Questions tagged [cipher]

A cipher is a simple method of modifying messages to make them unreadable except to readers who know the key. Common ciphers are Caesar, Vigenere, Atbash, and several types of substitution cipher. Other ciphers include polygraphic ciphers such as Playfair and Foursquare and numerical ciphers such as Polybius and Nihilist. Cipher puzzles sometimes make use of data encodings like Morse, Binary, or Base64.

What is a cipher?

A cipher is an encoded message, usually by substituting letters for other letters, numbers, or symbols.

What makes a good cipher puzzle?

A cipher puzzle has to be solvable. There should be an intuitive and enjoyable solution path, and preferably one or more 'aha' moments. In case of multilayer ciphers, it's a good idea to provide the solver some confirmation after each step. See Code Puzzles: What (Not) To Do? for more on this.

How should I try to solve a cipher puzzle?

Try to see what kind of cipher it is - whether you need to use rot13, or Morse code, or unscramble something. Then, if it has more than one layer of encoding, you can continue with the same for the next level.

How should I answer the question once I have the solution to the cipher?

  • Make sure your solution fully fits the original message.

  • Answer the cipher fully, and provide a detailed explanation. Provide a line-by-line analysis if necessary to justify your solution.

  • Spoilertag content that directly relates to the answer, but do not write an answer entirely in a spoiler. Spoilertags hide part of a post by placing >! at the beginning of a line.

A Guide

See this Guide to Codes and Ciphers for more info.

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What characteristics of a ciphertext can be indicators of a particular cipher?

If I have a ciphertext, what information about the probable ciphers used can I infer from the ciphertext itself? For example, information from: the length the spacing / grouping of characters the range of characters used frequency counts and any…
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Secret Admirer Secret Message

There are 4 interns at the new government agency. All 4 are comp sci majors. John is the only male. The three girls are all close but secretly like John. Lisa is playing hard to get and hopes John will make a move but could trick John into asking…
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Break the subsitution cipher with a twist

Breaking news: the NSA can break letter substitution ciphers. (Letter frequency, guessing the word "the", et cetera...) So, let's make our secret code more secure. Let's apply the secret substitution n times to the nth letter of the message. Here's…
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Resistance is futile

On the sunny morning of April 5th, 2063, an alien spaceship started orbiting the Earth. Among the cries of "It's an alien spaceship!" and "Ohm my god!" from the people, governments noticed that they were beaming down a colorful…
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A cipher for beginners

I have been lurking on puzzling.se for quite a while, but I never joined the community before because by the time I figured out any puzzles, someone else had already answered them. For that reason, I decided to put up this puzzle. It is pretty…
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A mysterious email from Ryanair

You are a secret agent in the service of the KGB, and after a setback when the higher-ups thought your cover had been blown, you have embarked on a highly dangerous mission to infiltrate MI6. Under the pseudonym of Flynn Smith, you are working…
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Solving an encoded message at the bottom of a Bletchley Park mug

A while ago (maybe even a few years ago) I was given a Bletchley Park mug that is black when cold. When it heats up (from having a hot drink inside it) it turns white and reveals a sequence of pictures and a message about Bletchley Park at the…
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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 it. You are Alan Turing 2.0 - a British…
Alexander
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Invade the Pyramid if you Dare

Before you lies a pyramid, with a giant statue blocking the entrance. ab abcd I D abcdHf abOdefgh abcdSfghij N abcdefghijkl …
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The strange SMS

I was talking with a friend via SMS when suddently, he sent me a strange message : (16)(39)(26)(36)(25)(34)(12)(34)(47)(36)(28)(18)(36)(33)(22)(12)(18)(18)(23)(37)(39) I asked what was going on but he didn't answer me ... Can someone help me, what…
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Safe combination for your heritage

Phillip, a 68 years old man, was near the end of his life. Before passing away, he decided to hand to his daughter a piece of paper with the following: 48 7A 2D 38 8B On the back, there was the following text: DEATH, what unpleasant surprise. While…
Ismael Miguel
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Known Algorithm Attack: Caesar Reloaded

Most of the puzzles here revolve around an unknown algorithm attack. That is, you are given an enciphered piece of text and asked to decode it (and often given a series of hints which describe how the enciphering was done), or you are given a set of…
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Dot message on a Star Wars frisbee team

So I was given this image to "decrypt"/ figure out the message and report back. However I am completely lost... Can anyone give me an idea of where to start? Can anyone solve this? Thanks for whatever information you can give me! Note: Star Wars…
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The Hunting of the Snark: Given ciphertext and plaintext, what cipher is used?

This is a cryptogram puzzle. Below is some text; each section of the original text ('plaintext') is followed by an encoded version of that text (the 'ciphertext'). Your challenge is to explain the encoding for each section. Most of the ciphers are…
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The Twenty Doors! (ROOM 1)

This is part of The Twenty Doors series. The next one is The Twenty Doors! (ROOM 2) You stand in a small, dark room. You have no idea where you are. Then, you see a message in front of you. Welcome to the dungeon! In each room, there is some…
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