Level I Challenges

92 published challenges (in level I), sorted by:
The Syllabary Cipher – Part 1
Description
The Syllabary cipher seems to be just another substitution cipher, but is it? Find out and solve its mystery!
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125 users have already solved this challenge, 23 are working on it.
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Merkle-Hellman Knapsack Challenge - Part 1
Description
The legendary Merkle-Hellman Knapsack cryptosystem is not suitable for hiking, but it is considered a pioneer of asymmetric cryptography. Can you crack the ciphertext?
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48 users have already solved this challenge, 7 are working on it.
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Alberti Challenge — Part 1
Description
This challenge is about one of the oldest polyalphabetic ciphers. Can you crack this centuries-old puzzle?
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121 users have already solved this challenge, 14 are working on it.
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Wheatstone Cryptograph — Part 1
Description
The Wheatstone Cryptograph is a simple device that resembles a clock with two hands. For each hand there is a ring of symbols. Are you able to decrypt the given ciphertext?
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98 users have already solved this challenge, 8 are working on it.
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Find the right route — Part 3
Description
This series deals with a grid — a basic tool cryptographers use to separate sequences of data into columns and rows. In this challenge you are given three grids where the first grid gives you hints to reveal the plaintext of the second grid. Are you able to find the right route?
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29 users have already solved this challenge, 5 are working on it.
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Find the right route — Part 2
Description
This series deals with a grid — a basic tool cryptographers use to separate sequences of data into columns and rows. In this challenge you are given four grids where the first grid gives you hints to reveal the plaintext of the second grid. Are you able to find the right route?
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31 users have already solved this challenge, 2 are working on it.
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Find the right route — Part 1
Description
This series deals with a grid — a basic tool cryptographers use to separate sequences of data into columns and rows. In this challenge you are given two grids where the first grid gives you hints to reveal the plaintext of the second grid. Are you able to find the right route?
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85 users have already solved this challenge, 16 are working on it.
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Lightweight Introduction to Lattices — Part 2
Description
Lattice-based cryptography schemes are relevant for current post-quantum cryptography research. This challenge series accompanies the basic theory from a chapter of the CrypTool Book called "LIGHTWEIGHT INTRODUCTION TO LATTICES". This part of the challenge series uses vectors to hide a famous quote in modern art. Can you reveal it?
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40 users have already solved this challenge, 4 are working on it.
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Lightweight Introduction to Lattices — Part 1
Description
Lattice-based cryptography schemes are relevant for current post-quantum cryptography research. This challenge series accompanies the basic theory from a chapter of the CrypTool Book called "LIGHTWEIGHT INTRODUCTION TO LATTICES". In this part of the challenge series we introduce systems of linear equations to find a hidden message in a picture.
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56 users have already solved this challenge, 5 are working on it.
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Polyhomophonic Substitution — Part 1
Description
This part of the challenge series is a warm-up with homophonic substitution. In a homophonic substitution cipher, there are more than one ciphertext symbol for each plaintext symbol. The key is a mapping.
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53 users have already solved this challenge, 6 are working on it.
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Cryptanalysis Hacking Puzzles — Part 2
Description
Solving this challenge is not as hard as finding the needle in a haystack, isn't it?
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196 users have already solved this challenge, 37 are working on it.
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Cryptanalysis Hacking Puzzles — Part 1
Description
Three messages were delivered — two encrypted, one in clear. Can you solve the puzzle?
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32 users have already solved this challenge, 34 are working on it.
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Autokey Cipher
Description
The autokey cipher uses only a short keyword and the plaintext to encrypt messages. Are you able to break the given ciphertext?
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173 users have already solved this challenge, 11 are working on it.
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Modular Sequences
Description
What do you know about modular sequences? Work it out.
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77 users have already solved this challenge, 35 are working on it.
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Number Sequence — Part 10
Description
How many experience points does Thomas need to reach the 200th level of his new computer game?
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116 users have already solved this challenge, 19 are working on it.
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Advent-Challenge — Part 1
Description
Little Anna has forgotten how to decrypt her ciphertext. Can you come up to her pre-Christmas wish?
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476 users have already solved this challenge, 22 are working on it.
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Number Sequence — Part 9
Description
Are you able to crack the password of Radomil and find the missing 5 digits?
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118 users have already solved this challenge, 66 are working on it.
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New Year's Greetings — Part 4
Description
This series consists of five parts which are based on each other and that will be getting more and more complicated with each part. This part is the actual challenge and tells you the New Year's greeting of the author.
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44 users have already solved this challenge, 12 are working on it.
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New Year's Greetings — Part 3
Description
This series consists of five parts which are based on each other and that will be getting more and more complicated with each part. Part 4 contains a little New Year's greeting of the author and part 5 teaches us something about the weaknesses of this method. Part 3 adds another modification.
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47 users have already solved this challenge, 3 are working on it.
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New Year's Greetings — Part 2
Description
This series consists of five parts which are based on each other and that will be getting more and more complicated with each part. Part 4 contains a little New Year's greeting of the author and part 5 teaches us something about the weaknesses of this method. Part 2 modifies the encryption of part 1 a little bit.
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49 users have already solved this challenge, 2 are working on it.
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New Year's Greetings — Part 1
Description
This series consists of five parts which are based on each other and that will be getting more and more complicated with each part. Part 4 contains a little New Year's greeting of the author and part 5 teaches us something about the weaknesses of this method. Part 1 is the easiest part of this series.
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53 users have already solved this challenge, 18 are working on it.
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Image Noise
Description
Both images in this challenge seem to contain no information at all. Or do they trick us? Find the secret message.
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154 users have already solved this challenge, 24 are working on it.
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News from Castle Mansfeld
Description
The story of the simple bookseller Paul from Eisleben and his beloved from the near Castle Mansfeld will be continued: A second postcard has been found. Can you decipher the encrypted message?
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58 users have already solved this challenge, 2 are working on it.
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Weakened Granit — Part 1
Description
The challenges for the simplified GRANIT cipher, a method that can be done manually, serve as an exercise and use an intentionally simplified version of GRANIT. Part 1 is a ciphertext-only challenge for which both permutation keys are known.
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49 users have already solved this challenge, 5 are working on it.
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Number Sequence — Part 8
Description
How are the numbers interconnected? Can you find the three missing numbers?
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397 users have already solved this challenge, 30 are working on it.
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A hidden word — Part 2
Description
A friend of yours has given you the following text which contains only X and Y characters. He claims that this text contains a codeword. Can you find it?
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112 users have already solved this challenge, 49 are working on it.
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Number Sequence — Part 7
Description
How are the numbers linked? Can you find the two missing numbers?
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92 users have already solved this challenge, 36 are working on it.
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Number Sequence — Part 6
Description
How are the numbers linked? Can you find the two missing numbers?
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161 users have already solved this challenge, 19 are working on it.
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M-138 — Part 1
Description
This is the beginner's challenge in a series about M-138, a manual cipher of the US army which has been relatively save at the beginning of world war 2nd. Part 1 of the series is a ciphertext-only challenge whose key is largely known.
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219 users have already solved this challenge, 14 are working on it.
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The Last Note
Description
You can find a short encrypted note at the end of the novel "Die achte Offenbarung" by Karl Olsberg. Decrypt the secret message!
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99 users have already solved this challenge, 21 are working on it.
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Heartbleed — Part 2
Description
This challenge is based on the Heartbleed bug in OpenSSL discovered in April 2014. Attack a server which is specifically prepared to be vulnerable to the Heartbleed bug. Please note that it is necessary to solve Part 1 first. !!! We had to take off this challenge, as our firewall doesn't allow flawed servers any more -- even if this flaw was offered by will for training and within a sandbox. !!!
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60 users have already solved this challenge, 12 are working on it.
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The solution for this challenge was made public on May 17, 2022, 6:32 p.m., and thus it is no longer possible to get points for this challenge. However, you can still solve it and enter a solution for this challenge.
Heartbleed — Part 1
Description
This challenge is based on the Heartbleed Bug in OpenSSL discovered in April 2014. Attack a server provided by the group for Privacy and Compliance with the Research Institute Cyber Defence (CODE) at Bundeswehr University Munich, which is specifically prepared to be vulnerable to the Heartbleed bug. !!! We had to take off this challenge, as our firewall doesn't allow flawed servers any more -- even if this flaw was offered by will for training and within a sandbox. !!!
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90 users have already solved this challenge, 21 are working on it.
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The solution for this challenge was made public on May 17, 2022, 6:32 p.m., and thus it is no longer possible to get points for this challenge. However, you can still solve it and enter a solution for this challenge.
Enigma Messages with Repeated Letters — Part 5
Description
In this part of this series of Enigma challenges, a plaintext message consisting of three letters which are repeated several times has been encrypted by the Enigma I. What are the first three letters of the plaintext? Show details…Hide details…
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80 users have already solved this challenge, 9 are working on it.
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Enigma Messages with Repeated Letters — Part 4
Description
In this part of this series of Enigma challenges, a plaintext message consisting of three letters which are repeated several times has been encrypted by the Enigma I. What was the setting of the Enigma rotors?
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76 users have already solved this challenge, 4 are working on it.
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Enigma Messages with Repeated Letters — Part 3
Description
In this part of this series of Enigma challenges, a plaintext message consisting of two letters which are repeated several times has been encrypted by the Enigma I. What was the setting of the Enigma rotors?
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85 users have already solved this challenge, 3 are working on it.
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Enigma Messages with Repeated Letters — Part 2
Description
In this part of this series of Enigma challenges, a plaintext message consisting of one letter which is repeated several times has been encrypted by the Enigma I. What was the setting of the Enigma rotors?
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85 users have already solved this challenge, 17 are working on it.
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Trifid Cipher
Description
Two scatterbrained professors exchange messages that have been encrypted with the Trifid cipher. Unfortunately, one of them lost the second of three layers. Will he nevertheless be able to decrypt the message he received from his colleague?
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126 users have already solved this challenge, 6 are working on it.
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Enigma Messages with Repeated Letters — Part 1
Description
In this part of this series of Enigma challenges, a plaintext message consisting of one letter which is repeated several times has been encrypted by the Enigma I. What is the letter we are looking for?
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178 users have already solved this challenge, 32 are working on it.
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Hill Cipher with Sudoku Key
Description
You find a note with strange characters and an unsolved Sudoku on your brother's desk. You are curious and would like to find out what your brother is working on. Can you decrypt the note using the Sudoku?
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106 users have already solved this challenge, 5 are working on it.
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From Russia with Love
Description
Sarah and Igor are exchange students. Sarah lives in Moscow while Igor is in Berlin. To keep their little secrets confidential, they encrypt their emails. Decrypt the message to find out what Sarah wrote this time.
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287 users have already solved this challenge, 32 are working on it.
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Nils away on travel
Description
Nils would like to go on a journey and has given you a note with information about his destination. The note is encrypted. Can you find out where he would like to go?
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174 users have already solved this challenge, 14 are working on it.
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Snow White and the seven dwarfs
Description
The seven dwarfs are missing. Snow White however finds a file, which contains useful information steganographically hidden. Help her to find the dwarfs.
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293 users have already solved this challenge, 84 are working on it.
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Reserve Hand Procedure — Part 1
Description
The reserve hand procedure has been used as a replacement of the Enigma machine. Can you decrypt the given ciphertext?
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194 users have already solved this challenge, 11 are working on it.
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Multilingual Monoalphabetic Substitution
Description
The plaintext consists of English, French, German and Italian words. Can you identify the four sentences after you have solved the monoalphabetic substitution?
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78 users have already solved this challenge, 6 are working on it.
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Cascading Encryption — Part 1/3
Description
Can you break this cascading encryption that consists of a combination of substitution and transposition? The solution contains important information for the next parts.
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72 users have already solved this challenge, 2 are working on it.
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Enigma Messages
Description
Can you find the plaintext using 26 Engima ciphertexts that have been encrypted with different rotors and different initial settings?
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80 users have already solved this challenge, 5 are working on it.
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Playfair with hints about the grid
Description
In this challenge, only fragments of the grid used for a Playfair encryption are given. Are you able to reconstruct the matrix and decrypt the message?
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117 users have already solved this challenge, 6 are working on it.
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A hidden word
Description
This PDF file is supposed to contain a hidden codeword. Can you find it?
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843 users have already solved this challenge, 166 are working on it.
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Strange Message from Thessaloniki
Description
This postcard from Thessaloniki was written in German in 1897. The encrypted text can either be considered as message from the sailor Fritz to his wife at home, or as a note regarding spionage activities. Can you determine the codeword that was used to request secret information?
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51 users have already solved this challenge, 5 are working on it.
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Recycled One-Time Pad
Description
Can you decrypt the three military messages?
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67 users have already solved this challenge, 13 are working on it.
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Beaver Code
Description
The Beaver Code is a transposition cipher. Apart from the solution of this challenge, can you find a formula for any given ciphertext length, which generates the permutation needed to decrypt the ciphertext?
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1199 users have already solved this challenge, 44 are working on it.
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Letter to the Templars — Part 2
Description
Can you decrypt the second part of the letter to the Templars as effortlessly as the first one?
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828 users have already solved this challenge, 12 are working on it.
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Letter to the Templars — Part 1
Description
After the Order of the Templar has become very powerful, enviers try to crush it. The knights receive an encrypted letter but the key does not arrive. Does this letter contain the warning that would have saved the knights from being arrested?
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1032 users have already solved this challenge, 43 are working on it.
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An 'unhearable' message
Description
Your friend sent you an audio file that contains only a strange melody. In the email, your friend writes that the file contains a message encoded by a variant of Morse code. Can you find out how you can hear the Morse code?
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41 users have already solved this challenge, 19 are working on it.
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How do you become a big cryptographer?
Description
You are invited to a job interview for the job of a cryptographer. Can you pass the first selection round?
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227 users have already solved this challenge, 106 are working on it.
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Number Sequence — Part 5
Description
How are the numbers linked? Can you find the three missing numbers?
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98 users have already solved this challenge, 130 are working on it.
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Number Sequence — Part 4
Description
Can you find the link between these numbers?
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845 users have already solved this challenge, 22 are working on it.
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¿No Hablas Español? No problemo!
Description
You don't speak Spanish? No Problem! Try to decrypt a ciphertext in a foreign language without knowledge of that language.
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166 users have already solved this challenge, 17 are working on it.
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Number Sequence — Part 3
Description
This number sequence is cyclic. Can you find out the fifth and sixth number?
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1022 users have already solved this challenge, 105 are working on it.
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The Book Code: A Challenge for Bookworms
Description
In order to decrypt the intercepted letter addressed to your neighbor, you need to find out which document has been used to encode the message with the book code.
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152 users have already solved this challenge, 27 are working on it.
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ECDH-Key Exchange for Beginners
Description
Alice and Bob would like to agree upon a shared key. They use an Elliptic Curve Diffie-Hellman (ECDH) key-exchange protocol. Try to reproduce the steps that are necessary to calculate the key and to decrypt Bob's message.
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98 users have already solved this challenge, 2 are working on it.
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Monoalphabetic substitution with camouflage — Part 4
Description
Alice and Bob use the cipher as it had been described in part 3 of this challenge. Due to an error one message has been encrypted and sent twice. Does this help you to find out the shared key and enables you to decrypt a third message easily?
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50 users have already solved this challenge, 5 are working on it.
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Monoalphabetic substitution with camouflage — Part 1
Description
It is not difficult to break a monoalphabetic substitution but in this challenge an additional camouflage alphabet causes confusion.
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65 users have already solved this challenge, 8 are working on it.
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Factorization Cipher — Part 1
Description
With the help of 7 pairs of plaintext-ciphertext you have to find out how this factorization cipher works and then decrypt a ciphertext.
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500 users have already solved this challenge, 16 are working on it.
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Turing Bombe Enigma I
Description
You intercepted two ENIGMA I messages. Both are dated from the same day. Use a Turing Bombe to find out the key of the day and decipher the solution.
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71 users have already solved this challenge, 3 are working on it.
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An Invisible Message
Description
A friend of yours sent you a file that seems to be empty. Was it just a mistake or is there a secret to reveal?
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59 users have already solved this challenge, 17 are working on it.
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Grille Cipher
Description
You need to reconstruct some fields of the grille to decrypt the message written on an old note.
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490 users have already solved this challenge, 41 are working on it.
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Double Columnar Transposition
Description
Asterix and Obelix besiege Rome. They just happened to find an encrypted message but instead of the common Caesar Cipher the Romans used a new method. Can you decrypt the message?
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117 users have already solved this challenge, 2 are working on it.
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Affine Codes / Modulo Arithmetic with N / Extended Euclid
Description
Two girls want to communicate in a secret way using the „affine cipher“. Transform the encryption rule into the decryption rule and turn in the plaintext of the example.
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595 users have already solved this challenge, 11 are working on it.
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Pigpen with a twist — Part 1
Description
In this challenge the rotational relationship between the Pigpen symbols are used to create a new cipher. In this part the well-known key squares are used as a warm up.
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155 users have already solved this challenge, 7 are working on it.
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Modified Caesar Cipher
Description
The Caesar Chiper is rather simple. But in this challenge it is used with a different alphabet and a modified way of shifting the letters.
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228 users have already solved this challenge, 60 are working on it.
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ADFGVX — Part 2
Description
A pair of plaintext and the corresponding ciphertext encrypted with the ADFGVX cipher ist given. Can you reveal the substitution and transposition key used in this example?
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123 users have already solved this challenge, 8 are working on it.
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ADFGVX — Part 1
Description
A small ciphertext encrypted with the ADFGVX cipher, which has been used during World War I, is given. Are you able to reveal the plaintext message?
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119 users have already solved this challenge, 15 are working on it.
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Number Sequence — Part 2
Description
This sequence is infinite, the first 9 numbers are given. What are the 10th and 11th number?
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2124 users have already solved this challenge, 482 are working on it.
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Music Code — Part 1
Description
A piece of music is given as mp3 file and in music notation. The notes represent a secret message, which was encrypted with two classic methods. In part 1 of this challenge you have to solve the first of these methods. Thereafter, you can set out to solve part 2 (which is in level 2).
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43 users have already solved this challenge, 30 are working on it.
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Post-Quantum Cryptography: Unbalanced Oil and Vinegar System — Part 1
Description
By the time quantum computers exist, the actual signing algorithms are not secure anymore. Then one can switch e.g. to so-called "Unbalanced Oil and Vinegar" systems. It is your challenge to break a simplified version of such a system today already.
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99 users have already solved this challenge, 2 are working on it.
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Kaskade-S/T — Part 1
Description
A friend sends you a cipher designed by him and asks you to discover the used key, using a given plaintext and the corresponding ciphertext.
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105 users have already solved this challenge, 8 are working on it.
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Playfair Encryption
Description
In this challenge you shall break the Playfair encryption which was used by the British forces in the Crimean War and in World War I, among others.
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124 users have already solved this challenge, 11 are working on it.
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Original Caesar Cipher
Description
In this challenge you shall break the Caesar encryption in its original form.
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3039 users have already solved this challenge, 145 are working on it.
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Enigma Combinatorics
Description
The Enigma is an electro-mechanical rotor machine used for encryption and decryption. One main part of the Enigma is changeable rotors. This challenge deals with the calculation of the key space.
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107 users have already solved this challenge, 63 are working on it.
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One-Time Pad with Flaws
Description
The "Three Investigators" heard that it was possible to create truly unbreakable cipher texts if you linked a stream of true random numbers to the plaintext (one-time pad). However this random stream must be incalculable for outsiders. Do you think you can, nevertheless, decrypt an eavesdropped encrypted message from the "Three Investigators"?
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311 users have already solved this challenge, 21 are working on it.
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Molehunt (Part 2/3)
Description
This is part 2 of a 3-part challenge regarding the classical transposition. You can solve this challenge with pen and paper as well as with different software programs. To create the ciphertext the plaintext was first encrypted with a classical shift cipher. The result of this encryption was then further encrypted with a columnar transposition with a key length of less than 10 characters.
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149 users have already solved this challenge, 7 are working on it.
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Molehunt (Part 1/3)
Description
This is part 1 of a 3-part challenge regarding the classical transposition. You can solve this challenge with pen and paper as well as with adequate software programs (e.g. CrypTool 2). With this irregular columnar tranposition a key length greater than 10 was used.
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158 users have already solved this challenge, 11 are working on it.
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A modified homophonic cipher with reduced alphabets — Part 2
Description
Homophonic substitution using 5 ciphertext characters for a binary cleartext alphabet. This challenge can be solved with paper & pencil.
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340 users have already solved this challenge, 8 are working on it.
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A modified homophonic cipher with reduced alphabets — Part 1
Description
Homophonic substitution using 3 ciphertext characters for a binary cleartext alphabet. This challenge can be solved with paper & pencil.
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394 users have already solved this challenge, 73 are working on it.
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Caesar Encryption
Description
The Caesar encryption, a very simple example of a monoalphabetic substitution.
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1455 users have already solved this challenge, 783 are working on it.
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Zodiac Cipher
Description
In the late 1960s the so called Zodiac killer used a homophonic substitution encryption to encrypt letters to the police and the press. This challenge is inspired by the solved Zodiac-408 problem and the unsolved Zodiac-340 problem. Hint: Provide the codeword in capital letters.
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100 users have already solved this challenge, 39 are working on it.
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Monoalphabetic Substitution
Description
This is a famous speech of a German soccer star - including a mistake. The codeword consists of 2 words, one after the other with no space. The first is the password used to encrypt the plaintext, and the second is the mistake in the decrypted text. (The plaintext is in German.)
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551 users have already solved this challenge, 181 are working on it.
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Number Sequence
Description
This sequence is infinite, but you may recognize it after just 13 numbers. What is the 14th number? Please type in the numeric expression of the number.
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4324 users have already solved this challenge, 430 are working on it.
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Letter from the Alleged Countess Julie von Ortenburg
Description
In 1806, the young countess Julie finds a dress with an old enciphered letter in a pouch. It reveals a secret of one of Julie's ancestors. Can you break the cipher? The codeword for this challenge is the last word of the letter (all uppercase).
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180 users have already solved this challenge, 19 are working on it.
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A Secret Message from Castle Mansfeld
Description
In September 1902, a book seller named Paul Winkler received a postcard in cipher. Sent from the nearby Mansfeld castle, it appears that a young lady wants to meet with Paul – secretly. Find the name of the young lady and submit it as the codeword for this challenge. Use only capital letters.
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130 users have already solved this challenge, 19 are working on it.
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Classical Ciphers^3
Description
This challenge contains three messages encrypted with classical ciphers. You will need break each of the ciphers and take note of the three codewords. When you have all three codewords, submit them in the form "codeword1-codeword2-codeword3". Please note that the codewords are case sensitive and you have only 5 trials to find the correct solution. The MTC3 team wishes everybody much success and fun in finding the correct solution.
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