113fbc1df3
* Merged in the i2p_0_6_1_10_PRE branch to the trunk, so CVS HEAD is no
longer backwards compatible (and should not be used until 0.6.1.1 is
out)
995 lines
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995 lines
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<head>
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<title>Introducing I2P - a scalable framework for anonymous communication</title>
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<center>
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<b class="title">Introducing I2P</b><br />
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<span class="subtitle">a scalable framework for anonymous communication</span><br />
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<i style="font-size: 8">$Id: techintro.html,v 1.8.2.1 2006/02/13 07:13:35 jrandom Exp $</i>
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<br />
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<br />
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<table border="0" width="50%">
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<tr><td valign="top" align="left">
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<pre>
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* <a href="#intro">Introduction</a>
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* <a href="#op">Operation</a>
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* <a href="#op.overview">Overview</a>
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* <a href="#op.tunnels">Tunnels</a>
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* <a href="#op.netdb">Network Database</a>
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* <a href="#op.transport">Transport protocols</a>
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* <a href="#op.crypto">Cryptography</a>
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</pre>
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</td>
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<td valign="top" align="left">
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<pre>
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* <a href="#future">Future</a>
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* <a href="#future.restricted">Restricted routes</a>
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* <a href="#future.variablelatency">Variable latency</a>
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* <a href="#future.open">Open questions</a>
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</pre>
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</td>
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<td valign="top" align="left">
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<pre>
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* <a href="#similar">Similar systems</a>
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* <a href="#similar.tor">Tor</a>
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* <a href="#similar.freenet">Freenet</a>
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* <a href="#app">Appendix A: Application layer</a>
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</pre>
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</td>
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</tr></table>
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</center>
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<hr />
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<h1 id="intro">Introduction</h1>
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<p>
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I2P is a scalable, self organizing, resilient packet switched anonymous network layer,
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upon which any number of different anonymity or security conscious applications
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can operate. Each of these applications may make their own anonymity, latency, and
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throughput tradeoffs without worrying about the proper implementation of a free
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route mixnet, allowing them to blend their activity with the larger anonymity set of
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users already running on top of I2P. Applications available already provide the full
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range of typical Internet activities - anonymous web browsing, anonymous web hosting,
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anonymous blogging and content syndication (with <a href="#app.syndie">Syndie</a>),
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anonymous chat (via IRC or Jabber), anonymous swarming file transfers (with <a
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href="#app.i2pbt">i2p-bt</a>, <a href="#app.i2psnark">I2PSnark</a>, and
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<a href="#app.azneti2p">Azureus</a>), anonymous file sharing (with
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<a href="#app.i2phex">I2Phex</a>), anonymous email (with <a href="#app.i2pmail">I2Pmail</a>
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and <a href="#app.i2pmail">susimail</a>), anonymous newsgroups, as well as several
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other applications under development. Unlike web sites hosted within content
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distribution networks like <a href="#similar.freenet">Freenet</a> or
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<a href="http://www.ovmj.org/GNUnet/">GNUnet</a>, the services hosted on I2P are fully
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interactive - there are traditional web-style search engines, bulletin boards, blogs
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you can comment on, database driven sites, and bridges to query static systems like
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Freenet without needing to install it locally.
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</p>
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<p>
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With all of these anonymity enabled applications, I2P takes on the role of the message
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oriented middleware - applications say that they want to send some data to a cryptographic
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identifier (a "destination") and I2P takes care of making sure it gets there securely
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and anonymously. I2P also bundles a simple <a href="#app.streaming">streaming</a> library
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to allow I2P's anonymous best-effort messages to transfer as reliable, in-order streams,
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transparently offering a TCP based congestion control algorithm tuned for the high
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bandwidth delay product of the network. While there have been several simple SOCKS
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proxies available to tie existing applications into the network, their value has been
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limited as nearly every application routinely exposes what, in an anonymous context,
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is sensitive information. The only safe way to go is to fully audit an application to
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ensure proper operation, and to assist in that we provide a series of APIs in various
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languages which can be used to make the most out of the network.
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</p>
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<!-- commented out because "The details [...] are " *NOT* " given later" -->
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<!--
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<p>
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The scope of I2P's anonymity protections varies upon the applications running on
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top of them, as well as the choices that each user makes. The aim is to provide
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the options necessary so that a sufficient level of anonymity can be achieved while
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exposing the functionality that people facing up to state level adversaries require.
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At the same time, those facing less powerful adversaries are able to improve their
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throughput and latency while reducing the resources required to provide the necessary
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level of cover. The details of the techniques available for facing adversaries who
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are internal or external, passive or active, local, national, or global, are given
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later.
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</p>
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-->
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<p>
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I2P is not a research project - academic, commercial, or governmental, but is instead
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an engineering effort aimed at doing whatever is necessary to provide a sufficient
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level of anonymity to those who need it. It has been in active development since
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early 2003 with one full time developer and a dedicated group of part time contributors
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from all over the world. All of the work done on I2P is open source and
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freely available on the <a href="http://www.i2p.net/">website</a>, with the majority
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of the code released outright into the public domain, though making use of a few
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cryptographic routines under BSD-style licenses. The people working on I2P do not
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control what people release client applications under, and there are several GPL'ed
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applications available (<a href="#app.i2ptunnel">I2PTunnel</a>,
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<a href="#app.i2pmail">susimail</a>, <a href="#app.i2psnark">I2PSnark</a>, <a href="#app.azneti2p">Azureus</a>,
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<a href="#app.i2phex">I2Phex</a>). <a href="http://www.i2p.net/halloffame">Funding</a>
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for I2P comes entirely from donations, and does not receive any tax breaks in any
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jurisdiction at this time, as many of the developers are themselves anonymous.
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</p>
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<h1 id="op">Operation</h1>
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<h2 id="op.overview">Overview</h2>
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<p>
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To understand I2P's operation, it is essential to understand a few key concepts.
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First, I2P makes a strict separation between the software participating
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in the network (a "router") and the anonymous endpoints ("destinations") associated
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with individual applications. The fact that someone is running I2P is not usually
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a secret. What is hidden is information on what the user is doing, if anything at
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all, as well as what router a particular destination is connected to. End users
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will typically have several local destinations on their router - for instance, one
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proxying in to IRC servers, another supporting the user's anonymous webserver ("eepsite"),
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another for an I2Phex instance, another for torrents, etc.
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</p>
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<p>
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Another critical concept to understand is the "tunnel" - a directed path through
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an explicitly selected set of routers, making use of layered encryption so that
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the messages sent in the tunnel's "gateway" appear entirely random at each hop
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along the path until it reaches the tunnel's "endpoint". These unidirectional
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tunnels can be seen as either "inbound" tunnels or "outbound" tunnels, referring
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to whether they are bringing messages to the tunnel's creator or away from them,
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respectively. The gateway of an inbound tunnel can receive messages from any
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peer and will forward them down through the tunnel until it reaches the (anonymous)
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endpoint (the creator). On the other hand, the gateway of an outbound tunnel is
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the tunnel's creator, and messages sent through that tunnel are encoded so that
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when they reach the outbound tunnel's endpoint, that router has the instructions
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necessary to forward the message on to the appropriate location.
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</p>
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<p>
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A third critical concept to understand is I2P's "network database" (or "netDb")
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- a pair of algorithms used to share network metadata. The two types of metadata
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carried are "routerInfo" and "leaseSets" - the routerInfo gives routers the data
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necessary for contacting a particular router (their public keys, transport
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addresses, etc), while the leaseSet gives routers the information necessary for
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contacting a particular destination. Within each leaseSet, there are any number
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of "leases", each of which specifies the gateway for one of that destination's
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inbound tunnels as well as when that tunnel will expire. The leaseSet also
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contains a pair of public keys which can be used for layered garlic encryption.
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</p>
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<!--
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<p>
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I2P's operation can be understood by putting those three concepts together:
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</p>
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<p><img src="net.png"></p>
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!-->
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<p>
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When Alice wants to send a message to Bob, she first does a lookup in the
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netDb to find Bob's leaseSet, giving her his current inbound tunnel gateways.
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She then picks one of her outbound tunnels and sends the message
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down it with instructions for the outbound tunnel's endpoint to forward the
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message on to one of Bob's inbound tunnel gateways. When the outbound
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tunnel endpoint receives those instructions, it forwards the message as
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requested, and when Bob's inbound tunnel gateway receives it, it is
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forwarded down the tunnel to Bob's router. If Alice wants Bob to be able
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to reply to the message, she needs to transmit her own destination explicitly
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as part of the message itself (taken care of transparently in the
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<a href="#app.streaming">streaming</a> library). Alice may also cut down on
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the response time by bundling her most recent leaseSet with the message so
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that Bob doesn't need to do a netDb lookup for it when he wants to reply, but this
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is optional.
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</p>
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<p>
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While the tunnels themselves have layered encryption to prevent unauthorized
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disclosure to peers inside the network (as the transport layer itself does to
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prevent unauthorized disclosure to peers outside the network), it is necessary
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to add an additional end to end layer of encryption to hide the message from the
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outbound tunnel endpoint and the inbound tunnel gateway. This
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"<a href="#op.garlic">garlic encryption</a>" lets Alice's router wrap up multiple
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messages into a single "garlic message", encrypted to a particular public key
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so that intermediary peers cannot determine either how many messages are within
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the garlic, what those messages say, or where those individual cloves are
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destined. For typical end to end communication between Alice and Bob, the
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garlic will be encrypted to the public key published in Bob's leaseSet,
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allowing the message to be encrypted without giving out the public key to Bob's
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own router.
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</p>
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<p>
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Another important fact to keep in mind is that I2P is entirely message based
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and that some messages may be lost along the way. Applications using I2P
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can use the message oriented interfaces and take care of their own congestion
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control and reliability needs, but most would be best served by reusing the
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provided <a href="#app.streaming">streaming</a> library to view I2P as a streams
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based network.
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</p>
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<h2 id="op.tunnels">Tunnels</h2>
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<p>
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Both inbound and outbound tunnels work along similar principles - the tunnel
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gateway accumulates a number of tunnel messages, eventually preprocessing them
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into something for tunnel delivery. Next, the gateway encrypts that preprocessed
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data and forwards it to the first hop. That peer and subsequent tunnel
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participants add on a layer of encryption after verifying that it isn't a
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duplicate before forward it on to the next peer. Eventually, the
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message arrives at the endpoint where the messages are split out again and
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forwarded on as requested. The difference arises in what
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the tunnel's creator does - for inbound tunnels, the creator is the endpoint
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and they simply decrypt all of the layers added, while for outbound tunnels,
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the creator is the gateway and they pre-decrypt all of the layers so that after
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all of the layers of per-hop encryption are added, the message arrives in the
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clear at the tunnel endpoint.
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</p>
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<p>
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The choice of specific peers to pass on messages as well as their particular
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ordering is important to understanding both I2P's anonymity and performance
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characteristics. While the network database (below) has its own criteria for
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picking what peers to query and store entries on, tunnels may use any peers in
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the network in any order (and even any number of times) in a single tunnel. If
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perfect latency and capacity data were globally known, selection and ordering
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would be driven by the particular needs of the client in tandem with their threat
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model. Unfortunately, latency and capacity data is not trivial to gather
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anonymously, and depending upon untrusted peers to provide this information has
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its own serious anonymity implications.
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</p>
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<p>
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From an anonymity perspective, the simplest technique would be to pick peers
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randomly from the entire network, order them randomly, and use those peers
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in that order for all eternity. From a performance perspective, the simplest
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technique would be to pick the fastest peers with the necessary spare capacity,
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spreading the load across different peers to handle transparent failover, and
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to rebuild the tunnel whenever capacity information changes. While the former
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is both brittle and inefficient, the later requires inaccessible information
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and offers insufficient anonymity. I2P is instead working on offering a range
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of peer selection strategies, coupled with anonymity aware measurement code to
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organize the peers by their profiles.
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</p>
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<p>
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As a base, I2P is constantly profiling the peers with which it interacts with
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by measuring their indirect behavior - for instance, when a peer responds to
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a netDb lookup in 1.3 seconds, that round trip latency is recorded in the
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profiles for all of the routers involved in the two tunnels (inbound and
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outbound) through which the request and response passed, as well as the queried
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peer's profile. Direct measurement, such as transport layer latency or
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congestion, is not used as part of the profile, as it can be manipulated and
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associated with the measuring router, exposing them to trivial attacks. While
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gathering these profiles, a series of calculations are run on each to summarize
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its performance - its latency, capacity to handle lots of activity, whether they
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are currently overloaded, and how well integrated into the network they seem to
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be. These calculations are then compared for active peers to organize the routers
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into four tiers - fast and high capacity, high capacity, not failing, and failing.
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The thresholds for those tiers are determined dynamically, and while they
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currently use fairly simple algorithms, alternatives exist.
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</p>
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<p>
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Using this profile data, the simplest reasonable peer selection strategy is to
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pick peers randomly from the top tier (fast and high capacity), and this is
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currently deployed for client tunnels. Exploratory tunnels (used for netDb
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and tunnel management) pick peers randomly from the not failing tier (which
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includes routers in 'better' tiers as well), allowing the peer to sample
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routers more widely, in effect optimizing the peer selection through randomized
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hill climbing. These strategies alone do however leak information regarding the
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peers in the router's tip tier through predecessor and netDb harvesting attacks.
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In turn, several alternatives exist which, while not balancing the load as evenly,
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will address the attacks mounted by particular classes of adversaries.
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</p>
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<p>
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By picking a random key and ordering the peers according to their XOR distance
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from it, the information leaked is reduced in predecessor and harvesting attacks
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according to the peers' failure rate and the tier's churn. Another simple strategy
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for dealing with netDb harvesting attacks is to simply fix the inbound tunnel
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gateway(s) yet randomize the peers further on in the tunnels. To deal with
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predecessor attacks for adversaries which the client contacts, the outbound tunnel
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endpoints would also remain fixed. The selection of which peer to fix on the most
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exposed point would of course need to have a limit to the duration, as all peers
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fail eventually, so it could either be reactively adjusted or proactively avoided
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to mimic a measured mean time between failures of other routers. These two strategies
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can in turn be combined, using a fixed exposed peer and an XOR based ordering within
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the tunnels themselves. A more rigid strategy would fix the exact peers and ordering
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of a potential tunnel, only using individual peers if all of them agree to participate
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in the same way each time. This varies from the XOR based ordering in that the
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predecessor and successor of each peer is always the same, while the XOR only makes
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sure their order doesn't change.
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</p>
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<p>
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As mentioned before, I2P currently (release 0.6.1.1) includes the tiered random
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strategy above, but the others are planned for the 0.6.2 release. A more detailed
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discussion of the mechanics involved in tunnel operation, management, and peer
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selection can be found in the
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<a href="http://dev.i2p.net/cgi-bin/cvsweb.cgi/i2p/router/doc/tunnel-alt.html?rev=HEAD">tunnel spec</a>.
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</p>
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<h2 id="op.netdb">Network Database</h2>
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<p>
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As mentioned earlier, I2P's netDb works to share the network's metadata. Two
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algorithms are used to accomplish this - primarily, a small set of routers are
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designated as "floodfill peers", while the rest of the routers participate in
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the <a href="http://en.wikipedia.org/wiki/Kademlia">Kademlia </a> derived
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distributed hash table for redundancy. To integrate the two algorithms, each
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router always uses the Kademlia style store and fetch, but acts as if the
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floodfill peers are 'closest' to the key in question. Additionally, when a
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peer publishes a key into the netDb, after a brief delay they query another
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random floodfill peer, asking them for the key, and if that peer does not have
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it, they move on and republish the key again. Behind the scenes, when one of
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the floodfill peers receives a new valid key, they republish it to the other
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floodfill peers who then cache it locally.
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</p>
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<p>
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Each piece of data in the netDb is self authenticating - signed by the
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appropriate party and verified by anyone who uses or stores it. In addition,
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the data has liveliness information within it, allowing irrelevant entries to be
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dropped, newer entries to replace older ones, and, for the paranoid, protection
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against certain classes of attack. This is also why I2P bundles the necessary
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code for maintaining the correct time, occasionally querying some SNTP servers
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(the <a href="http://www.pool.ntp.org/">pool.ntp.org</a> round robin by default)
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and detecting skew between routers at the transport layer.
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</p>
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<p>
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The routerInfo structure itself contains all of the information that one router
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needs to know to securely send messages to another router. This includes their
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identity (made up of a 2048bit ElGamal public key, a 1024bit DSA public key, and
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a certificate), the transport addresses which they can be reached on, such as
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an IP address and port, when the structure was published, and a set of arbitrary
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uninterpreted text options. In addition, there is a signature against all of
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that data as generated by the included DSA public key. The key for this routerInfo
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structure in the netDb is the SHA256 hash of the router's identity. The options
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published are often filled with information helpful in debugging I2P's operation,
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but when I2P reaches the 1.0 release, the options will be disabled and kept blank.
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</p>
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<p>
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The leaseSet structure is similar, in that it includes the I2P destination
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(comprised of a 2048bit ElGamal public key, a 1024bit DSA public key, and a
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certificate), a list of "leases", and a pair of public keys for garlic encrypting
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messages to the destination. Each of the leases specify one of the destination's
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inbound tunnel gateways by including the SHA256 of the gateway's identity, a 4
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byte tunnel id on that gateway, and when that tunnel will expire. The key for
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the leaseSet in the netDb is the SHA256 of the destination itself.
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</p>
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<p>
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As the router currently automatically bundles the leaseSet for the sender inside
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a garlic message to the recipient, the leaseSet for destinations which will not
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receive unsolicited messages do not need to be published in the netDb at all. If
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the destination itself is sensitive, the leaseSet could instead be transmitted
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through other means without ever going into the netDb.
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</p>
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<p>
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Bootstrapping the netDb itself is simple - once a router has at least one routerInfo
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of a reachable peer, they query that router for references to other routers in the
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network with the Kademlia healing algorithm. Each routerInfo reference is stored in
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an individual file in the router's netDb subdirectory, allowing people to easily
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share their references to bootstrap new users.
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</p>
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<p>
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Unlike traditional DHTs, the very act of conducting a search distributes the data
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as well, since rather passing Kademlia's standard IP+port pairs, references are given
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to the routers that the peer should query next (namely, the SHA256 of those routers'
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identities). As such, iteratively searching for a particular destination's leaseSet
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or router's routerInfo will also provide you with the routerInfo of the peers along
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the way. In addition, due to the time sensitivity of the data published, the information
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doesn't often need to migrate between peers - since a tunnel is only valid for 10
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minutes, the leaseSet can be dropped after that time has passed. To take into
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account Sybil attacks on the netDb, the Kademlia routing location used for any given
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|
key varies over time. For instance, rather than storing a routerInfo on the peers
|
|
closest to SHA256(routerInfo.identity), they are stored on the peers closest to
|
|
SHA256(routerInfo.identity + YYYYMMDD), requiring an adversary to remount the attack
|
|
again daily so as to maintain their closeness to the current routing key. As the
|
|
very fact that a router is making a lookup for a given key may expose sensitive data
|
|
(and the fact that a router is <i>publishing</i> a given key even more so), all netDb
|
|
messages are transmitted through the router's exploratory tunnels.
|
|
</p>
|
|
|
|
<p>
|
|
The netDb plays a very specific role in the I2P network, and the algorithms have
|
|
been tuned towards our needs. This also means that it hasn't been tuned to address the
|
|
needs we have yet to run into. As the network grows, the primary floodfill algorithm
|
|
will need to be refined to exploit the capacity available, or perhaps replaced with
|
|
another technique for securely distributing the network metadata.
|
|
</p>
|
|
|
|
<h2 id="op.transport">Transport protocols</h2>
|
|
|
|
<p>
|
|
Communication between routers needs to provide confidentiality and integrity
|
|
against external adversaries while authenticating that the router contacted
|
|
is the one who should receive a given message. The particulars of how routers
|
|
communicate with other routers aren't critical - three separate protocols have
|
|
been used at different points to provide those bare necessities. To accommodate
|
|
the need for high degree communication (as a number of routers will end up
|
|
speaking with many others), I2P moved from a TCP based transport
|
|
to a UDP based one - "Secure Semireliable UDP", or "SSU". As described in the
|
|
<a href="http://dev.i2p.net/cgi-bin/cvsweb.cgi/i2p/router/doc/udp.html?rev=HEAD">SSU spec</a>:</p>
|
|
|
|
<blockquote>
|
|
The goal of this protocol is to provide secure, authenticated,
|
|
semireliable, and unordered message delivery, exposing only a minimal amount of
|
|
data easily discernible to third parties. It should support high degree
|
|
communication as well as TCP-friendly congestion control, and may include
|
|
PMTU detection. It should be capable of efficiently moving bulk data at rates
|
|
sufficient for home users. In addition, it should support techniques for
|
|
addressing network obstacles, like most NATs or firewalls.
|
|
</blockquote>
|
|
|
|
<h2 id="op.crypto">Cryptography</h2>
|
|
|
|
<p>
|
|
A bare minimum set of cryptographic primitives are combined together to provide I2P's
|
|
layered defenses against a variety of adversaries. At the lowest level, interrouter
|
|
communication is protected by the transport layer security - SSU
|
|
encrypts each packet with AES256/CBC with both an explicit IV and MAC (HMAC-MD5-128)
|
|
after agreeing upon an ephemeral session key through a 2048bit Diffie-Hellman exchange,
|
|
station-to-station authentication with the other router's DSA key, plus each network
|
|
message has their own hash for local integrity checking.
|
|
<a href="#op.tunnels">Tunnel</a> messages passed over the transports have their own
|
|
layered AES256/CBC encryption with an explicit IV and verified at the tunnel endpoint
|
|
with an additional SHA256 hash. Various other messages are passed along inside
|
|
"garlic messages", which are encrypted with ElGamal/AES+SessionTags (explained below).
|
|
</p>
|
|
|
|
<h3 id="op.garlic">Garlic messages</h3>
|
|
|
|
<p>
|
|
Garlic messages are an extension of "onion" layered encryption, allowing the contents
|
|
of a single message to contain multiple "cloves" - fully formed messages alongside
|
|
their own instructions for delivery. Messages are wrapped into a garlic message whenever
|
|
the message would otherwise be passing in cleartext through a peer who should not have
|
|
access to the information - for instance, when a router wants to ask another router to
|
|
participate in a tunnel, they wrap the request inside a garlic, encrypt that garlic to
|
|
the receiving router's 2048bit ElGamal public key, and forward it through a tunnel.
|
|
Another example is when a client wants to send a message to a destination - the sender's
|
|
router will wrap up that data message (alongside some other messages) into a garlic,
|
|
encrypt that garlic to the 2048bit ElGamal public key published in the recipient's
|
|
leaseSet, and forward it through the appropriate tunnels.
|
|
</p>
|
|
|
|
<p>
|
|
The "instructions" attached to each clove inside the encryption layer includes the
|
|
ability to request that the clove be forwarded locally, to a remote router, or to a
|
|
remote tunnel on a remote router. There are fields in those instructions allowing a
|
|
peer to request that the delivery be delayed until a certain time or condition has
|
|
been met, though they won't be honored until the
|
|
<a href="#future.variablelatency">nontrivial delays</a> are deployed. It is possible to
|
|
explicitly route garlic messages any number of hops without building tunnels, or even
|
|
to reroute tunnel messages by wrapping them in garlic messages and forwarding them a
|
|
number of hops prior to delivering them to the next hop in the tunnel, but those
|
|
techniques are not currently used in the existing implementation.
|
|
</p>
|
|
|
|
<h3 id="op.sessiontags">Session tags</h3>
|
|
|
|
<p>
|
|
As an unreliable, unordered, message based system, I2P uses a simple combination of
|
|
asymmetric and symmetric encryption algorithms to provide data confidentiality and
|
|
integrity to garlic messages. As a whole, the combination is referred to as
|
|
ElGamal/AES+SessionTags, but that is an excessively verbose way to describe the simple
|
|
use of 2048bit ElGamal, AES256, SHA256, and 32 byte nonces.
|
|
</p>
|
|
|
|
<p>
|
|
The first time a router wants to encrypt a garlic message to another router, they encrypt
|
|
the keying material for an AES256 session key with ElGamal and append the AES256/CBC
|
|
encrypted payload after that encrypted ElGamal block. In addition to the encrypted
|
|
payload, the AES encrypted section contains the payload length, the SHA256 hash of the
|
|
unencrypted payload, as well as a number of "session tags" - random 32 byte nonces. The
|
|
next time the sender wants to encrypt a garlic message to another router, rather than
|
|
ElGamal encrypt a new session key they simply pick one of the previously delivered session
|
|
tags and AES encrypt the payload like before, using the session key used with that
|
|
session tag, prepended with the session tag itself. When a router receives a garlic encrypted
|
|
message, they check the first 32 bytes to see if it matches an available session tag - if
|
|
it does, they simply AES decrypt the message, but if it does not, they ElGamal decrypt the
|
|
first block.
|
|
</p>
|
|
|
|
<p>
|
|
Each session tag can be used only once so as to prevent internal adversaries from unnecessarily
|
|
correlating different messages as being between the same routers. The sender of an
|
|
ElGamal/AES+SessionTag encrypted message chooses when and how many tags to deliver,
|
|
prestocking the recipient with enough tags to cover a volley of messages. Garlic messages
|
|
may detect the successful tag delivery by bundling a small additional message as a clove (a
|
|
"delivery status message") - when the garlic message arrives at the intended recipient and
|
|
is decrypted successfully, this small delivery status message is one of the cloves exposed and
|
|
has instructions for the recipient to send the clove back to the original sender (through an
|
|
inbound tunnel, of course). When the original sender receives this delivery status message,
|
|
they know that the session tags bundled in the garlic message were successfully delivered.
|
|
</p>
|
|
|
|
<p>
|
|
Session tags themselves have a very short lifetime, after which they are discarded
|
|
if not used. In addition, the quantity stored for each key is limited, as are the
|
|
number of keys themselves - if too many arrive, either new or old messages may be
|
|
dropped. The sender keeps track whether messages using session tags are getting
|
|
through, and if there isn't sufficient communication it may drop the ones previously
|
|
assumed to be properly delivered, reverting back to the full expensive ElGamal
|
|
encryption.
|
|
</p>
|
|
|
|
<p>
|
|
One alternative is to transmit only a single session tag, and from that, seed a
|
|
deterministic PRNG for determining what tags to use or expect. By keeping this
|
|
PRNG roughly synchronized between the sender and recipient (the recipient precomputes a
|
|
window of the next e.g. 50 tags), the overhead of periodically bundling a large number
|
|
of tags is removed, allowing more options in the space/time tradeoff, and perhaps
|
|
reducing the number of ElGamal encryptions necessary. However, it would depend
|
|
upon the strength of the PRNG to provide the necessary cover against internal
|
|
adversaries, though perhaps by limiting the amount of times each PRNG is used, any
|
|
weaknesses can be minimized. At the moment, there are no immediate plans to move
|
|
towards these synchronized PRNGs.
|
|
</p>
|
|
|
|
<h1 id="future">Future</h1>
|
|
<p>
|
|
While I2P is currently functional and sufficient for many scenarios, there are
|
|
several areas which require further improvement to meet the needs of those
|
|
facing more powerful adversaries as well as substantial user experience optimization.
|
|
</p>
|
|
|
|
<h2 id="future.restricted">Restricted route operation</h2>
|
|
|
|
<p>
|
|
I2P is an overlay network designed to be run on top of a functional packet switched
|
|
network, exploiting the end to end principle to offer anonymity and security.
|
|
While the Internet no longer fully embraces the end to end principle, I2P does require a
|
|
substantial portion of the network to be reachable - there may be a number of peers
|
|
along the edges running using restricted routes, but I2P does not include an
|
|
appropriate routing algorithm for the degenerate case where most peers are
|
|
unreachable. It would, however work on top of a network employing such an
|
|
algorithm.
|
|
</p>
|
|
|
|
<p>
|
|
Restricted route operation, where there are limits to what peers are
|
|
reachable directly, has several different functional and anonymity
|
|
implications, dependent upon how the restricted routes are handled. At the most
|
|
basic level, restricted routes exist when a peer is behind a NAT or firewall which
|
|
does not allow inbound connections. This was largely addressed in I2P 0.6.0.6 by
|
|
integrating distributed hole punching into the transport layer, allowing people
|
|
behind most NATs and firewalls to receive unsolicited connections without any
|
|
configuration. However, this does not limit the exposure of the peer's IP address to
|
|
routers inside the network, as they can simply get introduced to the peer through
|
|
the published introducer.
|
|
</p>
|
|
|
|
<p>
|
|
Beyond the functional handling of restricted routes, there are two levels of
|
|
restricted operation that can be used to limit the exposure of one's IP address -
|
|
using router-specific tunnels for communication, and offering 'client routers'. For
|
|
the former, routers can either build a new pool of tunnels or reuse their exploratory
|
|
pool, publishing the inbound gateways to some of them as part of their routerInfo in
|
|
place of their transport addresses. When a peer wants to get in touch with them,
|
|
they see those tunnel gateways in the netDb and simply send the relevant message to
|
|
them through one of the published tunnels. If the peer behind the restricted route
|
|
wants to reply, it may do so either directly (if they are willing to expose their IP
|
|
to the peer) or indirectly through their outbound tunnels. When the routers that the
|
|
peer has direct connections to want to reach it (to forward tunnel messages, for
|
|
instance), they simply prioritize their direct connection over the published tunnel
|
|
gateway. The concept of 'client routers' simply extends the restricted route by not
|
|
publishing any router addresses. Such a router would not even need to publish their
|
|
routerInfo in the netDb, merely providing their self signed routerInfo to the peers
|
|
that it contacts (necessary to pass the router's public keys). Both levels of
|
|
restricted route operation are planned for I2P 2.0.
|
|
</p>
|
|
|
|
<p>
|
|
There are tradeoffs for those behind restricted routes, as they would likely
|
|
participate in other people's tunnels less frequently, and the routers which
|
|
they are connected to would be able to infer traffic patterns that would not
|
|
otherwise be exposed. On the other hand, if the cost of that exposure is less
|
|
than the cost of an IP being made available, it may be worthwhile. This, of course,
|
|
assumes that the peers that the router behind a restricted route contacts are not
|
|
hostile - either the network is large enough that the probability of using a hostile
|
|
peer to get connected is small enough, or trusted (and perhaps temporary) peers are
|
|
used instead.
|
|
</p>
|
|
|
|
<h2 id="future.variablelatency">Variable latency</h2>
|
|
|
|
<p>
|
|
Even though the bulk of I2P's initial efforts have been on low latency communication,
|
|
it was designed with variable latency services in mind from the beginning. At the
|
|
most basic level, applications running on top of I2P can offer the anonymity of
|
|
medium and high latency communication while still blending their traffic patterns
|
|
in with low latency traffic. Internally though, I2P can offer its own medium and
|
|
high latency communication through the garlic encryption - specifying that the
|
|
message should be sent after a certain delay, at a certain time, after a certain
|
|
number of messages have passed, or another mix strategy. With the layered encryption,
|
|
only the router that the clove exposed the delay request would know that the message
|
|
requires high latency, allowing the traffic to blend in further with the low latency
|
|
traffic. Once the transmission precondition is met, the router holding on to the
|
|
clove (which itself would likely be a garlic message) simply forwards it as
|
|
requested - to a router, to a tunnel, or, most likely, to a remote client destination.
|
|
</p>
|
|
|
|
<p>
|
|
There are a substantial number of ways to exploit this capacity for high latency
|
|
comm in I2P, but for the moment, doing so has been scheduled for the I2P 3.0 release.
|
|
In the meantime, those requiring the anonymity that high latency comm can offer should
|
|
look towards the application layer to provide it.
|
|
</p>
|
|
|
|
<h2 id="future.open">Open questions</h2>
|
|
<pre>
|
|
How to get rid of the timing constraint?
|
|
Can we deal with the sessionTags more efficiently?
|
|
What, if any, batching/mixing strategies should be made available on the tunnels?
|
|
What other tunnel peer selection and ordering strategies should be available?
|
|
</pre>
|
|
|
|
<h1 id="similar">Similar systems</h1>
|
|
<p>
|
|
I2P's architecture builds on the concepts of message oriented middleware, the topology
|
|
of DHTs, the anonymity and cryptography of free route mixnets, and the adaptability of
|
|
packet switched networking. The value comes not from novel concepts of algorithms
|
|
though, but from careful engineering combining the research results of existing
|
|
systems and papers. While there are a few similar efforts worth reviewing, both for
|
|
technical and functional comparisons, two in particular are pulled out here - Tor
|
|
and Freenet.
|
|
</p>
|
|
|
|
<h2 id="similar.tor">Tor</h2>
|
|
<p><i><a href="http://tor.eff.org/">website</a></i></p>
|
|
|
|
<p>
|
|
At first glance, Tor and I2P have many functional and anonymity related similarities.
|
|
While I2P's development began before we were aware of the early stage efforts on Tor,
|
|
many of the lessons of the original onion routing and ZKS efforts were integrated into
|
|
I2P's design. Rather than building an essentially trusted, centralized system with
|
|
directory servers, I2P has a self organizing network database with each peer taking on
|
|
the responsibility of profiling other routers to determine how best to exploit available
|
|
resources. Another key difference is that while both I2P and Tor use layered and
|
|
ordered paths (tunnels and circuits/streams), I2P is fundamentally a packet switched
|
|
network, while Tor is fundamentally a circuit switched one, allowing I2P to
|
|
transparently route around congestion or other network failures, operate redundant
|
|
pathways, and load balance the data across available resources. While Tor offers
|
|
the useful outproxy functionality by offering integrated outproxy discovery and
|
|
selection, I2P leaves such application layer decisions up to applications running on
|
|
top of I2P - in fact, I2P has even externalized the TCP-like streaming library itself
|
|
to the application layer, allowing developers to experiment with different strategies,
|
|
exploiting their domain specific knowledge to offer better performance.
|
|
</p>
|
|
|
|
<p>
|
|
From an anonymity perspective, there is much similarity when the core networks are
|
|
compared. However, there are a few key differences. When dealing with an internal
|
|
adversary or most external adversaries, I2P's simplex tunnels expose half as much
|
|
traffic data than would be exposed with Tor's duplex circuits by simply looking at
|
|
the flows themselves - an HTTP request and response would follow the same path in
|
|
Tor, while in I2P the packets making up the request would go out through one or
|
|
more outbound tunnels and the packets making up the response would come back through
|
|
one or more different inbound tunnels. While I2P's peer selection and ordering
|
|
strategies should sufficiently address predecessor attacks, I2P can trivially
|
|
mimic Tor's non-redundant duplex tunnels by simply building an inbound and
|
|
outbound tunnel along the same routers.</p>
|
|
|
|
<p>
|
|
Another anonymity issue comes up in Tor's use of telescopic tunnel creation, as
|
|
simple packet counting and timing measurements as the cells in a circuit pass
|
|
through an adversary's node exposes statistical information regarding where the
|
|
adversary is within the circuit. I2P's unidirectional tunnel creation with a
|
|
single message so that this data is not exposed. Protecting the position in a
|
|
tunnel is important, as an adversary would otherwise be able to mounting a
|
|
series of powerful predecessor, intersection, and traffic confirmation attacks.
|
|
</p>
|
|
|
|
<p>
|
|
Tor's support for a second tier of "onion proxies" does offer a nontrivial degree
|
|
of anonymity while requiring a low cost of entry, while I2P will not offer this
|
|
topology until <a href="#future.restricted">2.0</a>.
|
|
</p>
|
|
|
|
<p>
|
|
On the whole, Tor and I2P complement each other in their focus - Tor works towards
|
|
offering high speed anonymous Internet outproxying, while I2P works towards offering
|
|
a decentralized resilient network in itself. In theory, both can be used to achieve
|
|
both purposes, but given limited development resources, they both have their
|
|
strengths and weaknesses. The I2P developers have considered the steps necessary to
|
|
modify Tor to take advantage of I2P's design, but concerns of Tor's viability under
|
|
resource scarcity suggest that I2P's packet switching architecture will be able to
|
|
exploit scarce resources more effectively.
|
|
</p>
|
|
|
|
<h2 id="similar.freenet">Freenet</h2>
|
|
<p><i><a href="http://www.freenetproject.org/">website</a></i></p>
|
|
|
|
<p>
|
|
Freenet played a large part in the initial stages of I2P's design - giving proof to
|
|
the viability of a vibrant pseudonymous community completely contained within the
|
|
network, demonstrating that the dangers inherent in outproxies could be avoided.
|
|
The first seed of I2P began as a replacement communication layer for Freenet,
|
|
attempting to factor out the complexities of a scalable, anonymous and secure point
|
|
to point communication from the complexities of a censorship resistant distributed
|
|
data store. Over time however, some of the anonymity and scalability issues
|
|
inherent in Freenet's algorithms made it clear that I2P's focus should stay strictly
|
|
on providing a generic anonymous communication layer, rather than as a component of
|
|
Freenet. Over the years, the Freenet developers have come to see the weaknesses
|
|
in the older design, prompting them to suggest that they will require a "premix"
|
|
layer to offer substantial anonymity. In other words, Freenet needs to run on top
|
|
of a mixnet such as I2P or Tor, with "client nodes" requesting and publishing data
|
|
through the mixnet to the "server nodes" which then fetch and store the data according
|
|
to Freenet's heuristic distributed data storage algorithms.
|
|
</p>
|
|
|
|
<p>
|
|
Freenet's functionality is very complementary to I2P's, as Freenet natively provides
|
|
many of the tools for operating medium and high latency systems, while I2P natively
|
|
provides the low latency mix network suitable for offering adequate anonymity. The
|
|
logic of separating the mixnet from the censorship resistant distributed data store
|
|
still seems self evident from an engineering, anonymity, security, and resource
|
|
allocation perspective, so hopefully the Freenet team will pursue efforts in that
|
|
direction, if not simply reusing (or helping to improve, as necessary) existing
|
|
mixnets like I2P or Tor.
|
|
</p>
|
|
|
|
<p>
|
|
It is worth mentioning that there has recently been discussion and work by the
|
|
Freenet developers on a "globally scalable darknet" using restricted routes between
|
|
peers of various trust. While insufficient information has been made publicly
|
|
available regarding how such a system would operate for a full review, from what
|
|
has been said the anonymity and scalability claims seem highly dubious. In
|
|
particular, the appropriateness for use in hostile regimes against state level
|
|
adversaries has been tremendously overstated, and any analysis on the implications
|
|
of resource scarcity upon the scalability of the network has seemingly been avoided.
|
|
Further questions regarding susceptibility to traffic analysis, trust, and other topics
|
|
do exist, but a more in-depth review of this "globally scalable darknet" will have
|
|
to wait until the Freenet team makes more information available.
|
|
</p>
|
|
|
|
<h1 id="app">Appendix A: Application layer</h1>
|
|
|
|
<p>
|
|
I2P itself doesn't really do much - it simply sends messages to remote destinations
|
|
and receives messages targeting local destinations - most of the interesting work
|
|
goes on at the layers above it. By itself, I2P could be seen as an anonymous and
|
|
secure IP layer, and the bundled <a href="#app.streaming">streaming library</a> as
|
|
an implementation of an anonymous and secure TCP layer on top of it. Beyond that,
|
|
<a href="#app.i2ptunnel">I2PTunnel</a> exposes a generic TCP proxying system for
|
|
either getting into or out of the I2P network, plus a variety of network
|
|
applications provide further functionality for end users.
|
|
</p>
|
|
|
|
<h2 id="app.streaming">Streaming library</h2>
|
|
|
|
<p>
|
|
The streaming library has grown organically for I2P - first mihi implemented the
|
|
"mini streaming library" as part of I2PTunnel, which was limited to a window
|
|
size of 1 message (requiring an ACK before sending the next one), and then it was
|
|
refactored out into a generic streaming interface (mirroring TCP sockets) and the
|
|
full streaming implementation was deployed with a sliding window protocol and
|
|
optimizations to take into account the high bandwidth x delay product. Individual
|
|
streams may adjust the maximum packet size and other options, though the default
|
|
of 4KB compressed seems a reasonable tradeoff between the bandwidth costs of
|
|
retransmitting lost messages and the latency of multiple messages.
|
|
</p>
|
|
|
|
<p>
|
|
In addition, in consideration of the relatively high cost of subsequent messages,
|
|
the streaming library's protocol for scheduling and delivering messages has been optimized to
|
|
allow individual messages passed to contain as much information as is available.
|
|
For instance, a small HTTP transaction proxied through the streaming library can
|
|
be completed in a single round trip - the first message bundles a SYN, FIN, and
|
|
the small payload (an HTTP request typically fits) and the reply bundles the SYN,
|
|
FIN, ACK, and the small payload (many HTTP responses fit). While an additional
|
|
ACK must be transmitted to tell the HTTP server that the SYN/FIN/ACK has been
|
|
received, the local HTTP proxy can deliver the full response to the browser
|
|
immediately.
|
|
</p>
|
|
|
|
<p>
|
|
On the whole, however, the streaming library bears much resemblance to an
|
|
abstraction of TCP, with its sliding windows, congestion control algorithms
|
|
(both slow start and congestion avoidance), and general packet behavior (ACK,
|
|
SYN, FIN, RST, rto calculation, etc).
|
|
</p>
|
|
|
|
<h2 id="app.naming">Naming library and addressbook</h2>
|
|
<p><i>Developed by: mihi, Ragnarok</i></p>
|
|
|
|
<p>
|
|
Naming within I2P has been an oft-debated topic since the very beginning with
|
|
advocates across the spectrum of possibilities. However, given I2P's inherent
|
|
demand for secure communication and decentralized operation, the traditional
|
|
DNS-style naming system is clearly out, as are "majority rules" voting systems.
|
|
Instead, I2P ships with a generic naming library and a base implementation
|
|
designed to work off a local name to destination mapping, as well as an optional
|
|
add-on application called the "addressbook". The addressbook is a web-of-trust
|
|
driven secure, distributed, and human readable naming system, sacrificing only
|
|
the call for all human readable names to be globally unique by mandating only
|
|
local uniqueness. While all messages in I2P are cryptographically addressed
|
|
by their destination, different people can have local addressbook entries for
|
|
"Alice" which refer to different destinations. People can still discover new
|
|
names by importing published addressbooks of peers specified in their web of trust,
|
|
by adding in the entries provided through a third party, or (if some people organize
|
|
a series of published addressbooks using a first come first serve registration
|
|
system) people can choose to treat these addressbooks as name servers, emulating
|
|
traditional DNS.
|
|
</p>
|
|
|
|
<p>
|
|
I2P does not promote the use of DNS-like services though, as the damage done
|
|
by hijacking a site can be tremendous - and insecure destinations have no
|
|
value. DNSsec itself still falls back on registrars and certificate authorities,
|
|
while with I2P, requests sent to a destination cannot be intercepted or the reply
|
|
spoofed, as they are encrypted to the destination's public keys, and a destination
|
|
itself is just a pair of public keys and a certificate. DNS-style systems on the
|
|
other hand allow any of the name servers on the lookup path to mount simple denial
|
|
of service and spoofing attacks. Adding on a certificate authenticating the
|
|
responses as signed by some centralized certificate authority would address many of
|
|
the hostile nameserver issues but would leave open replay attacks as well as
|
|
hostile certificate authority attacks.
|
|
</p>
|
|
|
|
<p>
|
|
Voting style naming is dangerous as well, especially given the effectiveness of
|
|
Sybil attacks in anonymous systems - the attacker can simply create an arbitrarily
|
|
high number of peers and "vote" with each to take over a given name. Proof-of-work
|
|
methods can be used to make identity non-free, but as the network grows the load
|
|
required to contact everyone to conduct online voting is implausible, or if the
|
|
full network is not queried, different sets of answers may be reachable.
|
|
</p>
|
|
|
|
<p>
|
|
As with the Internet however, I2P is keeping the design and operation of a
|
|
naming system out of the (IP-like) communication layer. The bundled naming library
|
|
includes a simple service provider interface which alternate naming systems can
|
|
plug into, allowing end users to drive what sort of naming tradeoffs they prefer.
|
|
</p>
|
|
|
|
<h2 id="app.syndie">Syndie</h2>
|
|
|
|
<p>
|
|
Syndie is a safe, anonymous blogging / content publication / content aggregation system.
|
|
It lets you create information, share it with others, and read posts from those you're
|
|
interested in, all while taking into consideration your needs for security and anonymity.
|
|
Rather than building its own content distribution network, Syndie is designed to run on
|
|
top of existing networks, syndicating content through eepsites, Tor hidden services,
|
|
Freenet freesites, normal websites, usenet newgroups, email lists, RSS feeds, etc. Data
|
|
published with Syndie is done so as to offer pseudonymous authentication to anyone
|
|
reading or archiving it.
|
|
</p>
|
|
|
|
<h2 id="app.i2ptunnel">I2PTunnel</h2>
|
|
<p><i>Developed by: mihi</i></p>
|
|
|
|
<p>
|
|
I2PTunnel is probably I2P's most popular and versatile client application, allowing
|
|
generic proxying both into and out of the I2P network. I2PTunnel can be viewed as
|
|
four separate proxying applications - a "client" which receives inbound TCP connections
|
|
and forwards them to a given I2P destination, an "httpclient" (aka "eepproxy") which
|
|
acts like an HTTP proxy and forwards the requests to the appropriate I2P destination
|
|
(after querying the naming service if necessary), a "server" which receives inbound I2P
|
|
streaming connections on a destination and forwards them to a given TCP host+port,
|
|
and an "httpserver" which extends the "server" by parsing the HTTP request and
|
|
responses to allow safer operation. There is an additional "socksclient" application,
|
|
but its use is not encouraged for reasons previously mentioned.
|
|
</p>
|
|
|
|
<p>
|
|
I2P itself is not an outproxy network - the anonymity and security concerns inherent
|
|
in a mix net which forwards data into and out of the mix have kept I2P's design focused
|
|
on providing an anonymous network which capable of meeting the user's needs without
|
|
requiring external resources. However, the I2PTunnel "httpclient" application offers
|
|
a hook for outproxying - if the hostname requested doesn't end in ".i2p", it picks a
|
|
random destination from a user-provided set of outproxies and forwards the request to
|
|
them. These destinations are simply I2PTunnel "server" instances run by volunteers
|
|
who have explicitly chosen to run outproxies - no one is an outproxy by default, and
|
|
running an outproxy doesn't automatically tell other people to proxy through you.
|
|
While outproxies do have inherent weaknesses, they offer a simple proof of concept for
|
|
using I2P and provide some functionality under a threat model which may be sufficient
|
|
for some users.
|
|
</p>
|
|
|
|
<p>
|
|
I2PTunnel enables most of the applications in use. An "httpserver" pointing at a
|
|
webserver lets anyone run their own anonymous website (or "eepsite") - a webserver
|
|
is bundled with I2P for this purpose, but any webserver can be used. Anyone may
|
|
run a "client" pointing at one of the anonymously hosted IRC servers, each of which
|
|
are running a "server" pointing at their local IRCd and communicating between IRCds
|
|
over their own "client" tunnels. End users also have "client" tunnels pointing at
|
|
<a href="#app.i2pmail">I2Pmail's</a> POP3 and SMTP destinations (which in turn are
|
|
simply "server" instances pointing at POP3 and SMTP servers), as well as "client"
|
|
tunnels pointing at I2P's CVS server, allowing anonymous development. At times people have
|
|
even run "client" proxies to access the "server" instances pointing at an NNTP server.
|
|
</p>
|
|
|
|
<h2 id="app.i2pbt">i2p-bt</h2>
|
|
<p><i>Developed by: duck, et al</i></p>
|
|
|
|
<p>
|
|
i2p-bt is a port of the mainline python BitTorrent client to run both the tracker and
|
|
peer communication over I2P. Tracker requests are forwarded through the eepproxy to
|
|
eepsites specified in the torrent file while tracker responses refer to peers by their
|
|
destination explicitly, allowing i2p-bt to open up a
|
|
<a href="#app.streaming">streaming lib</a> connection to query them for blocks.
|
|
</p>
|
|
|
|
<p>
|
|
In addition to i2p-bt, a port of bytemonsoon has been made to I2P, making a few
|
|
modifications as necessary to strip any anonymity-compromising information from the
|
|
application and to take into consideration the fact that IPs cannot be used for
|
|
identifying peers.
|
|
</p>
|
|
|
|
<h2 id="app.i2psnark">I2PSnark</h2>
|
|
<p><i>I2PSnark developed: jrandom, et al, ported from <a
|
|
href="http://www.klomp.org/mark/">mjw</a>'s <a
|
|
href="http://www.klomp.org/snark/">Snark</a> client</i></p>
|
|
|
|
<p>
|
|
Bundled with the I2P install, I2PSnark offers a simple anonymous bittorrent
|
|
client with multitorrent capabilities, exposing all of the functionality through
|
|
a plain HTML web interface.
|
|
</p>
|
|
|
|
<h2 id="app.azneti2p">Azureus/azneti2p</h2>
|
|
<p><i>Developed by: parg, et al</i></p>
|
|
|
|
<p>
|
|
The developers of the <a href="http://azureus.sf.net/">Azureus</a> BitTorrent client
|
|
have created an "azneti2p" plugin, allowing Azureus users to participate in anonymous
|
|
swarms over I2P, or simply to access anonymously hosted trackers while contacting
|
|
each peer directly. In addition, Azureus' built in tracker lets people run their
|
|
own anonymous trackers without running bytemonsoon (which has substantial prerequisites)
|
|
or i2p-bt's tracker. The plugin is currently (July 2005) fully functional, but is in early
|
|
beta and has a fairly complicated configuration process, though it is hopefully going
|
|
to be streamlined further.
|
|
</p>
|
|
|
|
<h2 id="app.i2phex">I2Phex</h2>
|
|
<p><i>Developed by: sirup</i></p>
|
|
|
|
<p>
|
|
I2Phex is a fairly direct port of the Phex Gnutella filesharing client to run
|
|
entirely on top of I2P. While it has disabled some of Phex's functionality,
|
|
such as integration with Gnutella webcaches, the basic file sharing and chatting
|
|
system is fully functional.
|
|
</p>
|
|
|
|
<h2 id="app.i2pmail">I2Pmail/susimail</h2>
|
|
<p><i>Developed by: postman, susi23, mastiejaner</i></p>
|
|
|
|
<p>
|
|
I2Pmail is more a service than an application - postman offers both internal and
|
|
external email with POP3 and SMTP service through I2PTunnel instances accessing a
|
|
series of components developed with mastiejaner, allowing people to use their
|
|
preferred mail clients to send and receive mail pseudonymously. However, as most
|
|
mail clients expose substantial identifying information, I2P bundles susi23's
|
|
web based susimail client which has been built specifically with I2P's anonymity
|
|
needs in mind. The I2Pmail/mail.i2p service offers transparent virus filtering as
|
|
well as denial of service prevention with hashcash augmented quotas.
|
|
In addition, each user has control of their batching strategy prior to delivery
|
|
through the mail.i2p outproxies, which are separate from the mail.i2p SMTP and
|
|
POP3 servers - both the outproxies and inproxies communicate with the mail.i2p
|
|
SMTP and POP3 servers through I2P itself, so compromising those non-anonymous
|
|
locations does not give access to the mail accounts or activity patterns of the
|
|
user. At the moment the developers work on a decentralized mailsystem, called
|
|
"v2mail". More information can be found on the eepsite
|
|
<a href="http://hq.postman.i2p/">hq.postman.i2p</a>.
|
|
</p>
|
|
|
|
</body>
|
|
</html>
|