Questions tagged [cryptography]
For challenges involving cryptography, including things like ciphers and hashing algorithms
63 questions
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Shortest possible valid PEM-encoded CA certificate
The challenge is to create the shortest possible PEM-encoded CA certificate. The PEM format is specified in rfc7468 (section 5.1 shows an example certificate), and the structure of certificate data (X....
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Produce a secure block cipher round function (1 bit round key; 7 bit message) [closed]
We need to produce a block cipher round function with a 1 bit round key size and a 7 bit message size with the highest level of cryptographic security according to our measure of security.
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Encrypt AES256 (ECB Cipher Mode)
I've looked and could not find a post for this, if there is one, I'll remove it quick! Related and also related
The goal is (hopefully) clear: create the shortest code (in bytes) that implements the ...
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MD5 Hello, World!
MD5 checksums are relatively easy to crack. For this challenge you will create two separate programs, the first one writing Hello, World! and the second one writing ...
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just a caesar cipher... with a twist [closed]
I have been going to puzzling.se, and people over there write stuff in rot13 a lot, sot this gave me an idea:
Write a program that takes 2 inputs, a string and integer:
the message to encode or ...
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Russian Caesar cipher
The objective
Given a Russian text, encrypt it with Caesar cipher with key 16.
The basic Cyrillic alphabets
The basic Cyrillic alphabets are: (U+0410 – U+042F)
...
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108
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Proving that a Russian cryptographic standard is too structured
The aim of this challenge is to find an impossibly short
implementation of the following function p, in the langage of your
choosing. Here is C code implementing it ...
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11
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Convert alphanumeric (base-36) sentences into hexadecimal (base-16) sentences
I use "sentence" here loosely to mean "any sequence of words separated by spaces" and "words" to mean "sequences of alphanumeric (hexatrigesimal) characters unseparated by spaces".
Conversion is from ...
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Generate an RSA key pair
Given a positive integer \$N >= 4\$, output an RSA key pair (both the private and the public key) whose key length is \$N\$ bits.
The RSA key generation algorithm is as follows:
Choose an \$N\$-...
user45941
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Gimli, make it even shorter?
I'm one of the authors of Gimli. We already have a 2-tweet (280 chars) version in C but I would like to see how small it can get.
Gimli (paper,website) is a high speed with high security level ...
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Shifting Caesars Shifts
Description
A Caesar Shift is a very simple monoalphabetic cipher where each letter gets replaced by the one after it in the alphabet. Example:
...
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Straddling Checkerboard Cipher
The Straddling Checkerboard is a method for converting letters to numbers and was part of a pencil an paper cipher known as VIC
To convert letters to numbers first you have to make a checkboard like ...
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Decode the hidden message!
Introduction
One day, you were just relaxing in your office in the CIA, when suddenly you see an alert on your computer. Your programs have just intercepted hundreds of coded messages! A quick ...
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Shh... Can You Split a Secret?
In Applied Cryptography by Bruce Schneier (which I have been reading quite a lot recently), a protocol for splitting secrets is discussed. Here is a brief description:
Trent generates a random ...
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Generate a cipher
Generate a cipher given a number and string
Your task is simple. Given a string s and a number 0 <= n <= 9 as inputs, ...
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Out Steganograph Me! [duplicate]
Out Steganograph Me
As a follow up to this challange, I want to see competitive algorithms for encoding strings as images, and then decoding them.
The Challenge
Your goal is to write a function or ...
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Decipher Neurotic Frogs
Decipher Neurotic Frogs
Now that Puzzling.SE has finally cracked my amphibian-obsessed cipher, let's write a program or function to decrypt it!
(If you want to look at the puzzle before having it ...
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PKCS#7 padding validation
In cryptography, PKCS#7 padding is a padding scheme which adds a number of bytes N ≥ 1, where the value of each added byte is equal to N.
For example, Hello, World!...
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Write a VIC cipher decoder
You've received a coded message from your ally that you know is encoded with the VIC cipher. As you know that the VIC cipher is notoriously convoluted, you want to write a program that will decode the ...
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Write a VIC cipher encoder
The VIC cipher is one of the most complicated pencil and paper ciphers ever devised. Used in the 1950s by Soviet spy Reino Häyhänen, codenamed "VICTOR", its main principle is security through ...
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Print a Tabula Recta!
The Tabula Recta (sometimes called a 'Vigenere Table'), was created by Johannes Trithemius, and has been used in several ciphers, including all variants of Bellaso's Vigenere cipher and the Trithemius ...
user53406
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Help the poor Cryptographers - DLP Edition
Introduction and Motivation
I'm mainly active on Cryptography.SE and as such have already stumbled across the question: "How the hell am I supposed tools like cado-nfs to do stuff!?". They ...
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Shamir's Secret Sharing
Given n (the number of players), t (the threshold value), and s (the secret), output the <...
user45941
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Time for some TEA!
Introduction
A while back I stumbled across the tiny encryption algorithm (TEA) and since then I have recommended it whenever special cryptographic security properties were un-needed and a self-...
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Substitution cipher [duplicate]
A substitution cipher is an encoding method where each letter in the alphabet is replaced with a fixed, different one; for example, given the following substitution map:
...
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Crack the Cipher [duplicate]
Write a program or function that will break ciphers, using as few bytes as possible.
Task
Given an encrypted message and a dictionary as input, output the decrypted message. The messages will be ...
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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 ...
user50171
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Atbash Self Palindromes
Consider the Atbash transformation:
A|B|C|D|E|F|G|H|I|J|K|L|M
Z|Y|X|W|V|U|T|S|R|Q|P|O|N
Where A ⇔ Z and L ⇔ O, e.g. There is an interesting property that ...
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Bacon's cipher: An Intro to Steganography
This little piggy went to market, this little piggy wrote some code...
Ah wait, we're not talking about that bacon, we're talking about Sir Francis Bacon! Specifically, the cipher Bacon devised in ...
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Convert ciphered Roman numerals to Arabic decimals
Write an algorithm to interpret a sequence of letters as a Roman numeral. (see roman numeral rules below)
Each distinct letter has a matching Arabic decimal value, no maximum. But you don't have ...
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An Affinity for Ciphers
Description
You, an armchair cryptanalyst, have noticed that the first letters of each word in your neighbor's mail (yes, you read it -- how else would you know if he's plotting something?) look very ...
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The Drunken Bishop
In public-key cryptography, a public key fingerprint is a short sequence of bytes used to identify a longer public key.
In SSH in particular they can be used to verify that a server is in fact the ...
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Crack a Vigenère Cipher
A Vigenère Cipher is encrypted by repeating a keyword to be the length of the plaintext, and summing each character in that text with the corresponding letter in the plaintext modulo 26. (using A=0,B=...
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Cryptic Kicker //
Cryptic Kicker
A common but insecure method of encrypting text is to permute the letters of the alphabet. In other words, each letter of the alphabet is consistently replaced in the text by some ...
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A fiercer four-square cipher
Background
One-hundred and thirteen years ago, amateur cryptographer Félix Delastelle published his work on the four-square cipher, a digraphic substitution cipher that accepts two permutations of a ...
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CipherSaber encryption
Implement a CipherSaber encryption program, as described below. Guidelines:
The smallest entry, in bytes, wins.
However, in a departure from code-golf norms, you are welcome to post interesting ...
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Cryptographic hash golf (robbers)
This contest is over.
There are no remaining crackable answer in the cops challenge.
Companion thread of Cryptographic hash golf
As a reminder, here are the rules for robbers from the main ...
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Cryptographic hash golf
This contest is over.
Due to the nature of cops-and-robbers challenges, the cops challenge becomes a lot easier when the interest in the associated robbers challenge has diminished. Therefore, ...
- 212k
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Shifty XORyption
Write a program or function (or set of programs/functions) to encrypt and decrypt data given the following specification:
Encryption
Calculate an XOR hash of the input by XOR-ing every byte with each-...
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Decrypting a block of AES
Today your goal is to decrypt a secret message using AES. Given a ciphertext and key you will decrypt and print the message.
Your program may be in any language. It will be run with input on stdin, ...
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Solve a Date Shift Cipher [duplicate]
Introduction
In this challenge you will be solving date shift ciphers. Here is a general overview of what a date shift cipher is. To encode a message, you first must make a key. A key in a date shift ...
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Solve a Diagonal Burrows-Wheeler transform
Introduction
In this challenge you will be solving diagonal Burrows-Wheeler transforms. Here is a general overview of what a diagonal Burrows-Wheeler transform is. To encode a message, you first must ...
- 7,642
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Key length of Vigenère cipher
The Vigenère cipher is a substitution cipher where the encryption of each letter of the plaintext depends on a different character in a keyword. This stops you using simple methods of frequency ...
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Compress and Decompress sentence using vowel based encryption cipher [closed]
The aim is to parse a sentence and compress/encrypt it according to the rules below and then decrypt it using the ...
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2nd byte bias of RC4
Short version
RC4, designed in 1987, is one of the most famous stream ciphers. This question asks you to practically demonstrate its 2nd byte bias (for a ...
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What ROT is this? - decrypt ROT-n
Here are the letters of the English alphabet in order by frequency:
e t a o i n s h r d l c u m w f g y p b v k j x q z
That is, ...
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Write a Playfair encryption program
Write a program that takes two lines of input and uses the first as a key phrase to encrypt the second according to the Playfair encryption technique.
Wikipedia describes Playfair encryption in some ...
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Implement ROT-47... in ROT-47
Challenge: Implement ROT-47 in code that works as both itself and as the ROT-47 version of itself.
Scoring:
Your score is calculated as a percentage of used, ROT-47 eligible bytes in total of both ...
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Build an RSA encoder
Your task is to build a function in any language that takes a message m, an encryption e, and a modulus ...
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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 ...
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