update dht_sec specification and the dht code
This commit is contained in:
Arvid Norberg
parent
d09e958166
commit
49a1398fe5
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@ -3,7 +3,7 @@
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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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<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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<meta name="generator" content="Docutils 0.8.1: 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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@ -93,7 +93,7 @@ by observing that a typical routing table typically has about 20 of its
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top routing table buckets full. That means the key space is dense enough
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to contain 8 nodes for every combination of the 20 top bits of node IDs.</p>
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<blockquote>
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<tt class="docutils literal"><span class="pre">2^20</span> <span class="pre">*</span> <span class="pre">8</span> <span class="pre">=</span> <span class="pre">8388608</span></tt></blockquote>
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<tt class="docutils literal">2^20 * 8 = 8388608</tt></blockquote>
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<p>By controlling that many IP addresses, an attacker could snoop any info-hash.
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By controlling 8 times that many IP addresses, an attacker could actually
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take over any info-hash.</p>
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@ -109,18 +109,20 @@ of IPs, as well as allowing more than one node ID per external IP, the node
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ID can be restricted at each class level of the IP.</p>
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<p>The expression to calculate a valid ID prefix (from an IPv4 address) is:</p>
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<pre class="literal-block">
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sha1((A * (B * (C * (D * (rand() % 8) % 0x100) % 0x4000) % 0x100000)) % 0x4000000)
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sha1((ip & 0x30f3fff) .. r)
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</pre>
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<p>Where <tt class="docutils literal"><span class="pre">A</span></tt>, <tt class="docutils literal"><span class="pre">B</span></tt>, <tt class="docutils literal"><span class="pre">C</span></tt> and <tt class="docutils literal"><span class="pre">D</span></tt> are the four octets of an IPv4 address.</p>
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<p>The pattern is that the modulus constant is shifted left by 6 for each octet.
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It generalizes to IPv6 by only considering the first 64 bit of the IP (since
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the low 64 bits are controlled by the host) and shifting the modulus by 3 for
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each octet instead.</p>
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<p>And for an IPv6 address (<tt class="docutils literal">ip</tt> is the high 64 bits of the address):</p>
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<pre class="literal-block">
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sha1((ip & 0x103070f1f3f7fff) .. r)
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</pre>
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<p><tt class="docutils literal">r</tt> is a random number in the range [0, 7]. The resulting integer,
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representing the masked IP address is supposed to be big-endian before
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hashed. The ".." means concatenation.</p>
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<p>The details of implementing this is to evaluate the expression, store the
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result in a big endian 32 bit integer and hash those 4 bytes with SHA-1.
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The first 4 bytes of the node ID used in the DHT MUST match the first 4
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result in a big endian 64 bit integer and hash those 8 bytes with SHA-1.</p>
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<p>The first 4 bytes of the node ID used in the DHT MUST match the first 4
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bytes in the resulting hash. The last byte of the hash MUST match the
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random number used to generate the hash.</p>
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random number (<tt class="docutils literal">r</tt>) used to generate the hash.</p>
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<img alt="ip_id_v4.png" src="ip_id_v4.png" />
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<img alt="ip_id_v6.png" src="ip_id_v6.png" />
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<p>Example code code for calculating a valid node ID:</p>
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@ -129,63 +131,45 @@ uint8_t* ip; // our external IPv4 or IPv6 address (network byte order)
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int num_octets; // the number of octets to consider in ip (4 or 8)
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uint8_t node_id[20]; // resulting node ID
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uint32_t rand = rand() & 0xff;
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uint32_t modulus = 0x100;
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uint32_t seed = rand & 0x7;
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int mod_shift = 6 * 4 / num_octets; // 6 or 3, depending on IPv4 and IPv6
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while (num_octets)
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{
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seed = (uint64_t(seed) * ip[num_octets-1]) & (modulus-1);
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modulus <<= mod_shift;
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--num_octets;
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}
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uint8_t v4mask[] = { 0x03, 0x0f, 0x3f, 0xff };
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uint8_t v6mask[] = { 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff };
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uint8_t* mask = num_octets == 4 ? v4_mask : v8_mask;
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for (int i = 0; i < num_octets; ++i)
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ip[i] &= mask[i];
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seed = htonl(seed);
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SHA_CTX ctx;
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SHA1_Init(&ctx);
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SHA1_Update(&ctx, (unsigned char*)&seed, sizeof(seed));
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SHA1_Update(&ctx, (unsigned char*)ip, num_octets);
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uint32_t rand = rand() & 0xff;
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uint8_t r = rand & 0x7;
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SHA1_Update(&ctx, (unsigned char*)&r, 1);
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SHA1_Final(&ctx, node_id);
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for (int i = 4; i < 19; ++i) node_id[i] = rand();
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node_id[19] = rand;
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</pre>
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<p>Example code to verify a node ID:</p>
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<pre class="literal-block">
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uint8_t* ip; // incoming IPv4 or IPv6 address (network byte order)
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int num_octets; // the number of octets to consider in ip (4 or 8)
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uint8_t node_id[20]; // incoming node ID
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uint32_t modulus = 0x100;
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uint32_t seed = node_id[19] & 0x7;
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int mod_shift = 6 * 4 / num_octets; // 6 or 3, depending on IPv4 and IPv6
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while (num_octets)
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{
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seed = (uint64_t(seed) * ip[num_octets-1]) & (modulus-1);
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modulus <<= mod_shift;
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--num_octets;
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}
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seed = htonl(seed);
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SHA_CTX ctx;
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SHA1_Init(&ctx);
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SHA1_Update(&ctx, (unsigned char*)&seed, sizeof(seed));
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uint8_t digest[20];
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SHA1_Final(&ctx, digest);
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if (memcmp(digest, node_id, 4) != 0)
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return false; // failed verification
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else
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return true; // verification passed
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</pre>
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<p>test vectors:</p>
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<pre class="literal-block">
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IP rand example node ID
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============ ===== ==========================================
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124.31.75.21 1 <strong>8a84ac4d</strong> 0c5d6a4ec8a88e4c6ab4c28b95eee4 <strong>01</strong>
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21.75.31.124 86 <strong>b25a51b1</strong> 4e7a08645677bbd1cfe7d8f956d532 <strong>56</strong>
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65.23.51.170 22 <strong>dc35968d</strong> bc8f112a3d426c84764f8c2a1150e6 <strong>16</strong>
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84.124.73.14 65 <strong>98f44bb1</strong> 1bb1fe518101ceef99462b947a01ff <strong>41</strong>
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43.213.53.83 90 <strong>5978e1c4</strong> 5b7c4be0237986d5243b87aa6d5130 <strong>5a</strong>
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</pre>
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<p>The bold parts of the node ID are the important parts. The rest are
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random numbers.</p>
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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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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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extra result value (inside the <tt class="docutils literal">r</tt> dictionary) called <tt class="docutils literal">ip</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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This is the same byte sequence used to verify the node ID.</p>
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<p>A DHT node which receives an <tt class="docutils literal">ip</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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@ -197,7 +181,7 @@ nodes, from separate searches, tells you your node ID is incorrect.</p>
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<p>Once enforced, write tokens from peers whose node ID does not match its external
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IP should be considered dropped. In other words, a peer that uses a non-matching
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ID MUST 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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original DHT specification only <tt class="docutils literal">announce_peer</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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@ -65,20 +65,22 @@ ID can be restricted at each class level of the IP.
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The expression to calculate a valid ID prefix (from an IPv4 address) is::
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sha1((A * (B * (C * (D * (rand() % 8) % 0x100) % 0x4000) % 0x100000)) % 0x4000000)
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sha1((ip & 0x30f3fff) .. r)
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Where ``A``, ``B``, ``C`` and ``D`` are the four octets of an IPv4 address.
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And for an IPv6 address (``ip`` is the high 64 bits of the address)::
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The pattern is that the modulus constant is shifted left by 6 for each octet.
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It generalizes to IPv6 by only considering the first 64 bit of the IP (since
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the low 64 bits are controlled by the host) and shifting the modulus by 3 for
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each octet instead.
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sha1((ip & 0x103070f1f3f7fff) .. r)
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``r`` is a random number in the range [0, 7]. The resulting integer,
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representing the masked IP address is supposed to be big-endian before
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hashed. The ".." means concatenation.
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The details of implementing this is to evaluate the expression, store the
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result in a big endian 32 bit integer and hash those 4 bytes with SHA-1.
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result in a big endian 64 bit integer and hash those 8 bytes with SHA-1.
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The first 4 bytes of the node ID used in the DHT MUST match the first 4
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bytes in the resulting hash. The last byte of the hash MUST match the
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random number used to generate the hash.
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random number (``r``) used to generate the hash.
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.. image:: ip_id_v4.png
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.. image:: ip_id_v6.png
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@ -89,63 +91,47 @@ Example code code for calculating a valid node ID::
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int num_octets; // the number of octets to consider in ip (4 or 8)
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uint8_t node_id[20]; // resulting node ID
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uint32_t rand = rand() & 0xff;
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uint32_t modulus = 0x100;
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uint32_t seed = rand & 0x7;
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int mod_shift = 6 * 4 / num_octets; // 6 or 3, depending on IPv4 and IPv6
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while (num_octets)
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{
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seed = (uint64_t(seed) * ip[num_octets-1]) & (modulus-1);
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modulus <<= mod_shift;
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--num_octets;
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}
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uint8_t v4mask[] = { 0x03, 0x0f, 0x3f, 0xff };
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uint8_t v6mask[] = { 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff };
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uint8_t* mask = num_octets == 4 ? v4_mask : v8_mask;
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for (int i = 0; i < num_octets; ++i)
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ip[i] &= mask[i];
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seed = htonl(seed);
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SHA_CTX ctx;
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SHA1_Init(&ctx);
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SHA1_Update(&ctx, (unsigned char*)&seed, sizeof(seed));
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SHA1_Update(&ctx, (unsigned char*)ip, num_octets);
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uint32_t rand = rand() & 0xff;
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uint8_t r = rand & 0x7;
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SHA1_Update(&ctx, (unsigned char*)&r, 1);
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SHA1_Final(&ctx, node_id);
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for (int i = 4; i < 19; ++i) node_id[i] = rand();
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node_id[19] = rand;
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Example code to verify a node ID::
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uint8_t* ip; // incoming IPv4 or IPv6 address (network byte order)
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int num_octets; // the number of octets to consider in ip (4 or 8)
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uint8_t node_id[20]; // incoming node ID
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uint32_t modulus = 0x100;
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uint32_t seed = node_id[19] & 0x7;
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int mod_shift = 6 * 4 / num_octets; // 6 or 3, depending on IPv4 and IPv6
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while (num_octets)
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{
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seed = (uint64_t(seed) * ip[num_octets-1]) & (modulus-1);
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modulus <<= mod_shift;
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--num_octets;
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}
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seed = htonl(seed);
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SHA_CTX ctx;
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SHA1_Init(&ctx);
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SHA1_Update(&ctx, (unsigned char*)&seed, sizeof(seed));
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uint8_t digest[20];
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SHA1_Final(&ctx, digest);
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if (memcmp(digest, node_id, 4) != 0)
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return false; // failed verification
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else
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return true; // verification passed
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test vectors:
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.. parsed-literal::
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IP rand example node ID
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============ ===== ==========================================
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124.31.75.21 1 **8a84ac4d** 0c5d6a4ec8a88e4c6ab4c28b95eee4 **01**
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21.75.31.124 86 **b25a51b1** 4e7a08645677bbd1cfe7d8f956d532 **56**
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65.23.51.170 22 **dc35968d** bc8f112a3d426c84764f8c2a1150e6 **16**
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84.124.73.14 65 **98f44bb1** 1bb1fe518101ceef99462b947a01ff **41**
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43.213.53.83 90 **5978e1c4** 5b7c4be0237986d5243b87aa6d5130 **5a**
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The bold parts of the node ID are the important parts. The rest are
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random numbers.
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bootstrapping
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-------------
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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, *all* DHT requests whose node
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is not a trivial problem. With this extension, *all* 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 ``r`` dictionary) called ``ip``. 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.
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This is the same byte sequence used to verify the node ID.
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A DHT node which receives an ``ip`` 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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@ -98,48 +98,43 @@ int distance_exp(node_id const& n1, node_id const& n2)
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struct static_ { static_() { std::srand((unsigned int)std::time(0)); } } static__;
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node_id generate_id_impl(address const& ip, boost::uint32_t r)
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node_id generate_id_impl(address const& ip_, boost::uint32_t r)
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{
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boost::uint32_t seed = r & 0x7;
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boost::uint32_t modulus = 0x100;
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boost::uint8_t* p = 0;
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int num_octets = 0;
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int mod_shift = 0;
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boost::uint8_t* ip = 0;
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const static uint8_t v4mask[] = { 0x03, 0x0f, 0x3f, 0xff };
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const static uint8_t v6mask[] = { 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff };
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uint8_t const* mask = 0;
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int num_octets = 0;
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address_v4::bytes_type b4;
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#if TORRENT_USE_IPV6
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address_v6::bytes_type b6;
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if (ip.is_v6())
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if (ip_.is_v6())
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{
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b6 = ip.to_v6().to_bytes();
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p = &b6[0];
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b6 = ip_.to_v6().to_bytes();
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ip = &b6[0];
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num_octets = 8;
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mod_shift = 3;
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mask = v6mask;
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}
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else
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#endif
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{
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b4 = ip.to_v4().to_bytes();
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p = &b4[0];
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b4 = ip_.to_v4().to_bytes();
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ip = &b4[0];
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num_octets = 4;
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mod_shift = 6;
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mask = v4mask;
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}
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while (num_octets)
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{
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seed *= p[num_octets-1];
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seed &= (modulus-1);
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modulus <<= mod_shift;
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--num_octets;
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}
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seed = htonl(seed);
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node_id id = hasher((const char*)&seed, sizeof(seed)).final();
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for (int i = 0; i < num_octets; ++i)
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ip[i] &= mask[i];
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hasher h;
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h.update((char*)ip, num_octets);
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uint8_t rand = r & 0x7;
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h.update((char*)&r, 1);
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node_id id = h.final();
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for (int i = 4; i < 19; ++i) id[i] = random();
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id[19] = r;
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return id;
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@ -68,6 +68,11 @@ using namespace boost::tuples;
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namespace libtorrent {
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TORRENT_EXPORT std::string sanitize_path(std::string const& p);
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namespace dht
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{
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TORRENT_EXPORT libtorrent::dht::node_id generate_id_impl(
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address const& ip_, boost::uint32_t r);
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}
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}
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sha1_hash to_hash(char const* s)
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@ -1714,10 +1719,39 @@ int test_main()
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}
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TEST_CHECK(hits > int(temp.size()) / 2);
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using namespace libtorrent::dht;
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char const* ips[] = {
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"124.31.75.21",
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"21.75.31.124",
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"65.23.51.170",
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"84.124.73.14",
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"43.213.53.83",
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};
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int rs[] = { 1,86,22,65,90 };
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boost::uint8_t prefixes[][4] =
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{
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{0x8a, 0x84, 0xac, 0x4d},
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||||
{0xb2, 0x5a, 0x51, 0xb1 },
|
||||
{0xdc, 0x35, 0x96, 0x8d },
|
||||
{0x98, 0xf4, 0x4b, 0xb1 },
|
||||
{0x59, 0x78, 0xe1, 0xc4 },
|
||||
};
|
||||
|
||||
for (int i = 0; i < 5; ++i)
|
||||
{
|
||||
address a = address_v4::from_string(ips[i]);
|
||||
node_id id = generate_id_impl(a, rs[i]);
|
||||
for (int j = 0; j < 4; ++j)
|
||||
TEST_CHECK(id[j] == prefixes[i][j]);
|
||||
TEST_CHECK(id[19] == rs[i]);
|
||||
fprintf(stderr, "IP address: %s r: %d node ID: %s\n", ips[i]
|
||||
, rs[i], to_hex(id.to_string()).c_str());
|
||||
}
|
||||
#endif
|
||||
|
||||
|
||||
|
||||
// test peer_id/sha1_hash type
|
||||
|
||||
sha1_hash h1(0);
|
||||
|
|
|
|||
Loading…
Reference in New Issue