# You have prepared. You are determined. You approach the door

Hints:

You don't need any hints, they are littered throughout the images everywhere, and I'm not giving you any more. :)

Ok, I will perhaps assist in framing things a little... This is actually a deceptively simple puzzle (though, simple $\ne$ easy). It isn't multiple layers deep, even if it may appear that way. In fact, there's really only a single puzzle to be solved here, and I believe it's actually doable with information from only three of the images. Most of the rest are hints and pointers to make your life easier, but also to distract a little. Part of the challenge is in filtering the truly necessary information from the noise, and in taking the lessons learned from the hints and applying them to the actual puzzle.

I'll just add one last bit of extra information (which you shouldn't take as a hint, so much as a clarification, for when you get a certain distance in): The security panel's circuitry contains a paradox prevention system...

• Absolutely NOT, Alconja. We need more content like this. :) (I was planning on doing something very similar, myself, soon. =D) Apr 28 '16 at 5:15
• Oh, and if you're viewing on mobile, you might want to click the "full site" link way down the bottom of the page (if using the mobile app, go More => Open in browser, first). Won't impact the solvability, but will just render the images as intended. Apr 28 '16 at 6:37
• Man, you got me! (You lower your standards and decide to try cheating. You are chastised by the puzzle creator.) Apr 28 '16 at 9:46
• @GentlePurpleRain - Thanks. :) And yes, all hand/mouse drawn. Behind the scenes trivia: I was originally going to use a more photorealistic style, but the line height in the site css forces a white space between the rows of images, so I went pixel art to hide it as mortar between the bricks (if that makes sense). Apr 28 '16 at 16:41
• At times like this, I wish a bounty could be awarded to a question.
– user20
Apr 29 '16 at 6:23

After a period of thought, you approach the door triumphantly in order to type in

2369

as the keycode.

As you do so, you recall the reasoning that led you to this conclusion. Putting together the torn sticker, you saw a number of strange symbols in a gridlike shape. Fortunately for you, a calling card was left on the scene, describing the working mechanism of the locking machine. This struck you as a rather odd security practice, but you were not going to look a gift horse in the mouth.

This indicates that some rays should be traced from some starting points, turning, splitting and stopping according to some rules. You wondered what these rules could be, and reached the conclusion that the strange symbols were surely involved.

The grid had a number of those symbols, but after analyzing all of the available information, the meaning of each slowly became clear.

The easiest one to determine was #, thanks to the help of a previous unworthy puzzler who left his note on the floor. He might have failed in his mission, but you were sure you wouldn't do the same.

The image indicates that a ray incident to the # symbol splits into 3 different rays, one in each direction.

Following that, you remembered another odd piece of paper you had found. > and < didn't take long to fall.

After tracing the paths between the numbers listed, you realize that the paths are perfectly described on the right if the symbols > and < indicate right and left turns, respectively.

The writing on the wall seemed out of place. You thought maybe the placement of the @ symbol was important.

If nothing goes through the @, then you reason it should be a ray blocker of some sort.

The lowercase letters seemed impossible to crack. As a desperate attempt, you look through the peephole, when suddenly it opens to reveal someone looking back at you. Despite nearly dying of a heart attack, you manage to recall some very important schematics inside the room...

You notice that the colors in the drawing are blue, cyan, green, magenta, red and yellow, which have a 1-to-1 correspondence with the lowercase letters in the grid: bcgmry. The bottom picture, coupled with the fact that there are two of each of those letters in the grid, suggested those letters should act as portals, teleporting rays from one point of the grid to the other.

But you were clueless as to how any of this would precisely help you. Even if you figured out the inner workings of the system, how would that possibly help with getting in the door? You go back to the note on the ground...

You thought this could mean there is an input-output relationship between the entered code and what the display shows. Thanks to your fiddling with the terminal earlier, you already knew another input-output pair right off the bat: 0001 = DONTGUESS. You recall an interesting line you saw earlier...

It would make a lot of sense if the display produced the word "ENIGMATIC" when the right sequence was pressed. You now noticed that all the letters necessary to spell ENTERPASSCODE, DONTGUESS and ENIGMATIC were present in the grid, so the words were likely being formed by some interaction between the rays and these letters.

The numbers were still unaccounted for. But with your previous guesses, it only made sense that...

the numbers you typed into the machine were being used as starting points for the raycasting. But there were 4 spaces for numbers, so how could this relate to the points? Would that be related to this part of the note on the ground?

You remember the ramblings of your friend @f'' about combinatorics, and how those numbers represented the number of ways to pick 4 digits with order, 4 distinct digits with order, 4 digits without order and 4 distinct digits without order. You never thought any of that would ever be useful, yet here you are. This clued you to the fact that the order of the digits in the password does not matter: pressing the 0 button causes rays to be shot from all zeros in the grid.

All pieces had nearly fallen into place. But you heard beforehand that most puzzlers that dared to open this door were thwarted by a single symbol. Surely enough, you only had a single symbol left: %, and it was proving to be quite the tricky beast. Maybe...

The previous puzzler's notes suggest % is a line shy from being an X, which indicates blocking of some sort. In its initial state, % is open, but whenever one ray passes through this square, it becomes a blocker for further rays. In conclusion, if two or more rays hit this square, they are stopped on their tracks, but a single ray should be able to make it out.

At this point, all of it was purely conjecture. But remembering you had two output pairs, did they confirm your theories? You had to test it to find out.

What happens when rays from all zeros are cast?

You read the uppercase letters crossed by the rays from top to bottom, left to right: "ENTERPASSCODE". You must be on to something! The next step is to try it out with 0001:

You noticed the pink square is a paradox, because letting a ray through it would allow it to loop around to the pink square, blocking itself. You then assumed whoever engineered the system dealt with this somehow, possibly by blocking the ray outright. Making that assumption, the uppercase letters form "DONTGUESS"! Couldn't be a coincidence, could it?

All that was left was figuring out the combination to open the door. By using some process of elimination to quickly weed out numbers that couldn't be present in the final passcode, you reached your most likely candidate.

Most of the numbers caused the rays to immediately pass through letters not in ENIGMATIC. In fact, the only 4 numbers you saw that did not were 2,3,6 and 9. What happens when you use these 4 as starting points?

You read the crossed letters: ENIGMATIC!

Were you finally worthy? There's only one way to find out. You reach for the keypad...

• As you check your logic you realise... X or %?, XOR %... Of course! The % is effectively an exclusive or gate. You punch in the code, and the door sides open. Your worth proven, you step inside and hear a voice. "Welcome ffao. We've been expecting you... Help yourself to cake." May 4 '16 at 8:12
• @BmyGuest I can't draw those beautiful images, but I thought my answer had to at least try to fit the quality of this fantastic puzzle :)
– ffao
May 4 '16 at 8:18
• Oh, and finally, well done to all the other contributors! Another group effort (with an explicit shout out to f", who, for the second of my puzzles in a row, contributed behind the scenes, in comments, etc with almost 100% accuracy) May 4 '16 at 8:25
• Ok, just one more comment... Forgot to add this when I accepted yesterday, but here's a javascript implementation of the security system for anyone interested (don't mind the hackily slapped together code) May 5 '16 at 0:02
• @ffao The pink square is an example of the paradox prevention system mentioned in the question. May 6 '16 at 7:26

Compilation of any findings that may be of importance. It's a community wiki, feel free to contribute.

What the images contain.

1-1

Number grid puzzle

It contains the numbers 0-9, so maybe related to the keypad? Refer to 2012campion's answer for the complete note. It contains the words "The numbers don't lie. Follow?" Are we supposed to follow through the path denoted by the numbers on the right? There are 5 lines, maybe the transition from each line gives a hint to each of the 4 digits of the keycode? Translating < by "left-turn" and > by "right-turn" seems to match five sequences of numbers. It could mean that these right and left turns are directions on the map.

(@feelinferrety) Possibly, you would do well to note which direction you must turn between each < and > to construct the sequence that follows and pull that into another answer. The directions according to a compass rose are as follows. Line 1: 32 w<s 49 Line 2: 0 e<n 8 n<w 54 w>n 1 Line 3: 9 e<n 72 Line 4: 12 e>s 5 s>w 76 Line 5: 87 w<s 9 (@gcampbell) The half from the trash bag could be a trap: if you take the < and > signs as meaning greater-than/less-than, 32 < 49 is true, but 87 < 9 is false. Also note different font on two halves of paper and the phrase "numbers don't lie".

1-2

Brick wall. Most likely nothing.

1-3

The passcode from the keypad might be of relevance here. Maybe the missing part on the right isn't important, but the grid on the left is. I think the grid here paves the way for translating the letter grid in 2-1. My guess is the grid is a labyrinth that will guide us through the letters in 2-1. The two squares could represent starting and ending points.
Update (credits to f"): "Maybe # gives out lines in all four directions, while % blocks them. < and > could make the lines bend."

Update: the passcode supposed to be found with the 4 digits could be ENIGMATIC.

2-1

It seems the flow is 4-digit code (input) into letter sequence (function) into passcode (output). This input/output relationship is reinforced from the wording underneath and also from the hint at 4-3.

7EN%E< 39 c
0% 2%%D14O>
4E%6#1%gE7
5b%83Nc8>@#
% %#53 @I%
rTyGy0>M% U
#%719%E>AM<
RPA% S Sr2m
bT%mT4%>C%6
9g6% O 5 D%
<0>#2@>IE8C

The hints from 4-3 also imply that % = X and the spaces don't matter. Collapsing the whole sequence into one line gives:

7ENXE<39c0X2XXD14O>4EX6#1XgE75bX83Nc8>@#XX#53@IXrTyGy0>MXU#X719XE>AM<RPAXSSr2mbTXmT4X>CX69g6XO5DX<0>#2@>IE8C

The following characters appear at least once in this sequence: # 0 1 2 3 4 5 6 7 8 9 < > @ A C D E G I M N O P R S T U X b c g m r y. It's noteworthy that we get all the numbers 0-9, the symbols >, <, # and @. It is likely the capital letters are relevant for finding the passcode, while the lowercase letters form the colours blue, cyan, green, magenta, red, yellow. Credits to f" for finding this. I believe the colours are a link to the hint from 2-2, where we're supposed to make the link the portals imply wrapping around for the string.

From the string above, I noticed that if we start from the beginning, we can find the letters ENTERPASSCODE in one pass. We can also form NOGUESSING, but it requires wrapping around. Maybe understanding why 0000 gives ENTERPASSCODE and 0001 gives NOGUESSING will tell the four digits that provide ENIGMATIC.
With that said, I believe the 2D structure of the grid is important and we simply have to ignore the blank spaces if we land on them during our navigation. f" and Wesley have pointed out it could represent a 2D programming language with @ representing a no-op and X termination.

Update (Reti43): Maybe we're supposed to overlay the 1-3 grid over here and then only move along the lines. In that case, the two squares in the 1-3 grid could be the portals, which would connect travelling between the two unconnected wires. Maybe we can figure out how to move or how to rotate the 1-3 grid if we consider the letters PASS all appear on the same row.

To help visualizing the various kinds of characters in the main grid:
Edit (@gcampbell): reminiscent of Befunge. :) Also, in Befunge, @ is the end-of-program character.

2-2

This contains a gif. After a while we're greeted to this.

We can see the 6 colours, bcgmry, and what looks like a portal reference. I believe this hint ties up with 2-1. I don't think the words "Security" and "This is ..." are of importance.

2-3

A sign with the message "The League of Puzzlers. Only the worthy may enter."

I believe this is a subtle hint for something. Maybe a meta reference from this site?

3-1

More brick walls. This is also likely to be nothing, though I'm not entirely convinced...

3-2

Image of the door. Someone tried to (brute?) force their way in without success. Could this mean anything? I'm leaning towards no. Could perhaps mean that no brute force solutions are possible (which might help eliminate methods that won't work).

3-3

A (green) message with the words "Nothing@All". This is probably a hint for the meaning of the character @. One suggestion: "@ is where All begins" so it could be some sort of starting point. Another interpretation could be it us irrelevant and it is literally nothing at all. While @ appears in 1-3, it doesn't seem to be integral to the puzzle and we don't have the letter L to spell out the word in 2-1.

4-1

Contains the missing parts of 1-1 and 2-1. That's all, it seems.

Update: Note that the pieces of paper were recently discarded in the bag. This means that the "install" grid may have been updated recently, whereas the schematics on the business card may be older. As a consequence, the schematics may not be up to date, may not be layed over the grid, but could be indications on the kind of puzzle.

4-2

Cracks on the ground. The phrase "looking for your dignity" feels like a hint this is meaningless, but it's far from certain. All of the pointless images seem to be contained in the second column of the mega-image.
Could imply that the answer has to do with the grid lines between the characters? Note that the 11x11 grid can be demarcated by 10+10 lines, which intersect at 100 points; and a number from 0000-9999 could describe all 10000 combinations of a pair of these points.

4-3

Hints for our convenience (nicely executed, too). Most of them seem directly relevant to the keycode & passcode image, so it's likely everything else is a challenge to decode it and extract the passcode (solution).

- 10000, 5040, 715, and 210: (credits to f") the number of ways to select 4 digits in order, 4 distinct digits in order, 4 digits without order, and 4 distinct digits without order. Could this mean we're looking for 4 distinct numbers? Or simply that the previous puzzler calculated how many attempts would be necessary?
- X and %: A hint that we're supposed to substitute % for X in 2-1.
- Which way up?: This could refer to any grid in the puzzle, i.e., 1-1, 1-3 or 2-1. Update: the drawn grid looks like a number sign (#); it could be a clue on how to interpret this sign in the 2-1 grid.
- 0000 = ENTERPASSCODE?: Hint of the input/output relationship in 2-1.
- Upper/lower: This probably hints the lower and upper case letters refer to different things in 2-1. See there for further deductions.
- Am I not worthy?: A gentle reminder that 2-3 is not unimportant.
- Crossed out notes: They most likely refer to the letter grid in 2-1 and hint at likely guesses we'd arrive at which are incorrect. The bottom line reads "The blank spaces must mean something", which is what motivated me to remove them in 2-1.

• If we think of the grid as a 2D programming language like f'' said, @ may be a no-op from the "Nothing@All" image. There's also the # with the four arrows going out of it, which I haven't made sense of yet. % as an X could denote program termination. Apr 28 '16 at 8:36
• 10000, 5040, 715, and 210 are the number of ways to select 4 digits in order, 4 distinct digits in order, 4 digits without order, and 4 distinct digits without order.
– f''
Apr 28 '16 at 8:45
• I think the logo on the business card shows how the grid is supposed to be used. Maybe # gives out lines in all four directions, while % blocks them. < and > could make the lines bend.
– f''
Apr 28 '16 at 8:48
• @f'' The logo's dimensions are 7 x 11 (rows). I tried overlaying it on top of the grid, but every possible position it fit in had the line pass through a %. Apr 28 '16 at 8:55
• @all FYI: without making any comments on the correctness (or otherwise) of any of the above information, I've fixed a typo and included the full, formatted grid as text, because I don't want people wasting their time due to a minor transcription error. Apr 29 '16 at 3:16

You paste the sticker back onto the keypad:

And reassemble the scrap of paper:

• In the two-digit numbers, the squares with those digits are always separated by one square with a question mark. Digits in adjacent numbers are diagonally adjacent.
– f''
Apr 28 '16 at 5:57
• Presumably we need to find the code that will produce the phrase "ENIGMATIC"?
– f''
Apr 28 '16 at 6:52
• In the second image, "<" and ">" seem to represent left and right turns. Ex. to go from 3-2 to 4-9, you have to turn left.
– f''
Apr 28 '16 at 6:55
• There are two each of the lowercase letters bcgmry. These are the initials of six colors (blue, cyan, green, magenta, red, yellow).
– f''
Apr 28 '16 at 7:12
• Looks like they're portals, from the drawing under the color wheel.
– f''
Apr 28 '16 at 7:18

EDIT: After reading Alconja's hint, I think that much of what I first posted may be over-thinking it. Also, we need to find out which 3 images are the key ones. My guesses:

1. The security panel almost certainly, especially given Alconja's comment about how NOGUESSING->DONTGUESS changes things.

>

2. By corollary, the trash bag is probably essential too, as it lets us reconstruct 2-1.

>

3. If I guessed correctly in 1 and 2, the 3rd is probably the business card, as it tells us to look for the numbers that give ENIGMATIC.

>

The old puzzler's notes are probably helpful hints about what to not try. I'm leaning toward the number grid with question marks on it as being a red herring, as it seems to have nothing to do with the security panel.

I looked at the actual enigma machine on Wikipedia, and there seem to be several similarities to this puzzle:

1. The enigma was an electro-mechanical machine: we see green wires coming from the keypad into the system setup, and then out to the output. This would seem to support the 2D programming language hypothesis.

2. If this is enigma-like, remember that the enigma had a wheel that rotated every time a letter was entered. Possibly the color wheel is a rotating cipher wheel that increments every time a number is entered.

3. Every number input has to make multiple letter outputs: ENTERPASSCODE is 13 letters, which we got from 4 letters. This supports the rotating color wheel hypothesis: with a very small change in input, we see a very large change in output (again a characteristic of enigma machines).

4. Which way up? may refer to which way we overlay the wiring diagram on the business card onto the system setup image. I tried it with the business card right way up: the scalings for both directions were not equal, and some lines fell on the squares, while others fell in-between.

5. After Alconja changes NOGUESSING to DONTGUESS, note that ENTERPASSCODE, DONTGUESS, and ENIGMATIC can all be made by a single pass through the string in 2-1. Maybe it's a modified two-tape Turing machine: the head moves along the string according to specific instructions, and reads out the capitals it lands on.

• Oh man, this is embarrassing. You just alerted me to a second typo... 0001 actually produces DONTGUESS ... Again not at a computer right now, but will update the images ASAP... Apr 29 '16 at 22:22
• @Alconja That sure changes things.
– dpdt
Apr 29 '16 at 22:49
• I know, hence the embarrassment. The password/passcode one was just a typo, this one actually matters... Apr 29 '16 at 22:57
• @Alconja What a clever way of giving a hint of what is important ;c) Joke asside, I know how it feels to make a perfect puzzle and then discover a mistake. Don't worry, most here understand. As long as you fix it and keep creating lovely content, you're always forgiven :c) Apr 30 '16 at 17:21

The letters r, g, b, c, y, m could provide the directions NE, NW, S, SW, N, SE according to the gif 2.2 and thus form a complete compass together with the arrows >, < (E, W).

Using the idea of < and > being left and right directional arrows when following the rows and columns of the number grid found in number grid I came up with the following grid which may be of use. This might combine with the North, East, South, West NESW approach for a solution. (Also I included greyed out @ signs for where there were gaps after following the arrows - to match the idea that @ means "Nothing@all")

• Can you explain a bit how you came up with this? Am I missing anything, or is this board inconsistent with 12 > 5 > 76 and 87 < 9? Apr 29 '16 at 11:53
• @Reti43: Each number denotes either a row or column that contains its digits. Adjacent numbers denote one row and one column, and the cell at their intersection contains the sign. No idea beyond that. Apr 29 '16 at 12:55