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anonymity.html
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<!DOCTYPE html>
<html lang="en"><head>
<script src="quarto_files/clipboard/clipboard.min.js"></script>
<script src="quarto_files/quarto-html/tabby.min.js"></script>
<script src="quarto_files/quarto-html/popper.min.js"></script>
<script src="quarto_files/quarto-html/tippy.umd.min.js"></script>
<link href="quarto_files/quarto-html/tippy.css" rel="stylesheet">
<link href="quarto_files/quarto-html/light-border.css" rel="stylesheet">
<link href="quarto_files/quarto-html/quarto-html.min.css" rel="stylesheet" data-mode="light">
<link href="quarto_files/quarto-html/quarto-syntax-highlighting-dark.css" rel="stylesheet" id="quarto-text-highlighting-styles"><meta charset="utf-8">
<meta name="generator" content="quarto-1.5.56">
<title>Anonymity</title>
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no, minimal-ui">
<link rel="stylesheet" href="quarto_files/revealjs/dist/reset.css">
<link rel="stylesheet" href="quarto_files/revealjs/dist/reveal.css">
<style>
code{white-space: pre-wrap;}
span.smallcaps{font-variant: small-caps;}
div.columns{display: flex; gap: min(4vw, 1.5em);}
div.column{flex: auto; overflow-x: auto;}
div.hanging-indent{margin-left: 1.5em; text-indent: -1.5em;}
ul.task-list{list-style: none;}
ul.task-list li input[type="checkbox"] {
width: 0.8em;
margin: 0 0.8em 0.2em -1em; /* quarto-specific, see https://github.com/quarto-dev/quarto-cli/issues/4556 */
vertical-align: middle;
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/* CSS for syntax highlighting */
pre > code.sourceCode { white-space: pre; position: relative; }
pre > code.sourceCode > span { line-height: 1.25; }
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pre.numberSource code > span > a:first-child::before
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position: relative; left: -1em; text-align: right; vertical-align: baseline;
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padding: 0 4px; width: 4em;
}
pre.numberSource { margin-left: 3em; padding-left: 4px; }
div.sourceCode
{ color: #f8f8f2; }
@media screen {
pre > code.sourceCode > span > a:first-child::before { text-decoration: underline; }
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code span { color: #f8f8f2; } /* Normal */
code span.al { color: #f07178; background-color: #2a0f15; font-weight: bold; } /* Alert */
code span.an { color: #d4d0ab; } /* Annotation */
code span.at { color: #00e0e0; } /* Attribute */
code span.bn { color: #d4d0ab; } /* BaseN */
code span.bu { color: #abe338; } /* BuiltIn */
code span.cf { color: #ffa07a; font-weight: bold; } /* ControlFlow */
code span.ch { color: #abe338; } /* Char */
code span.cn { color: #ffd700; } /* Constant */
code span.co { color: #f8f8f2; font-style: italic; } /* Comment */
code span.cv { color: #ffd700; } /* CommentVar */
code span.do { color: #f8f8f2; } /* Documentation */
code span.dt { color: #ffa07a; } /* DataType */
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.callout {
margin-top: 1em;
margin-bottom: 1em;
border-radius: .25rem;
}
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border-left: solid #acacac .3rem;
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border-top: solid 1px silver;
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border-right: solid 1px silver;
border-top: solid 1px silver;
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background-size: 1rem 1rem;
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width: 0.9rem;
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background-repeat: no-repeat;
background-size: 0.9rem 0.9rem;
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margin-top: 1rem;
padding-right: .5rem;
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display: none !important;
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padding-bottom: 0.5rem;
margin-bottom: 0;
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margin-top: .5rem;
padding-right: .5rem;
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</head>
<body class="quarto-dark">
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<div class="slides">
<section id="title-slide" class="quarto-title-block center">
<h1 class="title">CS 3710</h1>
<h2 class="subtitle">Introduction to Cybersecurity</h2>
<p class="titlep"> </p>
<div class="titlesmall"><p>
<a href="http://www.cs.virginia.edu/~asb">Aaron Bloomfield</a> ([email protected])<br>
<a href="http://github.com/aaronbloomfield/ccc">@github</a> | <a href="index.html">↑</a> | <a href="?print-pdf"><img class="print" width="20" src="../slides/images/print-icon.svg" style="top:0px;vertical-align:middle;background-color:transparent"></a>
</p></div>
<p class="titlep"> </p>
<h2 class="subtitle">Anonymity</h2>
</section><section id="TOC">
<nav role="doc-toc">
<h2 id="toc-title">Contents</h2>
<ul>
<li><a href="#/introduction" id="/toc-introduction">Introduction</a></li>
<li><a href="#/sender-anonymity" id="/toc-sender-anonymity">Sender Anonymity</a></li>
<li><a href="#/onion-routing-tor" id="/toc-onion-routing-tor">Onion Routing (Tor)</a></li>
<li><a href="#/attacking-anonymity-systems" id="/toc-attacking-anonymity-systems">Attacking Anonymity Systems</a></li>
</ul>
</nav>
</section>
<section id="source" class="slide level2">
<h2>Source</h2>
<p>This slide set was based, with permission, on one created by Benjamin Kreuter while at the University of Virginia in 2012. He now works for Google, and you can see his work <a href="https://www.youtube.com/watch?v=iViQHHchtbk">here</a> and <a href="https://www.youtube.com/watch?v=ee7oRsDnNNc&t=1239s">here</a>.</p>
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</section>
<section>
<section id="introduction" class="title-slide slide level1 center">
<h1>Introduction</h1>
</section>
<section id="why-anonymity" class="slide level2">
<h2>Why anonymity?</h2>
<ul>
<li>Whenever a big announcement is planned, the White House staff places a big order for pizza from a nearby pizza shop</li>
<li>Journalists begin publishing speculation about the big announcement hours before it is made</li>
<li><strong><em>What went wrong?</em></strong></li>
</ul>
<p>(this is called the <a href="http://www.slate.com/articles/life/food/2016/07/the_pizza_meter_was_a_staple_of_1990s_pop_pseudoscience_we_should_revive.html">Pizza Meter</a>, by the way)</p>
</section>
<section id="why-anonymity-1" class="slide level2">
<h2>Why anonymity?</h2>
<ul>
<li>Suppose you are running a human rights organization in a hostile nation
<ul>
<li>The government is probably watching your communication, so you encrypt your email</li>
</ul></li>
<li>A dissident in a nearby town sends you emails, encrypted using your public key</li>
<li>Suddenly the dissident is arrested and sent to a reeducation camp</li>
<li><strong><em>What went wrong?</em></strong></li>
</ul>
</section>
<section id="why-anonymity-2" class="slide level2">
<h2>Why anonymity?</h2>
<p>Encryption is great for preventing people from reading your messages</p>
<p>It does not prevent people from seeing who you correspond with, which in some cases is more important than the content of that correspondence</p>
</section>
<section id="receiving-messages-anonymously" class="slide level2">
<h2>Receiving Messages Anonymously</h2>
<ul>
<li><em>Receiving</em> a message anonymously is easier than sending a message anonymously</li>
<li>Intelligence agencies have been taking advantage of this for decades, by broadcasting instructions to covert agents using shortwave radio, which has a global range</li>
<li>We can duplicate this online:
<ul>
<li>A message may be sent to a mailing list, posted to Usenet (e.g. in alt.anonymous.messages), uploaded to a blog or wiki, etc.</li>
</ul></li>
</ul>
</section>
<section id="broadcasting-is-not-enough" class="slide level2">
<h2>Broadcasting is not Enough</h2>
<ul>
<li>A medical doctor known for advocating medical marijuana use corresponds with his patients by broadcasting encrypted messages on Usenet and by having them do the same</li>
<li>The DEA raids the doctor’s office, taking his computer and identifying the doctor’s patients</li>
<li><strong><em>What went wrong?</em></strong></li>
</ul>
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</section></section>
<section>
<section id="sender-anonymity" class="title-slide slide level1 center">
<h1>Sender Anonymity</h1>
</section>
<section id="sender-anonymity-1" class="slide level2">
<h2>Sender Anonymity</h2>
<p>Protecting the identity of a <em>sender</em> is more technically challenging</p>
<p>We will not address with situations where the <em>use</em> of encryption or of an anonymity system must be hidden.</p>
</section>
<section id="overview" class="slide level2">
<h2>Overview</h2>
<ul>
<li>Early systems - Penet</li>
<li>Cypherpunks remailers</li>
<li>Some theory</li>
<li>Tor</li>
<li>Attacking anonymity systems</li>
<li>Ethical questions</li>
</ul>
</section>
<section id="should-people-be-required-to-use-their-real-name-online" class="slide level2">
<h2>Should people be required to use their real name online?</h2>
<ul>
<li>In the early 90s, Johan Helsingius created the Penet Remailer as a response to suggestions that people should be required to use their legal names online
<ul>
<li>References: <a href="https://web.archive.org/web/20160429150813/http://waste.informatik.hu-berlin.de/Grassmuck/Texts/remailer.html">1</a> and <a href="https://www.amazon.com/dp/047105318X/">2</a></li>
</ul></li>
</ul>
</section>
<section id="should-people-be-required-to-use-their-real-name-online-1" class="slide level2">
<h2>Should people be required to use their real name online?</h2>
<ul>
<li>To use Penet, send an email requesting a pseudonym</li>
<li>Mail sent to the pseudonym would be forwarded to the user’s real email address</li>
<li>A user could send an email to Penet, and have the message forwarded with their pseudonym in the “From:” field</li>
</ul>
</section>
<section id="getting-a-penet-anon-id" class="slide level2">
<h2>Getting a Penet anon ID</h2>
<div class="sourceCode" id="cb1"><pre class="sourceCode numberSource text number-lines code-with-copy"><code class="sourceCode"><span id="cb1-1"><a href=""></a>From: [email protected]</span>
<span id="cb1-2"><a href=""></a>To: <user questing the ID></span>
<span id="cb1-3"><a href=""></a></span>
<span id="cb1-4"><a href=""></a>You have sent a message using the anonymous contact </span>
<span id="cb1-5"><a href=""></a>service.</span>
<span id="cb1-6"><a href=""></a>You have been allocated the code name an123456.</span>
<span id="cb1-7"><a href=""></a>You can be reached anonymously using the address</span>
<span id="cb1-8"><a href=""></a>[email protected].</span>
<span id="cb1-9"><a href=""></a></span>
<span id="cb1-10"><a href=""></a>If you want to use a nickname, please send a message to</span>
<span id="cb1-11"><a href=""></a>[email protected], with a Subject: field containing </span>
<span id="cb1-12"><a href=""></a>your nickname.</span>
<span id="cb1-13"><a href=""></a></span>
<span id="cb1-14"><a href=""></a>For instructions, send a message to [email protected].</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<p>(not a real anon ID, by the way)</p>
</section>
<section id="the-demise-of-penet" class="slide level2">
<h2>The Demise of Penet</h2>
<p>
</p>
<p>
</p>
<p>What could possibly go wrong?</p>
</section>
<section id="the-demise-of-penet-1" class="slide level2">
<h2>The Demise of Penet</h2>
<ul>
<li>Penet maintained a database mapping pseudonyms to email addresses; a single point of failure!</li>
<li>Numerous requests for specific entries, and for the whole database, had been made while Penet was running -Penet was ultimately shut down after several legal attacks by the Church of Scientology, after secret Scientology material was posted to Usenet through Penet</li>
<li>See the <a href="https://en.wikipedia.org/wiki/Penet_remailer">Wikipedia article on the Penet remailer</a></li>
</ul>
</section>
<section id="after-penet" class="slide level2">
<h2>After Penet</h2>
<p>Lessons learned from Penet:</p>
<ul>
<li>Remailer control messages should be encrypted, so that remailers can be chained. No single remailer should know both the sender and receiver of a message</li>
<li>Records should not be necessary for sending anonymous messages. To receive replies records need to be kept, but should allow for messages to be encrypted and forwarded through other remailers</li>
</ul>
</section>
<section id="after-penet-1" class="slide level2">
<h2>After Penet</h2>
<p>Lessons learned from Penet:</p>
<ul>
<li>Those wishing to compromise remailers may be willing to go to great lengths, using legal or illegal means</li>
</ul>
</section>
<section id="cypherpunks-remailers" class="slide level2">
<h2><a href="https://en.wikipedia.org/wiki/Cypherpunk_anonymous_remailer">Cypherpunks Remailers</a></h2>
<div class="right-float-img" style="zoom:150%">
<p><img data-src="images/anonymity/cypherpunks.jpg"></p>
</div>
<p>After Penet, the next generation of remailers was built using <em>PGP</em>, a popular email encryption program</p>
<p>To use a Cypherpunks remailer, email messages encrypted, then sent to the remailer in the following format, encrypted using the remailer’s public key:</p>
</section>
<section id="cypherpunks-remailers-1" class="slide level2">
<h2>Cypherpunks Remailers</h2>
<p>Cypherpunks remailers have a variety of directives that can be used to improve security:</p>
<ul>
<li>Remailers can be instructed to re-encrypt part of a message using a symmetric cipher; this is used to setting up reply chains for pseudonymous remailers like Penet</li>
<li>Random padding can be added, or messages may be truncated below a certain line</li>
</ul>
</section>
<section id="cypherpunks-remailers-2" class="slide level2">
<h2>Cypherpunks Remailers</h2>
<p>Cypherpunks remailers have a variety of directives that can be used to improve security:</p>
<ul>
<li>Messages can rendered invalid after a certain date, or after being remailed a certain number of times.
<ul>
<li>This helps prevent replay attacks</li>
</ul></li>
<li>The subject line can be encrypted</li>
<li>Random remailer hops can be added</li>
</ul>
</section>
<section id="cypherpunks-remailers-3" class="slide level2">
<h2>Cypherpunks Remailers</h2>
<p>Despite being somewhat ad-hoc, Cypherpunks remailers remain around in some form (see <a href="https://remailer.paranoici.org/">https://remailer.paranoici.org/</a>)</p>
<p>Some remailers provide reliability statistics, by sending test messages through known remailers</p>
<p>Cypherpunks remailers can be used to send messages to email addresses or to Usenet newsgroups</p>
</section>
<section id="anonymity-theory" class="slide level2">
<h2>Anonymity Theory</h2>
<ul>
<li>Cypherpunks remailers work well, but they provide only <em>heuristic</em> guarantees of security
<ul>
<li>In particular, there is no proof that an adversary could not send specially crafted messages through a remailer to break the security model</li>
</ul></li>
<li>David Chaum proposed a more rigorous formulation of security, which imposes stricter requirements than Cypherpunks remailers
<ul>
<li>Chaum’s solution is implemented in more advanced remailers called <em>Mixmaster remailers</em></li>
</ul></li>
</ul>
</section>
<section id="anonymity-theory-1" class="slide level2">
<h2>Anonymity Theory</h2>
<ul>
<li>However, even these remailers do not provide strong security guarantees.</li>
<li>In cryptography research, there is a notion of <em>provable</em> security
<ul>
<li>Showing that breaking a cryptosystem’s security is <em>at least as hard</em> as solving a computationally difficult problem, such as the <em>discrete logarithm problem</em></li>
</ul></li>
<li>Consdier <a href="https://en.wikipedia.org/wiki/Ciphertext_indistinguishability">ciphertext indistinguishability</a>: “an adversary will be unable to distinguish pairs of ciphertexts based on the message they encrypt”</li>
</ul>
</section>
<section id="anonymity-theory-2" class="slide level2">
<h2>Anonymity Theory</h2>
<ul>
<li>It can be shown that if the <a href="https://en.wikipedia.org/wiki/ElGamal_encryption">ElGamal</a> encryption system does not satisfy a given ciphertext indistinguishability, then the <em>discrete logarithm problem</em> is computationally easy
<ul>
<li>ElGamal is based on, and similar in function to, the Diffie-Hellman key exchange</li>
</ul></li>
<li>Since it is widely assumed that the discrete logarithm problem is computationally hard (for good reasons), we can conclude that ElGamal is secure against any chosen plaintext attack</li>
</ul>
</section>
<section id="anonymity-theory-3" class="slide level2">
<h2>Anonymity Theory</h2>
<ul>
<li>Stronger security guarantees can also be proved</li>
<li><em>Adaptive chosen ciphertext</em> attacks allow the adversary to request decryptions of any ciphertext except the challenge, both before and after seeing the challenge</li>
<li>Cryptosystems that are secure against such attacks are known; Cramer-Shoup is an analog of ElGamal with this property</li>
</ul>
</section>
<section id="anonymity-theory-4" class="slide level2">
<h2>Anonymity Theory</h2>
<ul>
<li>We can apply this technique to the analysis of other security systems, including anonymity systems</li>
<li>We need a definition of anonymity that captures our notions about security</li>
</ul>
</section>
<section id="anonymity-theory-notions" class="slide level2">
<h2>Anonymity Theory “Notions”</h2>
<ol type="1">
<li>The adversary might be global - all the messages sent between nodes in the system might be observed</li>
<li>The adversary might be able to take control of some of the nodes, both before and after observing messages (adaptive corruption)</li>
<li>The adversary might send messages through the system, both before and after observing messages</li>
<li>The adversary might be able to choose what messages are sent by honest parties</li>
</ol>
</section>
<section id="anonymity-theory-5" class="slide level2">
<h2>Anonymity Theory</h2>
<ul>
<li>A rigorous definition of security for an anonymity system was given by Abe and Imai in 2003, which meets all of the above criteria</li>
<li>Camenisch and Mityagin in 2006 proposed a system which meets this definition and which can be securely composed with any other protocol</li>
<li>Following another rigorous definition, Danezis and Goldberg in 2008 presented Sphinx, a provably secure remailer that can be integrated with Mixmaster and Cypherpunks remailers</li>
<li>So we can have a secure remailer!</li>
</ul>
</section>
<section id="anonymity-beyond-email" class="slide level2">
<h2>Anonymity Beyond Email</h2>
<ul>
<li>Remailers are great for high-latency communication like email</li>
<li>Can we get low-latency anonymity?</li>
<li>Can we browse the web anonymously?</li>
<li>In 1998, researchers at the US Naval Research Laboratory released a low-latency anonymity system call Tor, which uses onion routing</li>
</ul>
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</section></section>
<section>
<section id="onion-routing-tor" class="title-slide slide level1 center">
<h1>Onion Routing (Tor)</h1>
</section>
<section id="tor" class="slide level2">
<h2>Tor</h2>
<ul>
<li>Tor stands for The Onion Router</li>
<li>Consdier a path to destination S through a network:
<ul>
<li>Y (client) <-> A <-> B <-> C <-> S (server)</li>
<li>A, B, and C are randomly chosen nodes in the Tor network</li>
<li>Each node has a public key <span class="math inline">\(pk_A\)</span>, <span class="math inline">\(pk_S\)</span>, etc.</li>
</ul></li>
<li>We have two functions we will use:
<ul>
<li><span class="math inline">\(enc(pk,X)\)</span>: encrypt <span class="math inline">\(X\)</span> with public key <span class="math inline">\(pk\)</span></li>
<li><span class="math inline">\(sendTo(dest,X)\)</span>: a request to send <span class="math inline">\(X\)</span> to destination <span class="math inline">\(dest\)</span></li>
</ul></li>
</ul>
</section>
<section id="tor-terminology" class="slide level2">
<h2>Tor Terminology</h2>
<ul>
<li>Given path: Y (client) <-> A <-> B <-> C <-> S (server)</li>
<li>A is the <em>entry relay</em> or a <em>bridge</em>
<ul>
<li>These are generally well known and published</li>
</ul></li>
<li>B and C are just <em>relays</em>
<ul>
<li>Some are well known, others are kept secret</li>
</ul></li>
<li>As for S:
<ul>
<li>If the detination is <em>outside</em> of Tor, then it sends the data (via TLS) to the destination, and S is called the <em>exit relay</em></li>
<li>If the destination is <em>inside</em> of Tor, then S is the <em>hidden service</em></li>
</ul></li>
</ul>
</section>
<section id="how-tor-works" class="slide level2">
<h2>How Tor works</h2>
<ul>
<li>Given path: Y (client) <-> A <-> B <-> C <-> S (server)</li>
<li>Given primitives: <span class="math inline">\(enc(pk,X)\)</span> & <span class="math inline">\(sendTo(dest,X)\)</span></li>
<li>To send <span class="math inline">\(p\)</span> to <span class="math inline">\(S\)</span>, we construct:
<ul>
<li><span class="math inline">\(m_1 = enc(pk_S,p)\)</span></li>
<li><span class="math inline">\(m_2 = sendTo(S,m_1)\)</span></li>
<li><span class="math inline">\(m_3 = enc(pk_C,m_2)\)</span></li>
<li><span class="math inline">\(m_4 = sendTo(C,m_3)\)</span></li>
<li><span class="math inline">\(m_5 = enc(pk_B,m_4)\)</span></li>
<li><span class="math inline">\(m_6 = sendTo(B,m_5)\)</span></li>
<li><span class="math inline">\(m_7 = enc(pk_A,m_6)\)</span></li>
</ul></li>
<li><span class="math inline">\(m_7\)</span> is then sent by the client to entry relay <span class="math inline">\(A\)</span></li>
</ul>
</section>
<section id="the-final-message" class="slide level2">
<h2>The final message</h2>
<ul>
<li><span class="math inline">\(m = enc(pk_A,sendTo(B,enc(pk_B,\)</span><br><span class="math inline">\(sendTo(\)</span><span class="math inline">\(C,enc(pk_C,\)</span><br><span class="math inline">\(sendTo(S,enc(pk_S,p)))))))\)</span></li>
<li>Each successive message is encrypted, forming <em>layers</em>
<ul>
<li>Layers like an onion, hence the name <em>onion routing</em></li>
</ul></li>
<li>Note that the final node (<span class="math inline">\(S\)</span>) is the final node <em>inside</em> Tor
<ul>
<li>Either the exit relay or the hidden service</li>
</ul></li>
</ul>
</section>
<section id="tor-overview" class="slide level2">
<h2>Tor overview</h2>
<ul>
<li>Tor can be viewed as a chain of proxy servers, which is periodically changed to make attacks harder</li>
<li>Each Tor connection goes through three (or more) nodes: the entry node, middle node(s), and exit node</li>
<li>To connect to Tor, the client first downloads a list of all Tor nodes from several directory authorities</li>
<li>The nodes used for connections will be selected offline, so that no information about a client’s route will be leaked</li>
</ul>
</section>
<section id="hidden-services" class="slide level2">
<h2>Hidden Services</h2>
<ul>
<li>Tor also provides hidden services
<ul>
<li>This allows a server to be run anonymously</li>
</ul></li>
<li>Each hidden service selects several middle nodes to act as “guards” (or <em>introduction points</em>) which are connected through additional Tor nodes to the hidden service
<ul>
<li>Clients can look up guards for a hidden service in a distributed hash table</li>
<li>Thus, the client has to route to the introduction point, and the introduction point will route to the hidden service</li>
</ul></li>
</ul>
</section>
<section id="the-silk-road" class="slide level2">
<h2>The Silk Road</h2>
<div class="right-float-img img-size-600" style="zoom:150%">
<p><img data-src="images/anonymity/Silk_Road_Marketplace_Item_Screen.jpg"></p>
</div>
<ul>
<li>A Tor hidden serivce at silkroad7rn2puhj.onion
<ul>
<li>Named after the <a href="https://en.wikipedia.org/wiki/Silk_Road">historical trade route of the same name</a></li>
</ul></li>
<li>It sold illegal drugs online</li>
<li>Run by the “Dread Pirate Roberts” (DPR), it was shut down in 2013
<ul>
<li>Others quickly took its place</li>
</ul></li>
</ul>
</section>
<section id="how-was-the-silk-road-busted" class="slide level2">
<h2>How was the Silk Road busted?</h2>
<ul>
<li>Two versions (from <a href="https://en.wikipedia.org/wiki/Silk_Road_%28marketplace%29">Wikipedia</a>)
<ul>
<li>“The FBI has claimed that the real IP address of the Silk Road server was found via data leaked directly from the site’s CAPTCHA”</li>
<li>Security researchers believe that the PHP login page was manipulated to output its server variables, including the IP address</li>
</ul></li>
<li>Ross Ulbricht, alleged to be DPR, was arrested in Oct 2, 2013
<ul>
<li>The FBI siezed about $90 million in bitcoins</li>
<li>He was sentenced to life in prison w/out parole</li>
</ul></li>
</ul>
</section>
<section id="tor-stats" class="slide level2">
<h2>Tor stats</h2>
<ul>
<li>Tor is currently the most popular anonymity system in use, with hundreds of thousands of users</li>
<li>These metrics are as of November 2018 and are from <a href="https://metrics.torproject.org/">https://metrics.torproject.org/</a>:
<ul>
<li>653 entry relays (“bridges”)</li>
<li>6,398 (internal) relays</li>
<li>About 2 million users</li>
<li>107,490 unique onion services
<ul>
<li><a href="https://en.wikipedia.org/wiki/Tor_%28anonymity_network%29#Usage">Some estimates</a> indicate that about half are inactive</li>
</ul></li>
</ul></li>
</ul>
</section>
<section id="how-to-detect-tor" class="slide level2">
<h2>How to detect Tor</h2>
<ul>
<li>Assuming one can monitor a network link…</li>
<li>If TLS encrypted data is sent to a Tor entry node, then one is likely using Tor</li>
<li>Many gov’t’s (including the US) will pay “more” attention to you if it seems you are using Tor</li>
</ul>
</section>
<section id="tor-usage" class="slide level2">
<h2>Tor usage</h2>
<ul>
<li>Tor is often used to defeat national firewalls; an ongoing area of work is disguising a Tor connection as a typical Firefox TLS connection</li>
<li>A common pattern has emerged in such countries: Tor is typically blocked just before big announcements by the government, or immediately following news of rebellions or unrest in other countries</li>
</ul>
</section>
<section id="us-govt-policy-on-tor" class="slide level2">
<h2>US gov’t policy on Tor</h2>
<ul>
<li>Some agencies support it: US state department, NSF, and <a href="https://en.wikipedia.org/wiki/Radio_Free_Asia">Radio Free Asia</a></li>
<li>Some oppose it: NSA, FBI, CIA</li>
</ul>
</section>
<section id="would-you-buy-an-internet-connected-sex-toy" class="slide level2">
<h2>Would you buy an Internet connected sex toy?</h2>
</section>
<section id="would-you-buy-an-internet-connected-sex-toy-1" class="slide level2">
<h2>Would you buy an Internet connected sex toy?</h2>
<ul>
<li>Apparently a lot of people do, but they keep getting hacked
<ul>
<li><a href="https://www.wired.co.uk/article/sex-toy-bluetooth-hacks-security-fix">Wired article on this</a></li>
</ul></li>
<li>Security idea: have the sex toy use Tor</li>
<li>This is a field of study called “onion dildonics”
<ul>
<li>I promise that I did not make that name up…</li>
</ul></li>
<li>While the application is somewhat humorous, the privacy implications involved are very real</li>
<li>Tor has been suggested as the answer to this</li>
</ul>
</section>
<section id="tor-the-benefits" class="slide level2">
<h2>Tor: The Benefits</h2>
<ul>
<li>It allows for “true” anonymity online</li>
<li>It allows for much better privacy than otherwise is available</li>
<li>The gov’t cannot figure out what you are saying or doing
<ul>
<li>(Although they can tell if you are using it)</li>
</ul></li>
</ul>
</section>
<section id="tor-the-drawbacks" class="slide level2">
<h2>Tor: The Drawbacks</h2>
<ul>
<li>This is how evil stuff is propogated online
<ul>
<li>Child pornography, snuff films, torture films, rape videos, etc.</li>
<li>The real stuff, not fake films done by actors for entertainment</li>
</ul></li>
</ul>
</section>
<section id="tor-ethics" class="slide level2">
<h2>Tor: Ethics</h2>
<ul>
<li>Considering the benefits and drawbacks, is it ethical to use Tor?</li>
</ul>
</section>
<section id="tor-ethics-1" class="slide level2">
<h2>Tor: Ethics</h2>
<ul>
<li>Considering the benefits and drawbacks, is it ethical to use Tor?</li>
<li>If you are using for ethical means (privacy, for example), then yes
<ul>
<li>Just because a technology <em>can</em> be used for illegal means does not automatically make that technology unethical</li>
<li>If that were the case, then all of computers would be illegal</li>
</ul></li>
</ul>
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</section></section>
<section>
<section id="attacking-anonymity-systems" class="title-slide slide level1 center">
<h1>Attacking Anonymity Systems</h1>
</section>
<section id="attacking-remailers" class="slide level2">
<h2>Attacking Remailers</h2>
<ul>
<li>Global eavesdropping: watching all traffic through all remailers, and following one message
<ul>
<li>This can be thwarted using random delays, random padding, and message reordering</li>
</ul></li>
</ul>
</section>
<section id="attacking-remailers-1" class="slide level2">
<h2>Attacking Remailers</h2>
<ul>
<li>Replay attacks: sending the same message through a Remailer, and seeing what comes out
<ul>
<li>This can be thwarted with maximum date headers, assuming PGP is non-malleable (which could be untrue), and does not work against Mixmaster remailers</li>
</ul></li>
</ul>
</section>
<section id="attacking-remailers-2" class="slide level2">
<h2>Attacking Remailers</h2>
<ul>
<li>Attacking specific remailers: if the adversary has some remailers under his control, he can flood other remailers in an attempt to prevent them from being used</li>
</ul>
</section>
<section id="attacking-remailers-3" class="slide level2">
<h2>Attacking Remailers</h2>
<ul>
<li>Spamming attacks: If a pseudonym delivers messages to an email address, through a chain of remailers, the chain could be traced by an attacker who sends many “spam” messages to the pseudonym
<ul>
<li>This can be thwarted by having messages delivered to a Usenet newsgroup or by limiting how many messages can be sent before the remailer chain is changed</li>
</ul></li>
</ul>
</section>
<section id="attacking-remailers-4" class="slide level2">
<h2>Attacking Remailers</h2>
<ul>
<li>Mail loops: A pseudonym may be configured to have replies sent through several remailer chains; this could be used to create loops that exponentially increase the load on a remailer
<ul>
<li>Typically, the amount of mail a pseudonym can receive in a given day before being disabled is deliberately limited</li>
</ul></li>
</ul>
</section>
<section id="attacking-tor" class="slide level2">
<h2>Attacking Tor</h2>
<ul>
<li>Global eavesdropping: Tor does not have random delays or padding, so a global eavesdropper can defeat Tor</li>
</ul>
</section>
<section id="attacking-tor-1" class="slide level2">
<h2>Attacking Tor</h2>
<ul>
<li>Fingerprinting: a local eavesdropper can collect information about latency patterns for specific systems accessed through Tor, and check for such patterns in a target connection
<ul>
<li>This is particularly bad in cases where some information about a person’s identity is leaked; for example, forum posts that use regional spellings or phrases</li>
</ul></li>
</ul>
</section>
<section id="attacking-anonymity-systems-1" class="slide level2">
<h2>Attacking Anonymity Systems</h2>
<ul>
<li>Malicious exit nodes: if end-to-end encryption is not used, a malicious exit can sniff usernames, passwords, and other information</li>
</ul>
</section>
<section id="ethical-questions" class="slide level2">
<h2>Ethical Questions</h2>
<ul>
<li>Should anonymity systems even be deployed?
<ul>
<li>Criminals, terrorists, etc. may use anonymity systems to avoid detection or prosecution</li>
<li>Anonymity systems have been used for harassing people and by child predators</li>
<li>Human rights groups, political dissidents, law enforcement agencies, etc. also use anonymity systems</li>
<li>In some cases, anonymity systems could save lives</li>
</ul></li>
</ul>
</section>
<section id="ethical-questions-1" class="slide level2">
<h2>Ethical Questions</h2>
<ul>
<li>Should attacks on anonymity systems be published?
<ul>
<li>Law enforcement agencies may be given an advantage with unpublished attacks</li>
<li>Such attacks are likely to be discovered and kept secret by hostile governments, criminal hackers, etc.</li>
</ul></li>
</ul>
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