Tor vs. I2P and a little Freev&net

There are a great many other applications and projects working on anonymous communication and I2P has been inspired by much of their efforts. This is not a comprehensive list of anonymity resources – both freehaven’s Anonymity Bibliography and GNUnet‘s related projects serve that purpose well. That said, a few systems stand out for further comparison. The following are discussed on this page:

The following are discussed on the other networks page:

The content of this page is subject to update, discussion and dispute, and we welcome comments and additions. You may contribute an analysis by entering a new ticket on

Tor / Onion Routing

[Tor] [Onion Routing]Tor and Onion Routing are both anonymizing proxy networks, allowing people to tunnel out through their low latency mix network. The two primary differences between Tor / Onion-Routing and I2P are again related to differences in the threat model and the out-proxy design (though Tor supports hidden services as well). In addition, Tor takes the directory-based approach – providing a centralized point to manage the overall ‘view’ of the network, as well as gather and report statistics, as opposed to I2P’s distributed network database and peer selection.

The I2P/Tor outproxy functionality does have a few substantial weaknesses against certain attackers – once the communication leaves the mixnet, global passive adversaries can more easily mount traffic analysis. In addition, the outproxies have access to the cleartext of the data transferred in both directions, and outproxies are prone to abuse, along with all of the other security issues we’ve come to know and love with normal Internet traffic.

However, many people don’t need to worry about those situations, as they are outside their threat model. It is, also, outside I2P’s (formal) functional scope (if people want to build outproxy functionality on top of an anonymous communication layer, they can). In fact, some I2P users currently take advantage of Tor to outproxy.

See also the the Tor FAQ for a Tor/I2P comparison from the Tor perspective.

Comparison of Tor and I2P Terminology

While Tor and I2P are similar in many ways, much of the terminology is different.

Tor I2P
Cell Message
Client Router or Client
Circuit Tunnel
Directory NetDb
Directory Server Floodfill Router
Entry Guards Fast Peers
Entry Node Inproxy
Exit Node Outproxy
Hidden Service Eepsite or Destination
Hidden Service Descriptor LeaseSet
Introduction point Inbound Gateway
Node Router
Onion Proxy I2PTunnel Client (more or less)
Relay Router
Rendezvous Point somewhat like Inbound Gateway + Outbound Endpoint
Router Descriptor RouterInfo
Server Router

Benefits of Tor over I2P

  • Much bigger user base; much more visibility in the academic and hacker communities; benefits from formal studies of anonymity, resistance, and performance; has a non-anonymous, visible, university-based leader
  • Has already solved some scaling issues I2P has yet to address
  • Has significant funding
  • Has more developers, including several that are funded
  • More resistant to state-level blocking due to TLS transport layer and bridges (I2P has proposals for “full restricted routes” but these are not yet implemented)
  • Big enough that it has had to adapt to blocking and DOS attempts
  • Designed and optimized for exit traffic, with a large number of exit nodes
  • Better documentation, has formal papers and specifications, better website, many more translations
  • More efficient with memory usage
  • Tor client nodes have very low bandwidth overhead
  • Centralized control reduces the complexity at each node and can efficiently address Sybil attacks
  • A core of high capacity nodes provides higher throughput and lower latency
  • C, not Java (ewww)

Benefits of I2P over Tor

  • Designed and optimized for hidden services, which are much faster than in Tor
  • Fully distributed and self organizing
  • Peers are selected by continuously profiling and ranking performance, rather than trusting claimed capacity
  • Floodfill peers (“directory servers”) are varying and untrusted, rather than hardcoded
  • Small enough that it hasn’t been blocked or DOSed much, or at all
  • Peer-to-peer friendly
  • Packet switched instead of circuit switched
    • implicit transparent load balancing of messages across multiple peers, rather than a single path
    • resilience vs. failures by running multiple tunnels in parallel, plus rotating tunnels
    • scale each client’s connections at O(1) instead of O(N) (Alice has e.g. 2 inbound tunnels that are used by all of the peers Alice is talking with, rather than a circuit for each)
  • Unidirectional tunnels instead of bidirectional circuits, doubling the number of nodes a peer has to compromise to get the same information.
  • Protection against detecting client activity, even when an attacker is participating in the tunnel, as tunnels are used for more than simply passing end to end messages (e.g. netDb, tunnel management, tunnel testing)
  • Tunnels in I2P are short lived, decreasing the number of samples that an attacker can use to mount an active attack with, unlike circuits in Tor, which are typically long lived.
  • I2P APIs are designed specifically for anonymity and security, while SOCKS is designed for functionality.
  • Essentially all peers participate in routing for others
  • The bandwidth overhead of being a full peer is low, while in Tor, while client nodes don’t require much bandwidth, they don’t fully participate in the mixnet.
  • Integrated automatic update mechanism
  • Both TCP and UDP transports
  • Java, not C (ewww)

Other potential benefits of I2P but not yet implemented

…and may never be implemented, so don’t count on them!

  • Defense vs. message count analysis by garlic wrapping multiple messages
  • Defense vs. long term intersection by adding delays at various hops (where the delays are not discernible by other hops)
  • Various mixing strategies at the tunnel level (e.g. create a tunnel that will handle 500 messages / minute, where the endpoint will inject dummy messages if there are insufficient messages, etc)


[Freenet]Freenet is a fully distributed, peer to peer anonymous publishing network, offering secure ways to store data, as well as some approaches attempting to address the loads of a flash flood. While Freenet is designed as a distributed data store, people have built applications on top of it to do more generic anonymous communication, such as static websites and message boards.

Compared to I2P, Freenet offers some substantial benefits – it is a distributed data store, while I2P is not, allowing people to retrieve the content published by others even when the publisher is no longer online. In addition, it should be able to distribute popular data fairly efficiently. I2P itself does not and will not provide this functionality. On the other hand, there is overlap for users who simply want to communicate with each other anonymously through websites, message boards, file sharing programs, etc. There have also been some attempts to develop a distributed data store to run on top of I2P, (most recently a port of Tahoe-LAFS) but nothing is yet ready for general use.

However, even ignoring any implementations issues, there are some concerns about Freenet’s algorithms from both a scalability and anonymity perspective, owing largely to Freenet’s heuristic driven routing. The interactions of various techniques certainly may successfully deter various attacks, and perhaps some aspects of the routing algorithms will provide the hoped for scalability. Unfortunately, not much analysis of the algorithms involved has resulted in positive results, but there is still hope. At the very least, Freenet does provide substantial anonymity against an attacker who does not have the resources necessary to analyze it further.

-Information from

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