155 lines
7.2 KiB
HTML
155 lines
7.2 KiB
HTML
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<?xml version="1.0" encoding="utf-8" ?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<script type="text/javascript">
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/* <![CDATA[ */
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(function() {
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var s = document.createElement('script'), t = document.getElementsByTagName('script')[0];
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s.type = 'text/javascript';
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s.async = true;
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s.src = 'http://api.flattr.com/js/0.6/load.js?mode=auto';
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t.parentNode.insertBefore(s, t);
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})();
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/* ]]> */
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</script>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
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<title>BitTorrent DHT security extension</title>
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<meta name="author" content="Arvid Norberg, arvid@rasterbar.com" />
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<link rel="stylesheet" type="text/css" href="../../css/base.css" />
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<link rel="stylesheet" type="text/css" href="../../css/rst.css" />
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<link rel="stylesheet" href="style.css" type="text/css" />
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<style type="text/css">
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/* Hides from IE-mac \*/
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* html pre { height: 1%; }
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/* End hide from IE-mac */
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</style>
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</head>
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<body>
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<div class="document" id="bittorrent-dht-security-extension">
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<div id="container">
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<div id="headerNav">
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<ul>
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<li class="first"><a href="/">Home</a></li>
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<li><a href="../../products.html">Products</a></li>
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<li><a href="../../contact.html">Contact</a></li>
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</ul>
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</div>
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<div id="header">
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<h1><span>Rasterbar Software</span></h1>
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<h2><span>Software developement and consulting</span></h2>
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</div>
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<div id="main">
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<h1 class="title">BitTorrent DHT security extension</h1>
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<table class="docinfo" frame="void" rules="none">
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<col class="docinfo-name" />
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<col class="docinfo-content" />
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<tbody valign="top">
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<tr><th class="docinfo-name">Author:</th>
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<td>Arvid Norberg, <a class="last reference external" href="mailto:arvid@rasterbar.com">arvid@rasterbar.com</a></td></tr>
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<tr><th class="docinfo-name">Version:</th>
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<td>Draft</td></tr>
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</tbody>
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</table>
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<div class="contents topic" id="table-of-contents">
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<p class="topic-title first">Table of contents</p>
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<ul class="simple">
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<li><a class="reference internal" href="#id1" id="id2">BitTorrent DHT security extension</a></li>
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<li><a class="reference internal" href="#node-ids" id="id3">node IDs</a></li>
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<li><a class="reference internal" href="#bootstrapping" id="id4">bootstrapping</a></li>
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<li><a class="reference internal" href="#enforcement" id="id5">enforcement</a></li>
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<li><a class="reference internal" href="#backwards-compatibility-and-transition" id="id6">backwards compatibility and transition</a></li>
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</ul>
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</div>
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<div class="section" id="id1">
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<h1>BitTorrent DHT security extension</h1>
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<p>The purpose of this extension is to make it harder to launch a few
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specific attacks against the BitTorrent DHT and also to make it harder
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to snoop the network.</p>
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<p>Specifically the attack this extension intends to make harder is launching
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8 or more DHT nodes which node-IDs selected close to a specific target
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info-hash, in order to become the main nodes hosting peers for it. Currently
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this is very easy to do and lets the attacker not only see all the traffic
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related to this specific info-hash but also block access to it by other
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peers.</p>
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<p>The proposed guard against this is to enforce restrictions on which node-ID
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a node can choose, based on its external IP address.</p>
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</div>
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<div class="section" id="node-ids">
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<h1>node IDs</h1>
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<p>The proposed formula for restricting node IDs is that the 4 first bytes of
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the node ID MUST match the 4 first bytes of <tt class="docutils literal"><span class="pre">SHA-1(IP_address)</span></tt>. That is,
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the raw, big endian, storage of the address, either IPv4 or IPv6, hashed
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with SHA-1.</p>
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<p>Example:</p>
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<blockquote>
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An IP address 89.5.5.5 has a big endian byte representation of
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<tt class="docutils literal"><span class="pre">0x59</span> <span class="pre">0x05</span> <span class="pre">0x05</span> <span class="pre">0x05</span></tt>. The SHA-1 hash of this byte sequence is
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<tt class="docutils literal"><span class="pre">656d41da810a0a6d92fd2f6a8ba3b466e35ab368</span></tt>. The DHT node must choose
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a node ID which starts with <tt class="docutils literal"><span class="pre">656d41da</span></tt>.</blockquote>
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</div>
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<div class="section" id="bootstrapping">
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<h1>bootstrapping</h1>
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<p>In order to set ones initial node ID, the external IP needs to be known. This
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is not a trivial problem. WIth this extension, <em>all</em> DHT requests whose node
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ID does not match its IP address MUST be serviced and MUST also include one
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extra result value (inside the <tt class="docutils literal"><span class="pre">r</span></tt> dictionary) called <tt class="docutils literal"><span class="pre">ip</span></tt>. The IP field
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contains the raw (big endian) byte representation of the external IP address.
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This is the same byte sequence passed to SHA-1.</p>
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<p>A DHT node which receives an <tt class="docutils literal"><span class="pre">ip</span></tt> result in a request SHOULD consider restarting
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its DHT node with a new node ID, taking this IP into account. Since a single node
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can not be trusted, there should be some mechanism of determining whether or
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not the node has a correct understanding of its external IP or not. This could
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be done by voting, or only restart the DHT once at least a certain number of
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nodes, from separate searches, tells you your node ID is incorrect.</p>
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</div>
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<div class="section" id="enforcement">
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<h1>enforcement</h1>
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<p>Write tokens from peers whose node ID does not match its external IP should be
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considered dropped. In other words, a peer that uses a non-matching ID MUST
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never be used to store information on, regardless of which request. In the
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original DHT specification only <tt class="docutils literal"><span class="pre">announce_peer</span></tt> stores data in the network,
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but any future extension which stores data in the network SHOULD use the same
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restriction.</p>
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<p>Any peer on a local network address is exempt from this node ID verification.
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This includes the following IP blocks:</p>
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<dl class="docutils">
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<dt>10.0.0.0/8</dt>
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<dd>reserved for local networks</dd>
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<dt>172.16.0.0/12</dt>
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<dd>reserved for local networks</dd>
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<dt>192.168.0.0/16</dt>
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<dd>reserved for local networks</dd>
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<dt>169.254.0.0/16</dt>
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<dd>reserved for self-assigned IPs</dd>
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<dt>127.0.0.0/8</dt>
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<dd>reserved for loopback</dd>
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</dl>
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</div>
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<div class="section" id="backwards-compatibility-and-transition">
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<h1>backwards compatibility and transition</h1>
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<p>During some transition period, this restriction should not be enforced, and
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peers whose node ID does not match this formula relative to their external IP
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should not be blocked.</p>
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<p>Requests from peers whose node ID does not match their external IP should
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always be serviced, even after the transition period. The attack this protects
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from is storing data on an attacker's node, not servicing an attackers request.</p>
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</div>
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</div>
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<div id="footer">
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<span>Copyright © 2005 Rasterbar Software.</span>
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</div>
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</div>
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<script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
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</html>
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