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Questions tagged [cipher]

For challenges relating in some way to encoding messages using classical (pen and paper) ciphers. For modern ciphers, such as AES, use the [encryption] tag instead.

17
votes
13answers
1k views

Trifid Cipher (without keyword)

Introduction: I have loads of different ciphers stored in a document I once compiled as a kid, I picked a few of the ones I thought were best suitable for challenges (not too trivial, and not too ...
13
votes
11answers
2k views

Computer Cipher

Introduction: I have loads of different ciphers stored in a document I once compiled as a kid, I picked a few of the ones I thought were best suitable for challenges (not too trivial, and not too ...
28
votes
18answers
3k views

The Improved Caesar Pig Latin Cipher

The problem with the Caesar cipher is the resulting words are often unpronounceable. The problem with Pig Latin is that it is easy to decode. Why not combine them? Input A word consisting of the ...
15
votes
14answers
1k views

A Capital Cipher

Your task is to decipher a non-empty string consisting of printable ASCII characters in the range [32..126]. Reading the string character per character: each time you encounter a letter in lowercase,...
20
votes
15answers
3k views

The Keyboard Shift Cipher

Given the following input: An integer n where n > 0. A string s where ...
0
votes
5answers
171 views

Encrypt a string using vigenere techniques [duplicate]

Your task: Create a program that encrypts a string with another string using a key, using the vigenere cipher. What a vigenere cipher does ...
38
votes
13answers
5k views

579085261 is CRAZY, 725582 is GOLF, 10757494 is …?

Your task is to translate a 103-smooth number into an English word, using the method described below. How? Generate the list of prime factors (with repetition) of the input number. Sort the list: ...
19
votes
9answers
1k views

Garbled Phone Numbers

You know how you get a voicemail message and the person's connection wasn't great, and you're trying to figure out how to call them back, but you're not sure if that was a "5" or an "8" they said? ...
19
votes
16answers
1k views

Incremental Cipher

This task is rather simple, and makes use of three distinct "operator" characters. Your task is, given a simple sequence of letters, perform the following task to encode it using ...
35
votes
17answers
2k views

Let's do some “enciph5r47g”

This is the inverse of Let's do some "deciph4r4ng" In this challenge, your task is to encipher a string. Luckily, the algorithm is pretty simple: reading from left to right, each ...
57
votes
36answers
4k views

Let's do some “deciph4r4ng”

In this challenge, your task is to decipher a string. Luckily, the algorithm is pretty simple: reading from left to right, each encountered digit N (0 to 9) must be replaced with the character which ...
-1
votes
1answer
248 views

Encode the backwards alphabet cipher

Given a string of text that contains lowercase letters, encode it as follows: (I will be using abcdef) First, encode the alphabet cipher, but this time, 0-indexed. ...
1
vote
0answers
95 views

Encode the simple substitution cipher [duplicate]

Review First, let's review the Simple Substitution Cipher. To encode a string in the Simple Substitution Cipher, replace each letter in your string with another letter. A letter may not be used to ...
26
votes
16answers
2k views

Decode Baby-talk!

When babies open their mouths, they're not just spewing gibberish. They're actually talking in a highly advanced, adult-proof cipher... The Baby-talk Cipher When a baby talks, it could look ...
9
votes
25answers
595 views

Encode the column cipher

Given a string to encode, and a number of columns (the key), encode the string as follows: I will be using the example Hello, world! and the key ...
19
votes
35answers
2k views

Encode the alphabet cipher

Given a string that contains lowercase letters, encode that string with the alphabet cipher. To encode with the alphabet cipher (I will be using the example hello):...
13
votes
10answers
770 views

ASCII Odd/Even Cipher

We'll define the ASCII Odd/Even Cipher via the below pseudocode: ...
11
votes
2answers
230 views

Marcel Proust and Markov decipher security service’s T9 texts

As if this challenge could be any more Pythonesque in spirit... No prior knowledge of Markov chains or encryption techniques is required. You are a spy who needs to obtain some crucial information ...
7
votes
10answers
626 views

Columnar Transposition Cipher

Columnar Transposition Cipher While I have plenty of programs I have written for more advanced ciphers, I just realised I don't actually have one for one of the simplest: Columnar Transposition. The ...
6
votes
2answers
500 views

ADFGX Cipher Encryption

ADFGX cipher encryption The ADFGX cipher was used by the German army in WWI. Write a program to encipher with it! It works as follows: Create a 5x5 Polybius square with a mixed alphabet. The ...
21
votes
15answers
2k views

Caesar Shifting

A Caesar shift is probably something we're all familiar with. (You might be even doing it as a homework task. If so, please don't copy these answers, your teacher almost certainly doesn't want ...
8
votes
6answers
4k views

Rail fence cipher

Write two programs: - One which reads a string and a key and encodes the string into a rail-fence cipher using that key. - Similarly, write a program for the reverse function: deciphering a rail fence ...
27
votes
17answers
4k views

Decipher a Vigenère ciphertext

The Vigenère cipher was a simple polyalphabetic cipher that basically applied one of several Caesar ciphers, according to a key. Bascially the letters in the key indicate which shifted alphabet to use....