Challenge "A modified homophonic cipher with reduced alphabets — Part 2"  

  By: admin on Oct. 21, 2010, 4:22 p.m.

Homophonic substitution using 5 ciphertext characters for a binary cleartext alphabet. This challenge can be solved with paper & pencil.

 Last edited by: admin on Oct. 31, 2021, 2:54 a.m., edited 3 times in total.

Re: Challenge  

  By: MichaelF on Oct. 22, 2010, 5:06 p.m.

Ich bekomme hier eine Fehlermeldung beim Einsenden der Lösung:

Warning: fopen(/usr/local/www/apache22/data/cryptochallenge/logs/challenges.log) [function.fopen]: failed to open stream: No such file or directory in /usr/local/www/apache22/data/cryptochallenge/modules/mod_displayc3challenges/helper.php on line 104
can't open file

Irgendwie sollte der Post zu "Part 1". Vielleicht habe ich mich verklickt. Entschuldigung! Aber wie ich gerade beim erneuten Laden der Seite bemerkt habe, ist die Aufgabe von mir richtig gelöst worden. Falls das so bleiben sollte, hat sich mein Post wegen der Fehlermeldung zu "Part 1" hiermit erledigt. [HTML_REMOVED]

Re: Challenge  

  By: admin on Oct. 22, 2010, 6:05 p.m.

Thanks for the hint. Our log file was surprisingly gone. Bug removed.

Re: Challenge  

  By: joberlin on Nov. 1, 2010, 2:47 p.m.

Der ASCII-Code ist ein 7bit-Code.

Re: Challenge  

  By: be on Nov. 1, 2010, 5:57 p.m.

Der ASCII-Code ist ein 7bit-Code.

You are right – but the hint at the end of the challenge is also right: Its a hint not necessary to solve the challenge but to make yourself sure you got the right solution. The intent of the hint was to say that if you divide your solution in 8-bit blocks (bytes) and interpret the according integer value as ASCII you get a meaningful sentence. This is a correct wording. The challenge did not say, this is ASCII code.
See: and
ASCII includes definitions for 128 characters.
E.g. within the 8-bit code "Windows-1252" the assigned characters of its first 128 integer values are the same as in pure 7-bit ASCII code. At least for the integers used in this challenge.

Re: Challenge  

  By: Luy on Oct. 25, 2011, 10:30 p.m.

The hint is actually necessary to solve the challenge since one has to enter the codeword and not the binary sequence. This should maybe also be noted somewhere in the problem description (at least, it was not clear to me).

Re: Challenge  

  By: be on Oct. 26, 2011, 1:03 a.m.

This should maybe also be noted somewhere in the problem description

Thanks, we'll do.

Re: Challenge  

  By: hamster147 on Jan. 4, 2015, 11:47 p.m.

I have worked out the correct bigram frequencies and converted the ciphertext to what looks like a correct sentence, complete with spaces, punctuation and upper/lower case, but the answer is not accepted. Is it just the string of ASCII characters that is required?

Re: Challenge  

  By: Theofanidis on Jan. 5, 2015, 9:45 a.m.

Dear Hamster147

The SHA-256 of the plaintext is - according to Cryptool 1.4 Version

59 BC 14 DB 13 52 A3 33 58 7C CF DD 3A 1B CA 1E 45 84 1A 70 4C 8E 37 B7 E3 69 60 61 AB C2 EA 39

Best Regards
George Theofanidis

It should contain 39 characters that include Upper and lower case characters, spaces and punctuation marks

Re: Challenge  

  By: hamster147 on Jan. 5, 2015, 7:28 p.m.

Thanks George.

I re-checked my conversion from binary to ASCII and found a mistake, which actually makes more sense in English!

Best regards,


Re: Challenge  

  By: Thalhammer on Oct. 17, 2018, 5:58 p.m.

I actually had the correct solution for this one right from the beginning, but spent 7 tries until I noticed that I had to convert the zero and ones into characters [HTML_REMOVED]

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