like: "Network: ERR-UDP Disabled and Inbound TCP host/port not set" or "ERR-Clock Skew of X min", they can be safely ignored.

Note that once the Local Tunnels (shared clients) section shows a green connection, I2P should be fully functional and it is possible to browse eepsites like echelon.i2p. Some users report this process can be lengthy and take more than 10 minutes before the tunnels are stable/available.

Searching I2P

Search engines:

• The onion service search engine https://ahmia.fi ^[archive] now supports I2P eepsites and Tor2Web plans on adding I2P support.
• http://seeker.i2p ^[archive] is a search engine for I2P eepsites.

Eepsite directories:

• http://stats.i2p ^[archive] lists registered i2p websites.
• http://identiguy.i2p ^[archive] lists many known and alive I2P websites.
• http://no.i2p ^[archive] lists known latest and alive i2p websites. The site list is generated from registered sites and external sources.
• http://inr.i2p ^[archive] lists known latest and alive i2p websites. The site list is generated from registered sites and external sources.

Figure: I2P Browsing in Whonix ™

Services

The I2P supported applications webpage ^[archive] warns that no guarantee can be provided about the safety of compatible applications, plugins and services -- they must be properly configured and might jeopardize anonymity due to design faults or carelessness. Carefully vet these tools and research them diligently beforehand.

Many interesting features and functionality are implemented for I2P in the form of stand-alone packages or plugins that can be optionally installed from their official plugin eepsite ^[archive]. Various tools are available for:

• blogging, forums and wikis
• decentralized file storage
• development tools
• domain naming
• email
• file sharing
• network administration
• real-time chat
• web browsing
• website hosting

The instructions are simple to follow. The signing keys for these plugins are already built into the official I2P package and so are already white-listed. This is not a complete list.

For documentation about default port numbers of I2P plugins, see this page ^[archive].

I2P-Bote

I2P-Bote ^[archive] is a serverless, encrypted email plugin that uses I2P for anonymity. Messages are stored in the distributed hash table (DHT) ^[archive] for 100 days, during which the recipient is able to download them. Emails are automatically encrypted and digitally signed, which means only the intended recipient can read them and they cannot be forged by third parties.

To back up I2P-Bote data, copy the i2pbote folder inside the I2P config directory (~/.i2p/i2pbote on Unix systems or /var/lib/i2p/i2p-config when running as a daemon).

Compartmentalize activities and only use the I2P-Bote/Susimail VM snapshot for this purpose. Generally, applications that run with a browser interface are vulnerable to a whole class of bugs, including cross-site request forgery (CSRF) ^[archive].

Features

• themeable webmail interface
• user interface translated into many languages
• one-click creation of email accounts (called email identities)
• emails can be sent under a sender identity, or anonymously
• ElGamal, Elliptic Curve, and NTRU encryption
• encryption and signing is transparent, without the need to know about PGP
• delivery confirmation
• basic support for short recipient names
• IMAP / SMTP

Planned Features

• custom folders
• sending and receiving via relays, similar to Mixmaster
• lots of small improvements

RetroShare

RetroShare is a friend-to-friend ^[archive] (F2F) network that enables end-to-end encrypted communications, including general messaging, mail, forums, publish-subscribe messaging ('pubsub'), file exchange and even telephony. It can be used as an alternative to Syndie (see further below) and can be tunneled through I2P for enhanced anonymity.

Follow the steps in this guide ^[archive] to connect to others over I2P. Also see: I2P Hidden RetroShare Nodes ^[archive].

To install RetroShare, see: Installation.

Syncthing

Syncthing ^[archive] is a popular libre software for file syncing based on the bittorrent protocol. Syncthing provides several benefits:

• cross-platform availability
• data is not stored on a central server, but only on your computer(s)
• all communication is secured with TLS and perfect forward secrecy ^[archive]
• every node is identified by a strong cryptographic certificate
• a completely open protocol -- open source, open development and open discourse
• portable and simple to use Web GUI

It is possible to tunnel Syncthing traffic over I2P as shown in this guide ^[archive].

To install Syncthing, run.

sudo apt install syncthing

sudo apt install syncthing

Syndie

Syndie ^[archive] is I2P's distributed (decentralized) forum software, allowing asynchronous conversations between anonymous participants. It was the focus of I2P's creator shortly before he ceased public activity. It supports single and multiple author modes, adjustable visibility of posts and post moderation. Syndie features its own minimalist and secure reader to protect against browser exploitation. In 2018, Syndie was being rewritten in another programming language to provide a more modern and simple interface, along with basic image rendering.

A key benefit of Syndie is that unlike centralized forums, it cannot be easily taken offline via denial of service attacks or administrative action, and there is no single point to monitor group activity. Offline forum participation is possible, by 'syncing up' any accumulated changes when it is convenient (days, weeks or even months later). In addition to simple text messages, entire webpages or the full content of sites can be packaged into a single post, which can even be browsed offline.

The Syndie Technical Features section notes:

On the whole, Syndie works at the *content layer* - individual posts are contained in encrypted zip files, and participating in the forum means simply sharing these files. There are no dependencies upon how the files are transferred (over I2P ^[archive], Tor ^[archive], Freenet ^[archive], gnutella ^[archive], bittorrent ^[archive], RSS ^[archive], usenet ^[archive], email ^[archive]), but simple aggregation and distribution tools will be bundled with the standard Syndie release.

To install Syndie, run.

sudo apt install syndie

sudo apt install syndie

ZeroNet

Unfortunately, I2P is not yet natively supported as a tunneling option in ZeroNet. However, progress has been made towards this goal since 2016; see footnotes to follow recent GitHub developments.

Installing I2P on Whonix-Gateway

It is possible to run I2P and Tor simultaneously on Whonix-Gateway ™:

• user → Tor → Internet; and
• user → I2P → Internet

Users who are interested in this configuration should follow the detailed instructions found here ^[archive].

This configuration is untested by Whonix ™ developers and it is considered experimental. Also, Whonix ™ developer HulaHoop has noted it is difficult to have a preconfigured Tor Browser for accessing .i2p domains and other non-clearnet top-level domains, as well as optimizing I2P operations when tunneled over Tor.

For further information and to report successes/failures of this approach, refer to the development discussion ^[archive] and old development discussion ^[archive].

Footnotes

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