# Questions tagged [cryptography]

A puzzle concerning techniques for secure communication in the presence of (hostile) third parties. Do NOT use this for simple "crack the code" problems; use [cipher] instead.

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### Two Sheriffs and Eavesdroppers - 3

“The Two Sheriffs” puzzle was already discussed here. This puzzle has only one difference: we have six suspects instead of eight. Two sheriffs in neighboring towns are on the track of a killer, in a ...
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1 vote
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### Scheme to select a multiple choice answer on a whiteboard secretly? [closed]

Trying to set up a cute demonstration of cryptography, here's what I'm envisioning so far: I have a whiteboard, some number of students, and an equal number of different colored markers. On the ...
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### The dessert problem (blind ballot remaining blind if non-unanimous) [closed]

A group of (possibly over-polite) people have just finished their meal at a restaurant. One of them asks, "Does anyone want dessert?" The table goes quiet. Some of the people might want ...
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### Judgment-free construction of a playlist

Alice and Bob are planning a long car trip and need to come up with a playlist for it. For any given song, they have one of four opinions on it: "That's, like, my favorite song ever" (love), ...
75 views

### intercepting the box [duplicate]

If you need to send a message in a box to a person so that no one can intercept it and get the message, how do you do so if you have a padlock and key and they have a padlock and key
186 views

### Really Secure Awesome Cryptography

Really Secure Awesome Cryptography is a protocol for sending messages based on public-key cryptography. Assume that messages are simple text strings of at most 500 characters. Users choose a private ...
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### Why did she choose O6G?

He gave her 8 choices. 7 lead to death, one lets her continue. O6A O6B I6C U6D I6E I6F O6G O6H Of course, he knew she had no idea. He turned the hour glass and gave her 5 items from his suitcase....
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### 2 Person Same Number Verification

Alice and Beth both receive a random integer from 1 through 10, inclusive. They only know the number that they are given. The two of them want to come up with an algorithm to check that their ...
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### What is a Tetris Word™?

This is in the spirit of the What is a Word/Phrase™ series started by JLee with a special brand of Phrase™ and Word™ puzzles. If a word conforms to a special rule, I call it a Tetris Word™. Use the ...
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### A world with roman numeral alphabet

Tomorrow you will wake up and all the letters will be replaced by roman numbers. That'll be "ok" when you'll learn the replacement's order! Nevertheless, today you have the possibility to make it a ...
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Given Hexagon is super secret system with varying levels of access. Users do not have to remember any password. They just have to answer the questions posed by Hexagon strictly in the allotted time. ...
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### A multi-symptom affliction

"Kindly state your name." The nurse's voice was polite, but qiet. "I'm sorry, I can't hear you, my hearing's bad." Being mostly deaf was quite frustrating for our patient. "...
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### Of course, *I* could solve this easily

Question: What do you think about music? Encoded below is part of one of my favorite songs. Rejoice, as the key to decrypt it is a common pattern. The type of thing you might see everyday. You should ...
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### A Magical Cryptography Puzzle

The following is the first and second sentences of one of my favorite (and fairly popular) fantasy books encoded in a cipher I created a few years ago. I'm quite certain it's breakable, but hints/more ...
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### Trying to crack a code [closed]

I am trying this string set of puzzles. The last puzzle to do, began with 055 055 055 055 ...…040 056 055 055 055 055 which translated to: 77777(77777(877 …… 77(87777(87777 But I cannot work out ...
1 vote
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### Stuck trying to figure out a hidden message

As part of an ongoing "treasure hunt" in an online game that I take part in, there have been several forum posts made in an attempt to hint the participants to finding certain locations. However, ...
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Really rare report! Today, Todd texted this: ♦☼ ↓☼§ ♂♫☼↨ ¶◘♣ ☺♫‼○↨♣↕ ♠☼↕ ◄§♣‼¶♥○☼♫ ‼○↑ ☼♫ ¶◘♣ ♪☺¶◘ ◘☼♪♣↨☼♣↕♂? ○ ♥☺♫'¶ ♠○•§↕♣ ○¶ ☼§¶. Although, having solved it, I decided it's too easy and decided ...
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### Flipping a coin across the internet

Suppose you wish to "flip a coin across the internet". ie. You want to show other people that you've flipped just ONE coin, and show them the result. I'm currently trying to think of the simplest ...
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### Finding a serial killer

Recently, in the United States, there have been multiple murders all over the country. Because of how similar these murders are, it is believed that a single individual is responsible. There have been ...
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1 vote
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### Looking for a place

Seems overwhelming but pretty simple. clue.txt http://junewi.000webhostapp.com/testing/clue.txt tdHCR6ieFHNqUv1zQHE0KRiAfypNTApKi2xlN4CMYK2beP3M1u2mgUvRvDmx0M8heyKebUVEsGcbHrnymUIeviUN/...
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Yesterday I found a note under my chair. The note seemed very mysterious so I thought there must be a hidden meaning inside. It read: OJNU OJNU OJNU V YVGRENYYL FGBYR XRLONFR'F PBQR NAQ CBFGRQ VG ...
433 views

### Hack of the International Stamped Time Server

The International Stamped Time Server (ISTS) broadcasts a time stamp integrity-protected with an RSA-4096 public key $(n,e)$. But mere days after it starts operation, hackers announce they pwned it by ...
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### Conspiracy Theories

An entry in Fortnightly Topic Challenge #35: Restricted Title 1. Title based on this xkcd. I think a friend of mine sent me a letter. However, I can't seem to decrypt his message. I'm worried about ...
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### Determining the meaning of a challenge coin

I saw this rather cool looking challenge coin the other day, and I was wondering what the associated binary on the back of it means, as it isn't standard ASCII. I'd appreciate it if you all have any ...
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### "I like things done once"

You disable the security shields. Dr P releases his minions. Suddenly you hear the red siren. 'Code-Red' says the computer. You smell smoke. You see the background a blur and noises in the air. ...
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### Mathematicians play hide and seek!

The ghosts of Eratosthenes and Euclid are playing hide and seek. They can hide anywhere in all of space and time, but the pair are in agreement to play somewhere on earth within the years 0 to 2000. ...
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Inspired by the famous "how to send a locked box without pre-shared keys" puzzle, I have designed a Truly Clever and Very Secure cryptographic protocol for situations where you must send a secret ...
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### How to Complete this Cryptographic Challenge?

I've been trying to solve this cryptographic challenge for months: ...
481 views

### Two mysterious cave notes

Fellow puzzlers! On my vacation to Norway last summer, I've gone on several hikes through the mountains. While the views were absolutely amazing, the hikes also left my with a mystery... On, if I ...
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### Code Cracking 1984

This is a code from an old home computer magazine. Still it is unknown the cipher used for it, although they gave the solution: ...
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### A half successful police raid

Everything in the next section is flavor text only. You may skip right over it, if you´re impatient. "So, how did it go officer? I hope there was no blunder this time!" The chief commander ...
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### Late 18th/early 19th century numbers grid

I was researching an historical figure on the Isle of Man, Capt George Quayle (b.1751 - d.1835), and in amongst the museum's papers was this numbers grid which was part of his effects. The museum ...
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### Is this a known technique or a custom technique?

I recently watched "A Good American," and I'm wondering what the decryption method is that he is using here, or is it a custom decryption method? He slides an array of letters printed on paper over ...
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### A Puzzle With the Difficulty Level of Dessert

I have built an encoded message here. Read and ponder. In this particular case I have encoded the name of an American known all over. My method is simple. Don't be fooled. Although this is a short one,...
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### What am I trying to say?

This is an enigmatic puzzle. The puzzler must deduce what kind it is and solve it with no help.
543 views

### Meteor strikes again

Part of a phone call: -...well why didn't you just say so? -It wasn't as easy as you thought, Jack. All the power lines here were destro--- -I know...It's not like we're living on a different ...
782 views

### A simple "scientific test..."

I hold every single day, in my lovely picture frame. I look a hundred years old, but I was built on the spot. You might say I'm weak, and I'm four times over the hill. Sometimes I take the elevator ...
665 views

### An endless loop in a desolate wasteland

You check your position tracker. Back at the beginning. Slowly, once again, you begin taking steps and counting cracks in the sidewalk. One. Two. Three. Four. Five You look around. Pitch darkness....
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### BFTIODFTTWKBCSC

This is my first self-developed cryptographic puzzle. I hope it is neither too hard nor too easy for you to break, and that you enjoy it. Please do not only post the answer, but also your way towards ...
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### An alphametic cryptogram with clues

At college you know your roommate is reading books about cryptography. When looking at his journal you see the following entries. You decide to figure out the code and follow him around for a few ...
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### Deus Ex crypto puzzle

There is an encrypted email in the recent Deus Ex: Mankind Divided game: From the game files, this appears to be the string: ...
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### The Answer Exists - Cryptography

I have a nice riddle for you. It involves cryptography. At last, he thought. We're finally out of this town. "New town, new beginnings" said to himself. Row after row, they passed through the ...
213 views

### Treasure hunt 'round the world! (clue 5)

If you're interested in starting the treasure hunt from the very beginning, check out the prologue! After solving the monotonous and mindless puzzle (of course jet fuel can't melt steel beams), you'...
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### For a puzzler such as you, you shall solve with ease

Your pet cricket has disappeared, due to its undying loyalty and steadfastness you assume foul play must be afoot! After looking around for any signs of confrontation, you find none, but thankfully ...
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### A (trigonometric ?) cryptography riddle

Tan: Why did $sin$ eat a sandwich? Cot: Just $cos$! After seeing this small "joke" made by Tan and Cot, Sin replied: "Well, I have something better than jokes: riddles! Can you solve ...
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Saturday, 2nd April 2016 - somewhere several meters below surface "Report, agent." "Mission 'Capture the bird' was not fully successful, sir. The ...
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### Remorseless Riddle Rampages Relentlessly

"Fine day" says I "Need a sardine?" "Why - no thank you" - replied Cecil the 3-Eyed Spleen "How then will you get in Through that nasty great door?" I ask. He said "Slowly - slowly - lather myself ...
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### For Memorial Day

I was asked to bring something specific for our big Memorial Day Barbecue. I was told to bring an item which is depicted by the following six pictures, though I'm guessing I shouldn't take things at ...
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