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