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DEF CON 27 T-Shirt Puzzle, EFF, Lindsay Oliver and Sydney Young, DEF CON 27


  • DEF CON 27 T-Shirt Puzzle, EFF, Lindsay Oliver and Sydney Young, DEF CON 27


    Originally posted by URL1
    By Lindsay Oliver and Sydney Young
    September 6, 2019

    At Hacker Summer Camp 2019, EFF unveiled our 10th-annual limited edition member shirt—available only during the three-day event, and inspired by the DEF CON theme of Technology’s Promise: “a break from the dystopian imagery into a major-key, blue-sky thoughtscape, full of color and light...a future where we have tamed some of the more intractable problems that plague us in the present, where technology supports and inspires instead of controlling and surveilling.” We took cues from the DEF CON 27 Theme Guide, an illustrated ePub detailing thought exercises, media that inspired the theme, and color/style breakdowns. The theme was heavily influenced by the French comic artist Moebius’ piece entitled Alice, a piece that envisions “a future where tech lives up to our highest hopes.”

    Shirt Design

    EFF’s shirt design is an homage to Moebius, including artwork of a user in a digital future where the downsides of technology have been overcome. She's got a flying machine that is so efficient that it doesn't require her attention; she's got a vintage laptop from the early 21st century that still works thanks to the interoperability of her systems; she can communicate freely, using archaic Morse code, thanks to strong encryption on all of her devices; and of course, she has the ability to change her hair color at will.

    EFF Contest TeeShirt Front

    As in previous years, we’ve included a secret puzzle built into the design of our exclusive member shirt as a special thanks for the clever, curious EFFers who support our work. Read on for a breakdown of the puzzle design and a walkthrough of the puzzle elements. Or, try to solve it yourself! The puzzle can be found at and will be available through September 30th. After the 30th, the puzzle can be found on the Internet Archive’s Wayback Machine.

    Puzzle Design

    We established a technological utopia in our shirt design, and used only one rule to create a fantasy world map of this future: draw like Moebius. With this rule in mind, we wondered - what was under the clouds in the shirt design? Where would this user park her flying machine? We gathered reference materials to inspire us, and studied Le Monde d'Edena to capture Moebius’ distinct architectural and landscape style. We wanted the fantasy map to draw players into the world, where they would get lost in the tiny paths and buildings of this utopian civilization, eventually finding doors and hidden passages to the elements of the puzzle.

    DC27 EFF TeeShirt Contest map

    Puzzle Walkthrough

    Players access the puzzle via the morse code URL on the screen of the intrepid user in our shirt design (. ..-. ..-. .-.-.- --- .-. --. -..-. ... .... .-.). After arriving on the website, mousing over the map reveals glowing links in four different locations. The tower holds the final goal, which can only be deciphered after solving the other three puzzles. We decided to make progression through the puzzle non-linear this year in order to facilitate collaboration, and to give solvers time to do other DEF CON activities in between working on the EFF puzzle.

    DC27 EFF TeeShirt contest morse code


    The “first” puzzle can be found by hovering over the entrance to the palace. The page displays a knitting pattern in chart form. Knitting was chosen as a theme due to the history of women using knit fabrics for “steganography”—to hold concealed messages in times of war, particularly World War I. We also wanted to highlight skill sets not often represented in the cybersecurity space—someone familiar with knitting can immediately recognize something wrong with this pattern. There are entire rows of open circles, the symbol for a “yarn over” (skipping a stitch to create a hole), which doesn’t make sense. Inspecting the pattern reveals a hint, however: “the yarn overs are blanks”. Here are some examples of common patterns—you can compare to see the difference.

    Click image for larger version

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    If you aren’t familiar with knitting, searching “yarn over” and identifying the symbol is the first step to solving this puzzle. The next is recognizing that the page title “SOS” is hinting at more morse code. Looking at the image, there are three different kinds of rows: all knits (blank squares), all purls (filled circles), and all yarn overs. We already know that the yarn overs are blanks from the hint, so that means trying the pattern in two ways: one with the knits as dots, and one as dashes. The correct method is converting knits to dots, which gives the morse code string “.-- .- -. -.. . .-.” which translates to “wander”.

    “ASCII” Art

    The next puzzle’s page is a throwback to an older Internet era, and is located at the docks tunnel. The page contains (mostly) ASCII art, like the following header that was used in EFF’s EFFector mailings (if you haven’t signed up to receive them, you can do so here):

    DC27 EFF TeeShirt Contest ASCII Art

    There are a few different ways to identify where the puzzle is on this page: noticing that the whitespace is off in some of the images, such as the computer, or by taking a closer look at the characters in the pieces themselves. Looking at the character codes, the non-ASCII character U+2800, a braille space, can be found in place of a standard ASCII space 32. A hint in the page reads: “the distribution doesn’t matter”— clueing the solver into the idea that the order of the braille spaces within the art doesn’t hold the solution. Using a script to count the occurrences of U+2800 in each art piece gives the following: ”99 101 112 104 97 108 111 112 111 100”, which are ASCII codepoints for “cephalopod”.

    If you’re curious, check out the script used to encode the braille. You can count the characters with the following line of ruby, where the text is a single piece of art:

    The third puzzle, found in the entrance to the temple, consists of this image:

    DC27 EFF TeeShirt Contest Syzygy

    The first hint towards solving this puzzle is in the URL: “5y2y6y” is “leetcode” for “syzygy”, which is a phenomenon where many celestial bodies (at least three) are collinear in the same gravitational system. The image, keeping with the theme of exploration, shows an imagined system of planets. The answer to the puzzle comes from the first number of rotation steps where the planets will all align under the arrow. There are a number of ways to find this number. The number is small enough that you can write a program to brute force the answer. Or, since the periods of the planets are relatively prime, you can use the Chinese remainder theorem. The first full syzygy of this planetary setup is at step 74800, or leetcode for “taboo”.

    Final Puzzle

    The last puzzle, located at the top of the tower, simply displays:

    DC27 EFF TeeShirt Contest Final Puzzle

    Inspecting the page gives the hint “O(ne) T(rue) P(airing)”, a reference to the one time pad cipher, a relatively old message encryption technique that is difficult to crack as long as the key is random, as long or longer than the plaintext, never reused, and kept secret. A tool like this one can be used to decrypt the text, or the adventurous can read about one time pads and try their hand at translating it themselves. The key to this one time pad is “wandercephalopodtaboo”, a combination of the answers from the three other puzzles. Using this key to decrypt the ciphertext translates it from “oerbslutpjenclprr” to “seeyouspacecowboy”, marking the completion of the puzzle!


    The winners of this year’s puzzle are @aaronsteimle, @_pseudoku, and @0xCryptoK! Their team members also solved our 2013, 2015, 2017, and 2018 DEF CON shirt puzzles.

    DC27 EFF TeeShirt Puzzle Contest Winners

    Thank you to everyone who came by the booth to say hello, donated, and played through our puzzle! Creating this interactive art for our supporters is one of the highlights of our year, and we could not do it without you. If you’d like to support our work, consider becoming a member—and don’t forget to stop by the booth next year.

    Until next time: “See you, space cowboy.”
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