fix bug in ed25519 DHT signature verification. removed RSA code as it's no longer used. add CAS feature (compare and swap) to DHT put command. update dht_store documentation
This commit is contained in:
Arvid Norberg
@@ -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 0.11: http://docutils.sourceforge.net/" />
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<meta name="generator" content="Docutils 0.10: http://docutils.sourceforge.net/" />
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<title>BitTorrent extension for arbitrary DHT store</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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@@ -192,7 +192,7 @@ number to a lower one, only upgrade. The sequence number SHOULD not exceed <tt c
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(i.e. <tt class="docutils literal">0x7fffffffffffffff</tt>. A client MAY reject any message with a sequence number
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exceeding this.</p>
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<p>The signature is a 64 byte ed25519 signature of the bencoded sequence
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number and <tt class="docutils literal">v</tt> key. e.g. something like this:: <tt class="docutils literal">3:seqi4e1:v12:Hello world!</tt>.</p>
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number concatenated with the <tt class="docutils literal">v</tt> key. e.g. something like this:: <tt class="docutils literal">3:seqi4e1:v12:Hello world!</tt>.</p>
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<div class="section" id="id1">
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<h2>put message</h2>
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<p>Request:</p>
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@@ -200,6 +200,7 @@ number and <tt class="docutils literal">v</tt> key. e.g. something like this:: <
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{
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"a":
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{
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"cas": <em><optional 20 byte hash (string)></em>,
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"id": <em><20 byte id of sending node (string)></em>,
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"k": <em><ed25519 public key (32 bytes string)></em>,
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"seq": <em><monotonically increasing sequence number (integer)></em>,
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@@ -216,9 +217,18 @@ number and <tt class="docutils literal">v</tt> key. e.g. something like this:: <
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to what's already stored on the node, MUST reject the request. If the sequence
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number is equal, and the value is also the same, the node SHOULD reset its timeout
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counter.</p>
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<p>If the sequence number in the <tt class="docutils literal">put</tt> message is lower than the sequence number
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associated with the currently stored value, the storing node MAY return an error
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message with code 302 (see error codes below).</p>
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<p>Note that this request does not contain a target hash. The target hash under
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which this blob is stored is implied by the <tt class="docutils literal">k</tt> argument. The key is
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the SHA-1 hash of the key (<tt class="docutils literal">k</tt>).</p>
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<p>The <tt class="docutils literal">cas</tt> field is optional. If present it is interpreted of the sha-1 hash of
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the sequence number and <tt class="docutils literal">v</tt> field that is expected to be replaced. The buffer
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to hash is the same as the one signed when storing. <tt class="docutils literal">cas</tt> is short for <em>compare
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and swap</em>, it has similar semantics as CAS CPU instructions. If specified as part
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of the put command, and the current value stored under the public key differs from
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the expected value, the store fails. The <tt class="docutils literal">cas</tt> field only applies to mutable puts.</p>
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<p>Response:</p>
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<pre class="literal-block">
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{
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@@ -227,6 +237,52 @@ the SHA-1 hash of the key (<tt class="docutils literal">k</tt>).</p>
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"y": "r",
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}
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</pre>
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<p>If the store fails for any reason an error message is returned instead of the message
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template above, i.e. one where "y" is "e" and "e" is a tuple of [error-code, message]).
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Failures include where the <tt class="docutils literal">cas</tt> hash mismatches and the sequence number is outdated.</p>
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<p>If no <tt class="docutils literal">cas</tt> field is included in the <tt class="docutils literal">put</tt> message, the value of the current <tt class="docutils literal">v</tt>
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field should be disregarded when determining whether or not to save the item.</p>
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<p>The error message (as specified by <a class="reference external" href="http://www.bitorrent.org/beps/bep0005.html">BEP5</a>) looks like this:</p>
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<pre class="literal-block">
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{
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"e": [ <em><error-code (integer)></em>, <em><error-string (string)></em> ],
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"t": <em><transaction-id (string)></em>,
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"y": "e",
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}
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</pre>
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<p>In addition to the error codes defined in <a class="reference external" href="http://www.bitorrent.org/beps/bep0005.html">BEP5</a>, this specification defines
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some additional error codes.</p>
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<table border="1" class="docutils">
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<colgroup>
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<col width="29%" />
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<col width="71%" />
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</colgroup>
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<thead valign="bottom">
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<tr><th class="head">error-code</th>
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<th class="head">description</th>
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</tr>
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</thead>
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<tbody valign="top">
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<tr><td>205</td>
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<td>message (i.e. <tt class="docutils literal">v</tt> field)
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too big.</td>
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</tr>
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<tr><td>206</td>
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<td>invalid signature</td>
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</tr>
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<tr><td>301</td>
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<td>the CAS hash mismatched,
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re-read value and try
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again.</td>
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</tr>
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<tr><td>302</td>
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<td>sequence number less than
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current.</td>
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</tr>
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</tbody>
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</table>
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<p>An implementation MUST emit 301 errors if the cas-hash mismatches. This is
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a critical feature in synchronization of multiple agents sharing an immutable item.</p>
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</div>
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<div class="section" id="id2">
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<h2>get message</h2>
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@@ -265,12 +321,13 @@ the SHA-1 hash of the key (<tt class="docutils literal">k</tt>).</p>
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</div>
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<div class="section" id="signature-verification">
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<h1>signature verification</h1>
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<p>The signature, private and public keys are in the format as produced by this derivative <a class="reference external" href="https://github.com/nightcracker/ed25519">ed25519 library</a>.</p>
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<p>In order to make it maximally difficult to attack the bencoding parser, signing and verification of the
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value and sequence number should be done as follows:</p>
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<ol class="arabic simple">
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<li>encode value and sequence number separately</li>
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<li>concatenate "3:seqi" <tt class="docutils literal">seq</tt> "e1:v" and the encoded value.
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sequence number 1 of value "Hello World!" would be converted to: 3:seqi1e1:v12:Hello World!
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<li>concatenate <em>"3:seqi"</em> <tt class="docutils literal">seq</tt> <em>"e1:v"</em> <tt class="docutils literal">len</tt> <em>":"</em> and the encoded value.
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sequence number 1 of value "Hello World!" would be converted to: "3:seqi1e1:v12:Hello World!"
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In this way it is not possible to convince a node that part of the length is actually part of the
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sequence number even if the parser contains certain bugs. Furthermore it is not possible to have a
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verification failure if a bencoding serializer alters the order of entries in the dictionary.</li>
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@@ -286,8 +343,8 @@ the response SHOULD be considered invalid.</p>
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<h1>expiration</h1>
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<p>Without re-announcement, these items MAY expire in 2 hours. In order
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to keep items alive, they SHOULD be re-announced once an hour.</p>
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<p>Subscriber nodes MAY help out in announcing items the are interested in to the DHT,
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to keep them alive.</p>
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<p>Any node that's interested in keeping a blob in the DHT alive may announce it. It would simply
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repeat the signature for a mutable put without having the private key.</p>
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</div>
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<div class="section" id="test-vectors">
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<h1>test vectors</h1>
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