On Sept. 4, 2022, 10:11 a.m.
The historical Hill cipher uses matrix-vector multiplications to encrypt blocks
of letters. Can you find the inverse matrix and recover the plaintext?
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On May 14, 2022, 12:22 p.m.
A more difficult and even more interesting sequel to the "Alberti Challenge - Part 1".
Will you manage to crack this puzzle this time as well?
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On March 26, 2022, 8:45 p.m.
This challenge is about one of the oldest polyalphabetic ciphers.
Can you crack this centuries-old puzzle?
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On Jan. 24, 2022, 11:56 a.m.
This cipher is a new take on the well-known Vigenère cipher. It has been
designed to fix its "brother's" weaknesses. Can you find another weakness?
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On Oct. 31, 2021, 2:22 p.m.
Hello everyone,
As many of you might have noticed, our website has become very slow over the last months. These slowdowns were mainly caused by the aging code…
On Oct. 6, 2021, 11:51 a.m.
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 w…
On Oct. 6, 2021, 11:47 a.m.
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 challenge…
On July 31, 2021, 6:03 p.m.
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 w…
On July 31, 2021, 5:58 p.m.
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 w…
On July 31, 2021, 5:47 p.m.
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 w…
On June 1, 2021, 1:45 p.m.
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 wi…
On June 1, 2021, 1:35 p.m.
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 wi…
On June 1, 2021, 1:18 p.m.
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 wi…
On May 21, 2021, 3:10 p.m.
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 r…
On April 21, 2021, 7:17 p.m.
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 g…