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lolstorage.html
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<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
lang="en" xml:lang="en">
<head>
<title>lolstorage: laughably good social networking and content sharing</title>
<meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"/>
<meta name="generator" content="Org-mode"/>
<meta name="generated" content="2012-04-28 18:34:58 CEST"/>
<meta name="author" content="Manuel Simoni"/>
<meta name="description" content=""/>
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<body>
<div id="content">
<h1 class="title">lolstorage: laughably good social networking and content sharing</h1>
<p>Lolstorage is now at <a href="https://github.com/manuel/lolstorage">https://github.com/manuel/lolstorage</a>. The text
below is of an older design.
</p>
<hr/>
<div id="table-of-contents">
<h2>Table of Contents</h2>
<div id="text-table-of-contents">
<ul>
<li><a href="#sec-1">Description </a></li>
<li><a href="#sec-2">Cryptography </a></li>
<li><a href="#sec-3">Storage </a></li>
<li><a href="#sec-4">Server Protocol </a></li>
</ul>
</div>
</div>
<div id="outline-container-1" class="outline-2">
<h2 id="sec-1">Description </h2>
<div class="outline-text-2" id="text-1">
<p>
<i>lolstorage</i>'s approach to P2P <a href="http://twitter.com"><i>social networking</i></a> and <i>content sharing</i> is to layer a <i>Git</i>-style model with <i>commits</i> and
<i>trees-of-hashes</i> (for representing histories of filesystem trees) on
top of a <i>cryptographic capability</i> system inspired by <a href="http://tahoe-lafs.org/~zooko/lafs.pdf"><i>Tahoe-LAFS</i></a>
(for integrity and privacy of content even when stored on untrusted
providers). It runs in the browser in JavaScript and uses local
storage APIs. Application data is stored as filesystem trees. An
example Twitter-like app may store a user's tweets in a YYYY/MM/DD
directory structure.
</p>
<p>
The user's <i>wallet</i> contains write-caps for the user's <i>refs</i> (which
are mutable pointers to commits), and is encrypted with a
passphrase. The user may generate a read-cap for a ref and share it
with other peers. This read-cap allows the peers to locally <i>clone</i>
the state of the shared ref, which is similar to <i>following</i> in
Twitter. The local clone can be updated efficiently, using similar
methods as those used in Git fetching and pushing. There is no shared
state; only a single user ever writes to a ref. Presented to users is
a locally computed <i>overlay</i> of content from local and cloned remote
refs (e.g. a Twitter-like timeline) that may index the content to
provide services like search and sorted and aggregated views.
</p>
<p>
The resulting system is simple, secure, and disruption-tolerant
vaporware.
</p>
</div>
</div>
<div id="outline-container-2" class="outline-2">
<h2 id="sec-2">Cryptography </h2>
<div class="outline-text-2" id="text-2">
<p>These constructions are based on <a href="http://tahoe-lafs.org/~zooko/lafs.pdf"><i>Tahoe-LAFS</i></a>. I more or less
directly copied them, hoping to keep all of their security features
intact. They are simpler because files are not split into
Reed-Solomon encoded shares.
</p>
</div>
<div id="outline-container-2.1" class="outline-3">
<h3 id="sec-2.1">Objects </h3>
<div class="outline-text-3" id="text-2.1">
<p>
An immutable object is either a blob, a tree, or a commit.
</p>
<p>
Objects are encrypted using a fresh encryption key and stored under
the hash of their ciphertext.
</p>
<p>
The verify cap for an object contains the ciphertext hash, allowing
verification of stored content.
</p>
<p>
The read cap for an object contains the verify cap and the encryption
key, allowing decryption of stored content.
</p>
<p>
<a href="#[sec-2.1"><img src="lolstorage/diagrams/immutable.png"/></a>
</p>
</div>
<div id="outline-container-2.1.1" class="outline-4">
<h4 id="sec-2.1.1">To write an immutable object </h4>
<div class="outline-text-4" id="text-2.1.1">
<ul>
<li>
Generate encryption key
</li>
<li>
Encrypt data using encryption key
</li>
<li>
Create verify cap by hashing ciphertext
</li>
<li>
Write ciphertext to store using verify cap as storage index
</li>
<li>
Return immutable read cap containing verify cap and encryption key
</li>
</ul>
</div>
</div>
<div id="outline-container-2.1.2" class="outline-4">
<h4 id="sec-2.1.2">To read an immutable object given a read cap </h4>
<div class="outline-text-4" id="text-2.1.2">
<ul>
<li>
Read ciphertext from store using verify cap as storage index
</li>
<li>
Check that ciphertext hashes to verify cap
</li>
<li>
Decrypt ciphertext using encryption key
</li>
</ul>
</div>
</div>
</div>
<div id="outline-container-2.2" class="outline-3">
<h3 id="sec-2.2">Refs </h3>
<div class="outline-text-3" id="text-2.2">
<p>
A mutable ref "points to" the current commit: it contains an immutable
read cap for the commit.
</p>
<p>
For every mutable ref, a private-key pair is created. The owner of
the ref has the private key, and thus can sign new versions of the
ref.
</p>
<p>
<a href="#[sec-2.2"><img src="lolstorage/diagrams/mutable.png"/></a>
</p>
</div>
<div id="outline-container-2.2.1" class="outline-4">
<h4 id="sec-2.2.1">To write a mutable ref </h4>
<div class="outline-text-4" id="text-2.2.1">
<ul>
<li>
Create read key by hashing private key
</li>
<li>
Generate salt
</li>
<li>
Create encryption key by hashing salt and read key
</li>
<li>
Encrypt ref value using encryption key
</li>
<li>
Sign ciphertext and salt using private key
</li>
<li>
Create content from ciphertext, salt, signature, and public key
</li>
<li>
Create verify cap by hashing public key
</li>
<li>
Write content to store using verify cap as storage index
</li>
<li>
Return mutable read cap containing verify cap and read key
</li>
</ul>
</div>
</div>
<div id="outline-container-2.2.2" class="outline-4">
<h4 id="sec-2.2.2">To read a mutable ref given a mutable read cap </h4>
<div class="outline-text-4" id="text-2.2.2">
<ul>
<li>
Read ciphertext, salt, signature, and public key from store
using verify cap as storage index
</li>
<li>
Check that public key hashes to verify cap
</li>
<li>
Verify signature of salt and ciphertext using public key
</li>
<li>
Create encryption key from salt and read key
</li>
<li>
Decrypt ciphertext using encryption key
</li>
</ul>
</div>
</div>
</div>
</div>
<div id="outline-container-3" class="outline-2">
<h2 id="sec-3">Storage </h2>
<div class="outline-text-2" id="text-3">
<p>All binary data is encoded using <a href="http://en.wikipedia.org/wiki/Base64#URL_applications">"modified Base64 for URL"</a> encoding,
with "-" and "_" as additional characters beyond [A-Z][a-z][0-9], and
requiring no trailing padding characters.
</p>
<p>
Some data may contain <a href="http://cr.yp.to/proto/netstrings.txt">netstrings</a> for additional structure. A
<i>netlist</i> is a netstring containing further netstrings as components.
</p>
</div>
<div id="outline-container-3.1" class="outline-3">
<h3 id="sec-3.1">Capabilities </h3>
<div class="outline-text-3" id="text-3.1">
</div>
<div id="outline-container-3.1.1" class="outline-4">
<h4 id="sec-3.1.1">Verify Caps </h4>
<div class="outline-text-4" id="text-3.1.1">
<p>
Base64-encoded binary data.
</p>
</div>
</div>
<div id="outline-container-3.1.2" class="outline-4">
<h4 id="sec-3.1.2">Read Caps </h4>
<div class="outline-text-4" id="text-3.1.2">
<p>
Read capabilities are two-component netlists, containing the verify
cap and the Base64-encoded encryption key or read key, depending on
type of read cap (immutable or mutable, respectively).
</p>
</div>
</div>
<div id="outline-container-3.1.3" class="outline-4">
<h4 id="sec-3.1.3">Private Keys </h4>
<div class="outline-text-4" id="text-3.1.3">
<p>
Base64-encoded binary data.
</p></div>
</div>
</div>
<div id="outline-container-3.2" class="outline-3">
<h3 id="sec-3.2">Objects </h3>
<div class="outline-text-3" id="text-3.2">
</div>
<div id="outline-container-3.2.1" class="outline-4">
<h4 id="sec-3.2.1">Blob </h4>
<div class="outline-text-4" id="text-3.2.1">
<p>
Base64-encoded blob data.
</p>
</div>
</div>
<div id="outline-container-3.2.2" class="outline-4">
<h4 id="sec-3.2.2">Tree </h4>
<div class="outline-text-4" id="text-3.2.2">
<p>
A <i>dentry</i> is a netlist <code>(name read-cap)</code>.
</p>
<p>
A tree is a netlist of dentries.
</p>
</div>
</div>
<div id="outline-container-3.2.3" class="outline-4">
<h4 id="sec-3.2.3">Commit </h4>
<div class="outline-text-4" id="text-3.2.3">
<p>
A <i>name/value pair</i> is a netlist <code>(name value)</code>.
</p>
<p>
A commit is a netlist containing name/value pairs:
</p>
<ul>
<li>
name: "parents", value: a netlist of read caps (typically
containing just one but defined as a list for conceptual
compatibility with Git)
</li>
<li>
name: "tree", value: read cap
</li>
</ul>
</div>
</div>
</div>
<div id="outline-container-3.3" class="outline-3">
<h3 id="sec-3.3">Refs </h3>
<div class="outline-text-3" id="text-3.3">
<p>A mutable ref stored on the server has media type "text/html".
</p>
<p>
It contains the mutable ref content (a netlist with the Base64-encoded
components ciphertext, salt, signature, public key) as a CDATA section
in a HTML element with ID "x-lolstorage-storage-object".
</p>
<p>
In addition it may include JavaScript code that launches a user
interface for viewing the ref.
</p>
</div>
</div>
</div>
<div id="outline-container-4" class="outline-2">
<h2 id="sec-4">Server Protocol </h2>
<div class="outline-text-2" id="text-4">
</div>
<div id="outline-container-4.1" class="outline-3">
<h3 id="sec-4.1">Capability URLs </h3>
<div class="outline-text-3" id="text-4.1">
<p>
Immutable objects and refs are stored on plain HTTPS servers.
</p>
<p>
The capability URL for an immutable read cap is:
</p>
<p>
<code>https://server/path/to/verify-cap.html#encryption-key</code>
</p>
<p>
The capability URL for a mutable read cap is:
</p>
<p>
<code>https://server/path/to/verify-cap.html#read-key</code>
</p>
<p>
It's important that the verify cap is the last element of the path, so
it can be mechanically extracted from the URL.
</p>
<p>
The encryption and read keys are present in the URLs after the sharp
sign fragment identifier, and thus are not sent to servers over HTTPS.
</p>
</div>
<div id="outline-container-4.1.1" class="outline-4">
<h4 id="sec-4.1.1">Alternate Servers </h4>
<div class="outline-text-4" id="text-4.1.1">
<p>
It is possible to list alternate storage servers in an URL.
</p>
<p>
This example URL includes the alternate server
<code>https://otherserver/otherpath</code> with the URL parameter "alternate1":
</p>
<p>
<code>https://server/path/to/verify-cap.html?alternate1=https%3A%2F%2Fotherserver%2Fotherpath#read-key</code>
</p>
<p>
The verify cap will be appended to alternate server, giving the
alternate capability:
</p>
<p>
<code>https://otherserver/otherpath/verify-cap.html#read-key</code>
</p>
<p>
Additional servers can be listed with alternate2, alternate3, …
</p>
</div>
</div>
</div>
<div id="outline-container-4.2" class="outline-3">
<h3 id="sec-4.2">GET /path/verify-cap.html </h3>
<div class="outline-text-3" id="text-4.2">
</div>
</div>
<div id="outline-container-4.3" class="outline-3">
<h3 id="sec-4.3">POST /path/verify-cap.html </h3>
<div class="outline-text-3" id="text-4.3">
<hr/>
</div>
</div>
</div>
<div id="postamble">
<p class="author"> Author: Manuel Simoni
<a href="mailto:msimoni@gmail.com"><msimoni@gmail.com></a>
</p>
<p class="date"> Date: 2012-04-28 18:34:58 CEST</p>
<p class="creator">HTML generated by org-mode 6.33x in emacs 23</p>
</div>
</div>
</body>
</html>