add blogpost explaining the scavenger hunt (#270)

Signed-off-by: Christine Dodrill <me@christine.website>

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+---
+title: Scavenger Hunt Solution
+date: 2020-11-25
+tags:
+ - ctf
+ - wasm
+ - steganography
+ - stenography
+---
+
+# Scavenger Hunt Solution
+
+On November 22, I sent a
+[tweet](https://twitter.com/theprincessxena/status/1330532765482311687) that
+contained the following text:
+
+```
+#467662 #207768 #7A7A6C #6B2061 #6F6C20 #6D7079 
+#7A6120 #616C7A #612E20 #5A6C6C #206F61 #61773A 
+#2F2F6A #6C6168 #6A6C68 #752E6A #736269 #2F6462 
+#796675 #612E6E #747020 #6D7679 #207476 #796C20 
+#70756D #767974 #686170 #76752E
+```
+
+This was actually the first part of a scavenger hunt/mini CTF that I had set up
+in order to see who went down the rabbit hole to solve it. I've had nearly a
+dozen people report back to me telling that they solved all of the puzzles and
+nearly all of them said they had a lot of fun. Here's how to solve each of the
+layers of the solution and how I created them.
+
+## Layer 1
+
+The first layer was that encoded tweet. If you notice, everything in it is
+formatted as HTML color codes. HTML color codes just so happen to be encoded in
+hexadecimal. Looking at the codes you can see `20` come up a lot, which happens
+to be the hex-encoded symbol for the spacebar. So, let's turn this into a
+continuous hex string with `s/#//g` and `s/ //g`:
+
+[If you've seen a `%20` in a URL before, that is the URL encoded form of the
+spacebar!](conversation://Mara/hacker)
+
+```
+4676622077687A7A6C6B20616F6C206D7079
+7A6120616C7A612E205A6C6C206F6161773A
+2F2F6A6C61686A6C68752E6A7362692F6462
+796675612E6E7470206D7679207476796C20
+70756D76797468617076752E
+```
+
+And then turn it into an ASCII string:
+
+> Fvb whzzlk aol mpyza alza. Zll oaaw://jlahjlhu.jsbi/dbyfua.ntp mvy tvyl pumvythapvu.
+
+[Wait, what? this doesn't look like much of anything...wait, look at the
+`oaaw://`. Could that be `http://`?](conversation://Mara/hmm)
+
+Indeed it is my perceptive shark friend! Let's decode the rest of the string
+using the [Caeser Cipher](https://en.wikipedia.org/wiki/Caesar_cipher):
+
+> You passed the first test. See http://cetacean.club/wurynt.gmi for more information.
+
+Now we're onto something!
+
+## Layer 2
+
+Opening http://cetacean.club/wurynt.gmi we see the following:
+
+> wurynt
+> 
+> a father of modern computing, <br />
+> rejected by his kin, <br />
+> for an unintentional sin, <br />
+> creator of a machine to break <br />
+> the cipher that this message is encoded in
+> 
+> bq cr di ej kw mt os px uz gh
+>
+> VI 1 1
+> I 17 1
+> III 12 1
+> 
+> qghja xmbzc fmqsb vcpzc zosah tmmho whyph lvnjj mpdkf gbsjl tnxqf ktqia mwogp
+> eidny awoxj ggjqz mbrcm tkmyd fogzt sqkga udmbw nmkhp jppqs xerqq gdsle zfxmq
+> yfdfj kuauk nefdc jkwrs cirut wevji pumqt hrxjr sfioj nbcrc nvxny vrphc r
+>
+> Correction for the last bit
+> 
+> gilmb egdcr sowab igtyq pbzgv gmlsq udftc mzhqz exbmx zaxth isghc hukhc zlrrk
+> cixhb isokt vftwy rfdyl qenxa nljca kyoej wnbpf uprgc igywv qzuud hrxzw gnhuz
+> kclku hefzk xtdpk tfjzu byfyi sqmel gweou acwsi ptpwv drhor ahcqd kpzde lguqt
+> wutvk nqprx gmiad dfdcm dpiwb twegt hjzdf vbkwa qskmf osjtk tcxle mkbnv iqdbe
+> oejsx lgqc
+
+[Hmm, "a father of computing", "rejected by his kin", "an unintentional sin",
+"creator of a machine to break a cipher" could that mean Alan Turing? He made
+something to break the Enigma cipher and was rejected by the British government
+for being gay right?](conversation://Mara/hmm)
+
+Indeed. Let's punch these settings into an [online enigma
+machine](https://cryptii.com/pipes/enigma-machine) and see what we get:
+
+```
+congr adula tions forfi gurin goutt hisen igmao famys teryy ouhav egott enfar
+thert hanan yonee lseha sbefo rehel pmebr eakfr eefol lowth ewhit erabb ittom
+araht tpyvz vgjiu ztkhf uhvjq roybx dswzz caiaq kgesk hutvx iplwa donio n
+
+httpc olons lashs lashw hyvec torze dgamm ajayi ndigo ultra zedfi vetan gokil
+ohalo fineu ltrah alove ctorj ayqui etrho omega yotta betax raysi xdonu tseve
+nsupe rwhyz edzed canad aasia indig oasia twoqu ietki logam maeps ilons uperk
+iloha loult rafou rtang ovect orsev ensix xrayi ndigo place limaw hyasi adelt
+adoto nion
+```
+
+And here is where I messed up with this challenge. Enigma doesn't handle
+numbers. It was designed to encode the 26 letters of the Latin alphabet. If you
+look at the last bit of the output you can see `onio n` and `o nion`. This
+points you to a [Tor hidden
+service](https://www.linuxjournal.com/content/tor-hidden-services), but because
+I messed this up the two hints point you at slightly wrong onion addresses (tor
+hidden service addresses usually have numbers in them). Once I realized this, I
+made a correction that just gives away the solution so people could move on to
+the next step.
+
+Onwards to
+http://yvzvgjiuz5tkhfuhvjqroybx6d7swzzcaia2qkgeskhu4tv76xiplwad.onion/!
+
+## Layer 3
+
+Open your [tor browser](https://www.torproject.org/download/) and punch in the
+onion URL. You should get a page that looks like this:
+
+![Mara's
+Realm](https://cdn.christine.website/file/christine-static/blog/Screenshot_20201125_101515.png)
+
+This shows some confusing combinations of letters and some hexadecimal text.
+We'll get back to the hexadecimal text in a moment, but let's take a closer look
+at the letters. There is a hint here to search the plover dictionary.
+[Plover](http://www.openstenoproject.org/) is a tool that allows hobbyists to
+learn [stenography](https://en.wikipedia.org/wiki/Stenotype) to type at the rate
+of human speech. My moonlander has a layer for typing out stenography strokes,
+so let's enable it and type them out:
+
+> Follow the white rabbit
+> 
+> Go to/test. w a s m
+
+Which we can reinterpret as:
+
+> Follow the white rabbit
+> 
+> Go to /test.wasm
+
+[The joke here is that many people seem to get stenography and steganography
+confused, so that's why there's stenography in this steganography
+challenge!](conversation://Mara/hacker)
+
+Going to /test.wasm we get a WebAssembly download. I've uploaded a copy to my
+blog's CDN
+[here](https://cdn.christine.website/file/christine-static/blog/test.wasm).
+
+## Layer 4
+
+Going back to that hexadecimal text from above, we see that it says this:
+
+> go get tulpa.dev/cadey/hlang
+
+This points to the source repo of [hlang](https://h.christine.website), which is
+a satirical "programming language" that can only print the letter `h` (or the
+lojbanic h `'` for that sweet sweet internationalisation cred). Something odd
+about hlang is that it uses [WebAssembly](https://webassembly.org/) to execute
+all programs written in it (this helps it reach its "no sandboxing required" and
+"zero* dependencies" goals).
+
+Let's decompile this WebAssembly file with
+[`wasm2wat`](https://webassembly.github.io/wabt/doc/wasm2wat.1.html)
+
+```console
+$ wasm2wat /data/test.wasm
+<output too big, see https://git.io/Jkyli>
+```
+
+Looking at the decompilation we can see that it imports a host function `h.h` as
+the hlang documentation suggests and then constantly calls it a bunch of times:
+
+```lisp
+(module
+  (type (;0;) (func (param i32)))
+  (type (;1;) (func))
+  (import "h" "h" (func (;0;) (type 0)))
+  (func (;1;) (type 1)
+    i32.const 121
+    call 0
+    i32.const 111
+    call 0
+    i32.const 117
+    call 0
+  ; ...
+```
+
+There's a lot of `32` in the output. `32` is the base 10 version of `0x20`,
+which is the space character in ASCII. Let's try to reformat the numbers to
+ascii characters and see what we get:
+
+> you made it, this is the end of the line however. writing all of this up takes
+> a lot of time. if you made it this far, email me@christine.website to get your
+> name entered into the hall of heroes. be well.
+
+## How I Implemented This
+
+Each layer was designed independently and then I started building them together
+later. 
+
+One of the first steps was to create the website for Mara's Realm. I started by
+writing out all of the prose into a file called `index.md` and then I ran
+[sw](https://github.com/jroimartin/sw) using [Pandoc](https://pandoc.org/) for
+markdown conversion.
+
+Then I created the WebAssembly binary by locally hacking a copy of hlang to
+allow arbitrary strings. I stuck it in the source directory for the website and
+told `sw` to not try and render it as markdown.
+
+Once I had the HTML source, I copied it to a machine on my network at
+`/srv/http/marahunt` using this command:
+
+```console
+$ rsync \
+    -avz \
+    site.static/ \
+    root@192.168.0.127:/srv/http/marahunt
+```
+
+And then I created a tor hidden service using the
+[services.tor.hiddenServices](https://search.nixos.org/options?channel=20.09&from=0&size=30&sort=relevance&query=services.tor.hiddenServices)
+options:
+
+```nix
+services.tor = {
+  enable = true;
+
+  hiddenServices = {
+    "hunt" = {
+      name = "hunt";
+      version = 3;
+      map = [{
+        port = 80;
+        toPort = 80;
+      }];
+    };
+  };
+};
+```
+
+Once I pushed this config to that server, I grabbed the hostname from
+`/var/lib/tor/onion/hunt/hostname` and set up an nginx virtualhost:
+
+```nix
+services.nginx = {
+  virtualHosts."yvzvgjiuz5tkhfuhvjqroybx6d7swzzcaia2qkgeskhu4tv76xiplwad.onion" =
+    {
+      root = "/srv/http/marahunt";
+    };
+};
+```
+
+And then I pushed the config again and tested it with curl:
+
+```console
+$ curl -H "Host: yvzvgjiuz5tkhfuhvjqroybx6d7swzzcaia2qkgeskhu4tv76xiplwad.onion" http://127.0.0.1 | grep title
+  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
+                                 Dload  Upload   Total   Spent    Left  Speed
+100  3043  100  3043    0     0  2971k      0 --:--:-- --:--:-- --:--:-- 2971k
+<title>Mara's Realm</title>
+.headerSubtitle { font-size: 0.6em; font-weight: normal; margin-left: 1em; }
+<a href="index.html">Mara's Realm</a> <span class="headerSubtitle">sh0rk in the cloud</span>
+```
+
+Once I was satisfied with the HTML, I opened up an enigma encoder and started
+writing out the message congradulating the user for figuring out "this enigma of
+a mystery". I also included the onion URL (with the above mistake) in that
+message.
+
+Then I started writing the wurynt page on my
+[gemini](https://gemini.circumlunar.space/) server. wurynt was coined by blindly
+pressing 6 keys on my keyboard. I added a little poem about Alan Turing to give
+a hint that this was an enigma cipher and then copied the Enigma settings on the
+page just in case. It turned out that I was using the default settings for the
+[Cryptee Enigma simulator](https://cryptii.com/pipes/enigma-machine), so this
+was not needed; however it was probably better to include them regardless.
+
+This is where I messed up as I mentioned earlier. Once I realized my mistake in
+trying to encode the onion address twice, I decided it would be best to just
+give away the answer on the page, so I added the correct onion URL to the end of
+the enigma message so that it wouldn't break flow for people. 
+
+The final part was to write and encode the message that I would tweet out. I
+opened a scratch buffer and wrote out the "You passed the first test" line and
+then encoded it using the ceasar cipher and encoded the result of that into hex.
+After a lot of rejiggering and rewriting to make it have a multiple of 3
+characters of text, I reformatted it as HTML color codes and tweeted it without
+context.
+
+## Feedback I Got
+
+Some of the emails and twitter DM's I got had some useful and amusing feedback.
+Here's some of my favorites:
+
+> my favourite part was the opportunity to go down different various rabbit
+> holes (I got to learn about stenography and WASM, which I'd never looked
+> into!)
+
+> I want to sleep. It's 2 AM here, but a friend sent me the link an hour ago and
+> I'm a cat, so the curiosity killed me.
+
+> That was a fun little game. Thanks for putting it together.
+
+> oh *noooo* this is going to nerd snipe me
+
+> I'm amused that you left the online enigma emulator on default settings.
+
+> I swear to god I'm gonna beach your orca ass
+
+## Improvements For Next Time
+
+Next time I'd like to try and branch out from just using ascii. I'd like to
+throw other encodings into the game (maybe even have a stage written in EBCDIC
+formatted Esperanto or something crazy like that). I was also considering having
+some public/private key crypto in the mix to stretch people's skillsets.
+
+Something I will definitely do next time is make sure that all of the layers are
+solveable. I really messed up with the enigma step and I had to unblock people
+by DMing them the answer. Always make sure your puzzles can be solved.
+
+## Hall of Heroes
+
+(in no particular order)
+
+- Saphire Lattice
+- Open Skies
+- Tramoline
+- AstroSnail
+- Dominika
+- pbardera
+- Max Hollman
+- Vojtěch
+- [object Object]
+- Bytewave
+
+Thank you for solving this! I'm happy this turned out so successfully. More to
+come in the future.
+
+🙂