{% extends "_layout.html" %}
{% block title %}How Garlic Routing Works{% endblock %}
{% block content %}<p>
As briefly explained on the <a href="how_intro">intro</a>, in addition to sending 
messages through tunnels (via <a href="how_tunnelrouting">tunnels</a>), I2P uses a technique called
"garlic routing" - layered encryption of messages, passing through routers 
selected by the original sender.  This is similar to the way Mixmaster
(see <a href="how_networkcomparisons">network comparisons</a>) sends messages - taking a message, encrypting it
to the recipient's public key, taking that encrypted message and encrypting
it (along with instructions specifying the next hop), and then taking that
resulting encrypted message and so on, until it has one layer of encryption
per hop along the path.  The only significant difference between that technique
and I2P's garlic routing is that at each layer, any number of messages can be
contained, instead of just a single message.

<p>
In addition to the cloves, each unwrapped garlic message contains a sender
specified amount of padding data, allowing the sender to take active countermeasures 
against traffic analysis.

<H2>Uses within I2P</H2>

<p>
I2P uses garlic routing in three places:
<UL>
<li> For building tunnels
<li> For determining the success or failure of end to end message delivery (by wrapping an additional 
     DeliveryStatusMessage in with the payload, where the clove containing the DeliveryStatusMessage 
     has instructions forwarding it back through other routers and tunnels to the original sender)

<li> For publishing some network database entries (dampening the probability of a successful traffic analysis attack)
</UL>
<p>
There are also significant ways that this technique can be used to improve the performance of the network, 
exploiting transport latency/throughput tradeoffs, and branching data through redundant paths to increase reliability.  

<H2>Encryption</H2>

<p>
The encryption of each layer in the garlic message uses the <a href="how_elgamalaes">ElGamal/AES+SessionTag</a> algorithm, 
which avoids the cost of a full 2048bit ElGamal encryption for subsequent messages (using instead a random previously 
specified SessionTag plus 256bit AES encryption).

<H2>References</H2>

<p>
The term garlic routing was first coined by Michael Freedman in Roger Dingledine's Free Haven 
<a href="http://www.freehaven.net/papers.html">Master's thesis</a> (June 2000), which was derived from 
<a href="http://onion-router.net/">Onion Routing</a>.  The main difference
from the method described by Freedman with I2P's garlic routing
is that the path is unidirectional - there is no "turning point" as seen in onion routing
or mixmaster reply blocks, which greatly simplifies the algorithm and allows for more flexible
and reliable delivery.{% endblock %}