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{% block title %}I2P Compared to Tor and Freenet{% endblock %}
{% block content %}<p>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 
<a href="http://freehaven.net/anonbib/topic.html">Anonymity Bibliography</a>
and GNUnet's <a href="https://www.gnunet.org/links/">related projects</a>
serve that purpose well.  That said, a few systems stand out for further
comparison. The following are discussed on this page:</p>
<ul>
<li>Tor / Onion Routing</li>
<li>Freenet</li>
</ul>
<p>The following are discussed on the <a href="othernetworks.html">other networks page:</a></p>
<ul>
<li>Morphmix and Tarzan</li>
<li>Mixminion / Mixmaster</li>
<li>JAP</li>
<li>MUTE / AntsP2P</li>
<li>Haystack</li>
</ul>

<p>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
<a href="http://trac.i2p2.de/report/1">new ticket on trac.i2p2.de</a>.
</p>

<h2>Tor / Onion Routing</h2>
<i><a href="http://www.torproject.org/">[Tor]</a> 
   <a href="http://www.onion-router.net">[Onion Routing]</a></i>
<p>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 <a href="{{ site_url('docs/how/networkdatabase') }}">network 
database</a> and <a href="{{ site_url('docs/how/peerselection') }}">peer selection</a>.</p>

<p>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.</p>

<p>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.</p>
<!--
<p>See also the
<a href="http://wiki.noreply.org/noreply/TheOnionRouter/TorFAQ#ComparisonI2P">the Tor FAQ</a>
for a Tor/I2P comparison from the Tor perspective.</p>
-->

<h3>Comparison of Tor and I2P Terminology</h3>
While Tor and I2P are similar in many ways, much of the terminology is different.
<table>
<tr><th align="left">Tor<th align="left">I2P
<tr><td>Cell<td>Message
<tr><td>Client<td>Router or Client
<tr><td>Circuit<td>Tunnel
<tr><td>Directory<td>NetDb
<tr><td>Directory Server<td>Floodfill Router
<tr><td>Entry Guards<td>Fast Peers
<tr><td>Entry Node<td>Inproxy
<tr><td>Exit Node<td>Outproxy
<tr><td>Hidden Service<td>Eepsite or Destination
<tr><td>Hidden Service Descriptor<td>LeaseSet
<tr><td>Introduction point<td>Inbound Gateway
<tr><td>Node<td>Router
<tr><td>Onion Proxy<td>I2PTunnel Client (more or less)
<tr><td>Relay<td>Router
<tr><td>Rendezvous Point<td>somewhat like Inbound Gateway + Outbound Endpoint
<tr><td>Router Descriptor<td>RouterInfo
<tr><td>Server<td>Router
</table>

<h3>Benefits of Tor over I2P</h3>
<ul>
 <li>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</li>
 <li>Has already solved some scaling issues I2P has yet to address</li>
 <li>Has significant funding</li>
 <li>Has more developers, including several that are funded</li>
 <li>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)</li>
 <li>Big enough that it has had to adapt to blocking and DOS attempts</li>
 <li>Designed and optimized for exit traffic, with a large number of exit nodes</li>
 <li>Better documentation, has formal papers and specifications, better website, many more translations</li>
 <li>More efficient with memory usage</li>
 <li>Tor client nodes have very low bandwidth overhead</li>
 <li>Centralized control reduces the complexity at each
     node and can efficiently address Sybil attacks</li>
 <li>A core of high capacity nodes provides higher
     throughput and lower latency</li>
 <li>C, not Java (ewww)</li>
</ul>

<h3>Benefits of I2P over Tor</h3>
<ul>
 <li>Designed and optimized for hidden services, which are much faster than in Tor</li>
 <li>Fully distributed and self organizing</li>
 <li>Peers are selected by continuously profiling and ranking performance,
     rather than trusting claimed capacity</li>
 <li>Floodfill peers ("directory servers") are varying and untrusted,
     rather than hardcoded</li>
 <li>Small enough that it hasn't been blocked or DOSed much, or at all</li>
 <li>Peer-to-peer friendly</li>
 <li>Packet switched instead of circuit switched
  <ul>
   <li>implicit transparent load balancing of messages 
      across multiple peers, rather than a single path</li>
   <li>resilience vs. failures by running multiple 
       tunnels in parallel, plus rotating tunnels</li>
   <li>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)</li>
  </ul></li>
 <li>Unidirectional tunnels instead of bidirectional
    circuits, doubling the number of nodes a peer has to
    compromise to get the same information.</li>
 <li>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)</li>
 <li>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.</li>
 <li>I2P APIs are designed specifically for anonymity and
     security, while SOCKS is designed for functionality.</li>
 <li>Essentially all peers participate in routing for others</li>
 <li>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.</li>
 <li>Integrated automatic update mechanism</li>
 <li>Both TCP and UDP transports</li>
 <li>Java, not C (ewww)</li>
</ul>

<h3>Other potential benefits of I2P but not yet implemented</h3>
<p>...and may never be implemented, so don't count on them!</p>
<ul>
 <li>Defense vs. message count analysis by garlic wrapping 
     multiple messages</li>
 <li>Defense vs. long term intersection by adding delays 
     at various hops (where the delays are not discernible
     by other hops)</li>
 <li>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)</li>
</ul>


<h2>Freenet</h2>
<i><a href="http://freenetproject.org/">[Freenet]</a></i>

<p>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.</p>

<p>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 <a href="http://tahoe-lafs.org/trac/tahoe-lafs">Tahoe-LAFS</a>)
but nothing is yet ready for general use.</p>

<p>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.</p>

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