All Challenges

343 published challenges (in level I, II, III and X), sorted by:
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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the last challenge in a series of 13 level-2 challenges with the SZ42. In this "key breaking" challenge you are provided with one ciphertext and parts of the corresponding plaintext. Can you find the MU wheel patterns and decrypt the ciphertext?

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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the twelfth challenge in a series of 13 level-2 challenges with the SZ42. In this "key breaking" challenge you are provided with one ciphertext and parts of the corresponding plaintext. Can you find the PSI wheel patterns and decrypt the ciphertext?

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Description
The SIGABA CSP-2900 was a highly secure encryption machine used by the US for strategic communication in WWII. In this series of challenges, you are provided with a ciphertext and a partially-known plaintext, here with the length of 200 and 100 characters.

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Description
The SIGABA CSP-2900 was a highly secure encryption machine used by the US for strategic communication in WWII. In this series of challenges, you are provided with a ciphertext and a partially-known plaintext, here with the length of 270 and 120 characters.

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Description
The SIGABA CSP-2900 was a highly secure encryption machine used by the US for strategic communication in WWII. In this series of challenges, you are provided with a ciphertext and a partially-known plaintext, here with the length of 320 and 120 characters.

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Description
The SIGABA CSP-889 was a highly secure encryption machine used by the US for strategic communication in WWII. In this series of challenges, you are provided with a ciphertext and a partially-known plaintext, here with the length of 200 and 100 characters.

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Description
The SIGABA CSP-889 was a highly secure encryption machine used by the US for strategic communication in WWII. In this series of challenges, you are provided with a ciphertext and a partially-known plaintext, here with the length of 270 and 120 characters.

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Description
The SIGABA CSP-889 was a highly secure encryption machine used by the US for strategic communication in WWII. In this series of challenges, you are provided with a ciphertext and a partially-known plaintext, here with the length of 320 and 120 characters. Update June 2021: We replaced the used key (and this changed the ciphertext) since a part of the previous used key was leaked in the newest SIGABA template of CrypTool 2.

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Description
The Wheatstone Cryptograph is a simple device that resembles a clock with two hands. For each hand there is a ring of symbols. In this challenge the key is a random permutation of the english alphabet. Are you able to decrypt the given ciphertext?

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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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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the eleventh challenge in a series of 13 level-2 challenges with the SZ42. In this "key breaking" challenge you are provided with one ciphertext and the corresponding plaintext. Can you find the wheel patterns?

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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the tenth challenge in a series of 13 level-2 challenges with the SZ42. In this "key breaking" challenge you are provided with one ciphertext and the corresponding plaintext. Can you find the wheel patterns? Update January 2021: The starting positions for the CHI wheels were added.

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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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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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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the ninth challenge in a series of 13 level-2 challenges with the SZ42. In this "setting" challenge you are provided with only one ciphertext; the patterns for all the wheels are known as well as the starting positions for the CHI wheels. Can you find the starting positions for both the MU and PSI wheels and decrypt the ciphertext?

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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the eighth challenge in a series of 13 level-2 challenges with the SZ42. In this "setting" challenge you are provided with only one ciphertext; the patterns for all the wheels are known as well as the starting positions for the CHI and PSI wheels. Can you find the starting positions for the MU wheels and decrypt the ciphertext?

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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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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the seventh challenge in a series of 13 level-2 challenges with the SZ42. In this "setting" challenge you are provided with only one ciphertext; the patterns for all the wheels are known as well as the starting positions for the CHI and MU wheels. Can you find the starting positions for the PSI wheels and decrypt the ciphertext?

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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the sixth challenge in a series of 13 level-2 challenges with the SZ42. In this "setting" challenge you are provided with only one ciphertext and the patterns for all five CHI wheels are known. Can you find the starting positions for the five CHI wheels?

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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the fifth challenge in a series of 13 level-2 challenges with the SZ42. In this "setting" challenge you are provided with only one ciphertext and the patterns for CHI1 and CHI2 wheels are known. Can you find the starting positions for CHI1 and CHI2?

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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the fourth challenge in a series of 13 level-2 challenges with the SZ42. In this "setting" challenge you are provided with only one ciphertext and the patterns for CHI1 and CHI2 wheels are known. Can you find the starting positions for CHI1 and CHI2?

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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the third challenge in a series of 13 level-2 challenges with the SZ42. Here, you are provided with 2 in-depth ciphertexts and a limitation is used. Can you recover the plaintexts?

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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the second challenge in a series of 13 level-2 challenges with the SZ42. Here, you are provided with 4 in-depth ciphertexts and a limitation is used. Can you recover the plaintexts?

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Description
The Lorenz SZ42, codenamed Tunny, was a German teleprinter encryption device used during WW2. This is the first challenge in a series of 13 Level-2 challenges with the SZ42. Here, you are provided with 8 in-depth ciphertexts. Can you recover the plaintexts?

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Description
This is part 3 of the challenge series about lattice-based cryptography schemes. This challenge introduces an encryption scheme which uses systems of linear equations. Can you decrypt a message without knowing the key?

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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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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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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of new heavier challenges with T52. In this challenge, you need to recover a plaintext from a T52E ciphertext and a crib. The key is partially known.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of new heavier challenges with T52. In this challenge, you need to recover a plaintext from a T52D ciphertext and a crib. The key is unknown.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of new heavier challenges with T52. In this challenge, you need to recover a plaintext from a T52AB ciphertext and a crib. The key is unknown.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of new heavier challenges with T52. In this challenge, you need to recover a plaintext from a T52D ciphertext and a crib. The key is partially known.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of new heavier challenges with T52. In this challenge, you need to recover a plaintext from T52D ciphertexts "in-depth". You are also provided with cribs for each message. The key is unknown.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of new heavier challenges with T52. In this challenge, you need to recover a plaintext from T52E ciphertexts "in-depth". You are also provided with cribs for each message. The key is partially known.

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Description
This part of the challenge series introduces polyhomophonic substitution. In a polyhomophonic substitution cipher, each ciphertext symbol can represent one of several plaintext symbols, and each plaintext letter can be encrypted as one of several ciphertext letters. The key is a mapping from the set of plaintext symbols to the set of ciphertext symbols.

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Description
The SIGABA was a highly secure encryption machine used by the US for strategic communications in WWII. As in the first five parts of this series of challenges, you are provided with a partial known-plaintext. However, in this part you get no information about the key.

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Description
This part of the challenge series is a warm-up with polyphonic substitution. In a polyphonic substitution cipher, more than one plaintext letter are encrypted to the same ciphertext symbol. The key is a mapping from the set of plaintext symbols to the set of ciphertext symbols.

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Description
The SIGABA was a highly secure encryption machine used by the US for strategic communications in WWII. As in the first four parts of this series of challenges, you are provided with a partial known-plaintext, and some information about the key settings. However, in this part you get even less information about the key.

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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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Description
The SIGABA was a highly secure encryption machine used by the US for strategic communications in WWII. As in the first three parts of this series of challenges, you are provided with a partial known-plaintext, and some information about the key settings. However, in this part you get even less information about the key.

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Description
The SIGABA was a highly secure encryption machine used by the US for strategic communications in WWII. As in part 1 and part 2 of this series of challenges, you are provided with a partial known-plaintext, and some information about the key settings. However, in this part you get even less information about the key.

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Description
The SIGABA was a highly secure encryption machine used by the US for strategic communications in WWII. As in part 1 of this series of challenges, you are provided with a partial known-plaintext, and some information about the key settings. However, in this part you get less information about the key.

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Description
The SIGABA was a highly secure encryption machine used by the US for strategic communications in WWII. It is believed that the German codebreakers were unable to make any inroads against SIGABA. In this part of the series of challenges, you are provided with a partial known-plaintext, and some information about the key settings.

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Description
LoRa calculates the ciphertext by using a logic expression as key. The ciphertext unusually contains large bitstreams too. Could you find the logic expression from a given ciphertext?

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Description
This challenge series introduces in detail the handling of the differential cryptanalysis (DCA). In the first two challenges you have to decrypt encrypted images and enter the code shown in the images. The second challenge requires filtering.

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Description
This is part two of the two polyphonic cipher challenges, where again two or more plaintext letters correspond to one cipher symbol. Can you solve such a cipher?

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Description
This challenge series introduces in detail the handling of the differential cryptanalysis (DCA). In the first two challenges you have to decrypt encrypted images and enter the code shown in the images. The first challenge needs no filtering, as only valid plaintext-ciphertext pairs are delivered.

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Description
In a polyphonic cipher, two or more plaintext letters correspond to one ciphertext symbol.

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Description
Determine which type of classic cipher was used to generate each of 500 ciphertext messages. The ciphers used in this challenge are simple substitution, columnar transposition, Vigenère, Playfair, and Hill.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of new heavier challenges with T52. In this challenge, you need to recover a plaintext from one T52C ciphertext. The key is unknown.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of new heavier challenges with T52. In this challenge, you need to recover a plaintext from one T52AB ciphertext. The key is unknown.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of new heavier challenges with T52. In this challenge, you need to recover the plaintexts from T52D ciphertexts "in-depth". The key is unknown.

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Description
Like the MONOALPHABETIC SUBSTITUTION WITH CAMOUFLAGE series of challenges, this two-part challenge considers a modification of the classic simple substitution cipher achieved by randomly introducing decoy characters into the ciphertext in encryption which are then ignored in decryption. In part 2, the plaintext is first divided into two parts, then each part will be encrypted separately.

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Description
Like the MONOALPHABETIC SUBSTITUTION WITH CAMOUFLAGE series of challenges, this two-part challenge considers a modification of the classic simple substitution cipher achieved by randomly introducing decoy characters into the ciphertext in encryption which are then ignored in decryption. In part 1, the cipher uses a key which devides the ciphertext alphabet into signal characters and noise characters.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext from a T52ca ciphertext. The key is partially known. You are also provided with a crib.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext from a T52c ciphertext. The key is partially known. You are also provided with a crib.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext from six "in-depth" ciphertexts built with T52ca. You are also provided with cribs for each message.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext from six "in-depth" ciphertexts built with T52a/b. You are also provided with cribs for each message.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext from six "in-depth" ciphertexts built with T52c. The key is partially known. You are also provided with cribs for each message.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext from ten "in-depth" ciphertexts built with T52ca. The key is partially known.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext from ten "in-depth" ciphertexts built with T52c. The key is partially known.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext from ten "in-depth" ciphertexts built with T52ab. The key is partially known.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext only from a T52ab ciphertext. The key is partially known.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext only from a T52d ciphertext. The key is partially known.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext only from a T52c ciphertext. The key is partially known.

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Description
The Siemens and Halske T52 was a family of German teleprinter encryption devices used during WW2. This challenge is part of a series of challenges with T52. In this challenge, you need to recover the plaintext only from a T52ab ciphertext. The key is partially known.

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Description
The Vatican owns some encrypted manuscripts waiting for decryption. Can you find the solution for an archive manuscript from 1539-1548?

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Description
The Vatican owns some encrypted manuscripts waiting for decryption. Can you find the solution for an archive manuscript from 1535/1536?

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Description
The Vatican owns some encrypted manuscripts waiting for decryption. Can you find the solution for a message from 1721?

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Description
Handycipher is a low-tech stream cipher, simple enough to permit pen-and-paper encrypting and decrypting of messages, while providing a significantly high level of security. Handycipher was first published in 2014 and further improved in 2015 and 2016. Part 10 of the Handycipher series presents the same challenge as Part 9 but with a different key choice. It is a ciphertext-only challenge.

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Description
Part 2 of the series "Handycipher made in love" is almost identical to Part 1 except that the solution you are asked for is the correct key that Alice used to produce the ciphertext rather than the short message embedded in the plaintext.

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Description
Homophonic encryption is a modified version of the monoalphabetic substitution: One plaintext symbol can be substituted by more than one ciphertext symbol. In part 4 of this series we consider a distribution of the homophones based on English language statistics like in part 2, but the alphabet doesn't contain the blank. This is a ciphertext-only challenge. Try to crack the ciphertext and extract a specific word from the plaintext.

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Description
Homophonic encryption is a modified version of the monoalphabetic substitution: One plaintext symbol can be substituted by more than one ciphertext symbol. In part 3 of this series every plaintext symbol has the same number of possible substitutions like in part 1, but the alphabet doesn't contain the blank. This is a ciphertext-only challenge. Try to crack the ciphertext and extract a specific word from the plaintext.

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Description
Homophonic encryption is a modified version of the monoalphabetic substitution: One plaintext symbol can be substituted by more than one ciphertext symbol. In part 2 of this series we consider a distribution of the homophones based on English language statistics. This is a ciphertext-only challenge. Try to crack the ciphertext and extract a specific word from the plaintext.

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Description
Homophonic encryption is a modified version of the monoalphabetic substitution: One plaintext symbol can be substituted by more than one ciphertext symbol. In part 1 of this series every plaintext symbol has the same number of possible substitutions. This is a ciphertext-only challenge. Try to crack the ciphertext and extract a specific word from the plaintext.

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Description
Strange things happen when you're in love. This challenge is about how the plaintext can be revealed when Handycipher is used in a wrong way.

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Description
What would Nostradamus do to make a mono-alphabetic substitution harder to break?

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Description
Solving this challenge is not as hard as finding the needle in a haystack, isn't it?

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Description
Once upon a time, there was a three-part challenge which was inspired by Kryptos and is based on a fairy tale. Can you solve this mysterious challenge?

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Description
Once upon a time, there was a three-part challenge which was inspired by Kryptos and is based on a fairy tale. Can you solve this mysterious challenge?

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Description
Once upon a time, there was a three-part challenge which was inspired by Kryptos and is based on a fairy tale. Can you solve this mysterious challenge?

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Description
On November 3rd, 1509, Catherine of Aragon wrote an encrypted letter to her father. What did she tell him?

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Description
Three messages were delivered — two encrypted, one in clear. Can you solve the puzzle?

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Description
You are given a part of a keystream, which was produced by a filter generator. Can you find the missing keystream bytes?

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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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Description
What do you know about modular sequences? Work it out.

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Description
Sniffing on the WiFi, you notice an ElGamal encrypted message. Are you able to compute it?

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Description
Buying a train ticket via credit card should not be a problem — actually. Can you solve the subset-sum problem to get your train?

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Description
During your summer job in an Austrian weekly magazine a mysterious letter arrives. Are you able to decrypt the message?

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Description
The challenges for the weakened ElsieFour serve as an exercise and use an intentionally weakened version of LC4. ElsieFour combines ideas of modern RC4 stream cipher, historical Playfair cipher and plaintext-dependent keystreams. It can be computed manually. Part 2 is a partly-known key challenge which provides 12 consecutive characters of the key.

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Description
The challenges for the weakened ElsieFour serve as an exercise and use an intentionally weakened version of LC4. ElsieFour combines ideas of modern RC4 stream cipher, historical Playfair cipher and plaintext-dependent keystreams. It can be computed manually. Part 1 is a partly-known key challenge which provides the first 12 characters of the key.

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Description
How many experience points does Thomas need to reach the 200th level of his new computer game?

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Description
The Secret Archives of the Vatican keep a large collection of ciphertexts from papal correspondence. The keys of these manuscripts have been destroyed, or are kept elsewhere and been forgotten. Can you find out how to decipher the letter from March 14, 1625?

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The solution for this challenge was made public on June 20, 2018, 12:26 a.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.

Description
The Main Library of the Vatican owns some encrypted manuscripts, waiting for decryption. Can you find the solution to the letter from 1628?

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Description
The hero of the book has to decode a manuscript — seven lines of it are here for you. These lines were encoded with a mixture of classic methods — anagrams, two position-dependent monoalphabetic substitutions and Atbash. Can you help him?

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Description
What do you do, if your father and your stepmother decide to communicate only encrypted? You tape-record the messages. But what do the two of them really talk about?

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Description
Decrypting a Christmas carol to help children in need? It's not that easy, if you don't know much about cryptography. Can you help Jacob and the children?

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Description
Do you believe that AES is easy to break because of a wrong encoding? Try it yourself...

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Description
Mike would like to belong to the cryptographers. Can you help him to find out their meeting point at the Christmas market?

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Description
Little Anna has forgotten how to decrypt her ciphertext. Can you come up to her pre-Christmas wish?

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Description
Are you able to crack the password of Radomil and find the missing 5 digits?

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Description
Hilly is an improved version of Hill cipher. This challenge consists of the decryption of a ciphertext by means of a partly-known key.

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Description
The challenges for the weakened ElsieFour serve as an exercise and use an intentionally weakened version of LC4. ElsieFour combines ideas of modern RC4 stream cipher, historical Playfair cipher and plaintext-dependent keystreams. It can be computed manually. Part 3 is a partly-known-plaintext challenge which provides 2 messages that were encrypted with the same key.

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Description
ElsieFour combines ideas of modern RC4 stream cipher, historical Playfair cipher and plaintext-dependent keystreams. It can be computed manually. Part 1 is a partly-known-plaintext challenge which provides 2 messages that were encrypted with the same key.

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Description
From a honeypot you get a set of encrypted files and the according plaintext files. Could you discover the used key, to help victims of the ransom ware?

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Description
Holographic encryption can be performed by employing encryption masks which alter the field before propagation. This makes the image unrecognizable when recorded. You are given three holograms that represent the cipher image and three plain images and their holograms which were encrypted with the same encryption masks.

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Description
Holographic encryption can be performed by employing encryption masks which alter the field before propagation. This makes the image unrecognizable when recorded. You are given three holograms that represent the cipher image and two corrupted encryption masks.

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Description
Hilly is an improved version of the Hill cipher. This challenge consists of the decryption of a ciphertext by means of a given plaintext-ciphertext pair.

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Description
Handycipher is a newly created cipher designed to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security. Part 9 is the same as Part 6, but uses an improved version of the cipher. It is a ciphertext-only challenge.

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Description
Handycipher is a newly created cipher designed to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security. Part 8 is the same as Part 5, but uses an improved version of the cipher. You are given the ciphertext and 229 letters occuring at an unknown location in the plaintext.

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Description
Handycipher is a newly created cipher designed to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security. Part 7 is the same as Part 4, but uses an improved version of the cipher. You are given the ciphertext and the first 229 letters of the plaintext.

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Description
This series consists of 5 challenges based on each other. It introduces a new three-step cipher called ASAC, which is a modified version of ADFGVX. Part 5 is a "bonus" and just modifies the second challenge of this series by improving the second step of the cipher.

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Description
This series consists of 5 challenges based on each other. It introduces a new three-step cipher called ASAC, which is a modified version of ADFGVX. Part 4 uses the complete cipher and is the main challenge of this series.

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Description
This series consists of 5 challenges based on each other. It introduces a new three-step cipher called ASAC, which is a modified version of ADFGVX. Part 3 involves the complete cipher but weakens the third step by using a single-column transposition instead of a double column transposition.

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Description
This series consists of 5 challenges based on each other. It introduces a new three-step cipher called ASAC, which is a modified version of ADFGVX. Part 2 uses only the first two steps of the cipher.

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Description
This series consists of 5 challenges based on each other. It introduces a new three-step cipher called ASAC, which is a modified version of ADFGVX. Part 1 is meant as an introduction and uses only the first step of ASAC.

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Description
The Weakened Handycipher challenges serve as an exercise and use an intentionally weakened version of Handycipher. Part 6 is the same as Part 3, but uses an improved version of the cipher. It is ciphertext-only.

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Description
The Weakened Handycipher challenges serve as an exercise and use an intentionally weakened version of Handycipher. Part 5 is the same as Part 2, but uses an improved version of the cipher. It is ciphertext-only, but you are given some partial information about the key.

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Description
The Weakened Handycipher challenges serve as an exercise and use an intentionally weakened version of Handycipher. Part 4 is the same as Part 1, but uses an improved version of the cipher. You are given the first 1,009 characters of the plaintext, and some partial information about the key.

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Description
Extended Handycipher is an enhancement of Handycipher. Part 6 is the same as Part 3, but uses an improved version of the cipher. You are given two encryptions of the plaintext generated with the same key. It is ciphertext-only.

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Description
Extended Handycipher is an enhancement of Handycipher. Part 5 is the same as Part 2, but uses an improved version of the cipher. You are given two encryptions of the plaintext generated with the same key, and 229 characters occuring at an unknown location in the plaintext.

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Description
Extended Handycipher is an enhancement of Handycipher. Part 4 is the same as Part 1, but uses an improved version of the cipher. You are given three encryptions of the plaintext generated with the same key, and the first 229 characters of the plaintext.

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Description
Handycipher is a newly created cipher designed to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security. Part 6 is the same as Part 3, but uses an improved version of the cipher. It is a ciphertext-only challenge.

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Description
Handycipher is a newly created cipher designed to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security. Part 5 is the same as Part 2, but uses an improved version of the cipher. You are given the ciphertext and 229 letters occuring at an unknown location in the plaintext.

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Description
Handycipher is a newly created cipher designed to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security. Part 4 is the same as Part 1, but uses an improved version of the cipher. You are given the ciphertext and the first 229 letters of the plaintext.

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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 is the last part and teaches us something about the weaknesses of this method by improving it a little bit in some points.

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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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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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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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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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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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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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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 3 is a ciphertext-only challenge for which the second permutation key is known.

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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 2 is a ciphertext-only challenge for which the first permutation key is known.

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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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Description
How are the numbers interconnected? Can you find the three missing numbers?

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Description
Spirale is a OTP cipher designed to be simply performed by hand. Part 4 is a ciphertext-only challenge with a 485-letter ciphertext. Unlike the other three parts of this series, this one uses four new random keys.

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Description
Spirale is a OTP cipher designed to be simply performed by hand. Part 3 is a ciphertext-only challenge with a 949-letter ciphertext. In this part, two of the four keys are equal to the keys of the first two parts.

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Description
Spirale is a OTP cipher designed to be simply performed by hand. Part 2 is a ciphertext-only challenge with a 659-letter ciphertext. This part uses the same four keys for encryption as part 1 does.

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Description
Spirale is a OTP cipher designed to be simple to implement by hand. It is resilient to errors as they have only a local effect without obscuring all the ciphertext. Part 1 is a partly-known plaintext challenge with a 314-letter ciphertext. The first 75 letters of the plaintext are known. Part 2 of this series uses the same four keys as this one.

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Description
During the cold war the foreign intelligence agency of Germany established so-called stay-behind units. Their radio messages were encrypted by a OTP method, but the keys were used multiple times. This challenge is about the effect of this multiple usage on the security of the method. You are given 5 messages, all encrypted with the same key.

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Description
This challenge series is about the GRANIT cipher, a method that can be done manually. It has been used for instance by the former GDR spy Günter Guillaume till about 1960. Part 1, 2 and 3 of this series use the same keyword for generating the key matrix, but different permutation keys. This part has a ciphertext-only challenge and the ciphertext has 80 characters.

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Description
This challenge series is about the GRANIT cipher, a method that can be done manually. It has been used for instance by the former GDR spy Günter Guillaume till about 1960. Part 1, 2 and 3 of this series use the same keyword for generating the key matrix, but different permutation keys. This part has a ciphertext-only challenge and the ciphertext has 110 characters.

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Description
This challenge series is about the GRANIT cipher, a method that can be done manually. It has been used for instance by the former GDR spy Günter Guillaume till about 1960. Part 1, 2 and 3 of this series use the same keyword for generating the key matrix, but different permutation keys. In this part a codebook is used additionally, and the given ciphertext has 70 characters.

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Description
The challenges for the weakened Handycipher serve as an exercise and use an intentionally weakened version of Handycipher. Part 3 is a ciphertext-only challenge. Handycipher is a newly designed cipher to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security.

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Description
The challenges for the weakened Handycipher serve as an exercise and use an intentionally weakened version of Handycipher. Part 2 is a ciphertext-only challenge with a helping additional information. Handycipher is a newly designed cipher to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security.

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Description
The challenges for the weakened Handycipher serve as an exercise and use an intentionally weakened version of Handycipher. Part 1 is a partially-known-plaintext challenge with a helping additional information. Handycipher is a newly designed cipher to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security.

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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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Description
Extended Handycipher is an enhancement of the newly designed cipher Handycipher, which permits pen-and-paper encrypting and decrypting, while providing a significantly high level of security. You got only two different ciphertexts of the 996-character plaintext.

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Description
Extended Handycipher is an enhancement of the newly designed cipher Handycipher, which permits pen-and-paper encrypting and decrypting, while providing a significantly high level of security. From the 905-character plaintext 229 characters somewhere in it are known.

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Description
Extended Handycipher is an enhancement of the newly designed cipher Handycipher, which permits pen-and-paper encrypting and decrypting, while providing a significantly high level of security. From the 815-character plaintext the first 229 characters are known.

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Description
How are the numbers linked? Can you find the two missing numbers?

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Description
How are the numbers linked? Can you find the two missing numbers?

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Description
Handycipher is a newly designed cipher to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security. You got only the ciphertext of the 993-character plaintext.

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Description
Handycipher is a newly designed cipher to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security. From the 1142-character plaintext 229 characters somewhere in it are known.

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Description
Handycipher is a newly designed cipher to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security. From the 858-character plaintext the first 229 characters are known.

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Description
This is part 4 in a series about the M-138. Part 4 is a ciphertext-only challenge (75 letters).

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Description
This is part 3 in a series about the M-138. Part 3 is a ciphertext-only challenge (125 letters).

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Description
This is part 2 in a series about the M-138. Part 2 is a partly-known plaintext challenge (48/100).

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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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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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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 and 2 at first.

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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.

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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.

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Description
In the last part of a series of mid-level Double Column Transposition challenges, you have to find the two keys. Each of it is 19 characters long and has been derived from an English phrase.

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Description
In this part of a series of mid-level Double Column Transposition challenges, the keys that has been used for both transposition are given. Find out from which phrases they have been derived!

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Description
In this part of a series of mid-level Double Column Transposition challenges, the same key has been used for both transposition. This allows you to attack this simple, yet strong cipher.

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Description
In this part of a series of mid-level Double Column Transposition challenges, a large part of the beginning of the plaintext is known. This partial crib allows you to attack this simple, yet strong cipher.

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Description
The ORYX stream cipher consists of three 32-bit LFSRs X, A, B which are shifted differently depending on some bits in the LFSR X. The key stream is a combination of the highest 8 bits of each of the three LFSRs. It is neither feasible nor necessary to search the whole 96-bit key space, there are more efficient methods!

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Description
The ORYX stream cipher consists of three 32-bit LFSRs X, A, B which are shifted differently depending on some bits in the LFSR X. The key stream is a combination of the highest 8 bits of each of the three LFSRs. It is neither feasible nor necessary to search the whole 96-bit key space, there are more efficient methods!

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Description
The ORYX stream cipher consists of three 32-bit LFSRs X, A, B which are shifted differently depending on some bits in the LFSR X. The key stream is a combination of the highest 8 bits of each of the three LFSRs. It is neither feasible nor necessary to search the whole 96-bit key space, there are more efficient methods!

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Description
In this part of a series of mid-level Double Column Transposition challenges keys shorter than 20 allow you to attack this simple, yet secure cipher.

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Description
Many telegrams that date from the Spanish Civil War (1936 - 1939) still remain undisclosed. It is assumed that these telegrams were encrypted using the Spanish Strip Cipher. Try to find the plaintext of this original telegram.

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Description
An English telegram was encrypted using the Spanish Strip Cipher, a popular algorithm during the Spanish Civil War. It is your task to find the plaintext.

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Description
A Spanish telegram was encrypted using the Spanish Strip Cipher, a popular algorithm during the Spanish Civil War. It is your task to find the plaintext.

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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?

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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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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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Description
The double columnar transposition is considered to be one of the best manual encryption systems. This sequence considers vulnerabilities that have been used to solve the corresponding level X challenge. The three challenges of the sequence have an increasing difficulty. In the third part a German plaintext has been encrypted with random keys.

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Description
The double columnar transposition is considered to be one of the best manual encryption systems. This sequence considers vulnerabilities that have been used to solve the corresponding level X challenge. The three challenges of the sequence have an increasing difficulty. In the second part two interleaved English texts have been encrypted with random keys.

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Description
The double columnar transposition is considered to be one of the best manual encryption systems. This sequence considers vulnerabilities that have been used to solve the corresponding level X challenge. The three challenges of the sequence have an increasing difficulty. In the first part an English plaintext has been encrypted with keys derived from English sentences.

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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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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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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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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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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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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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Description
This challenge descends from the RSA Laboratories contest to encourage research into the practical difficulty of factoring large integers of different length (between 330 and 2048 bit) and cracking RSA keys used in cryptography. This challenge is about factoring a number with 212 decimal digits.

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The solution for this challenge was made public on July 31, 2013, 4:34 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.

Description
The ORYX stream cipher consists of three 32-bit LFSRs X, A, B which are shifted differently depending on some bits in the LFSR X. The key stream is a combination of the highest 8 bits of each of the three LFSRs. It is neither feasible nor necessary to search the whole 96-bit key space, there are more efficient methods!

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Description
The ORYX stream cipher consists of three 32-bit LFSRs X, A, B which are shifted differently depending on some bits in the LFSR X. The key stream is a combination of the highest 8 bits of each of the three LFSRs. It is neither feasible nor necessary to search the whole 96-bit key space, there are more efficient methods!

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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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Description
A new and unknown rotor has been added to the Typex machine. Use a known-plaintext attack to determine the wiring of the new rotor.

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Description
Use the hints from the first and second part of this challenge to decrypt this message that has been encrypted using an ENIGMA.

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Description
After solving the first part of this challenge, you can use the hints you found to decrypt the two ciphertexts that have been encrypted using the ADFGVX cipher.

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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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Description
The Typex cipher has been used in World War 2 as an alternative to the Enigma cipher. Find the key that was used in this challenge.

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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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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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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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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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Description
This PDF file is supposed to contain a hidden codeword. Can you find it?

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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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Description
Can you decrypt the three military messages?

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Description
Can you decrypt the last part of the letter and read the friend's advice?

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Description
Help Alice and Bob to find a treasure on the island Mallorca. For this purpose, a three-stage cipher needs to be broken.

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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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Description
Can you decrypt the second part of the letter to the Templars as effortlessly as the first one?