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Challenge "The Josse Challenge – Part 1"  

  By: admin on Feb. 10, 2023, 8:47 a.m.

The Josse cipher is a polyalphabetic cipher from the time of the Franco-Prussian War. Its description was lost. It was only rediscovered and published in 2020. In these challenges you are to decipher several, increasingly shorter ciphertexts.
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Re: Challenge "The Josse Challenge – Part 1"  

  By: Theofanidis on Feb. 10, 2023, 3:24 p.m.

Dear MTC3 team. Two short comments regarding this challenge : 1. In both pdfs (English and German translation), there is an obvious typographic error, which i checked it with the CT2 challenges template rationale) : In slide 6/8, the 3rd rule should be corrected from Ci = (Pi + Ci-1) mod' 25, to Ci = (Ci + Ci-1) mod' 25. 2. While it is stated that the alphabet does not contain W, in CT2 template, it is included. Kind Regards, George Theofanidis

Re: Challenge "The Josse Challenge – Part 1"  

  By: newton on Feb. 10, 2023, 3:27 p.m.

Hi,

thanks for the information, we're looking into it.

Re: Challenge "The Josse Challenge – Part 1"  

  By: NiKo on Feb. 10, 2023, 3:57 p.m.

Hi George,

Concerning your remarks :-)

1) Equation:

Concerning the equation: Given in the slides: ci = pi + c(i-1) mod' 25 You want to correct it to: ci = ci + c(i-1) mod' 25

Please have a look here, you don't have ci but you want to comput it. So this is not possible with your equation. In each step after the first two, Josse encrypted each plaintext letter using the previous ciphertext letter: ci = pi + c(i-1) mod' 25

2) Concerning the alphabet:

Yes, you are right. The original Josse cipher uses a 25-letter alphabet (excluding the W). The CT2 component is a bit more flexible. The default the component uses is the 25-letter alphabet, but the component allows to provide your own alphabet. And the template provides an alphabet with 26 letters (including W). We added the W in the template's alphabet to allow the W in "world" being encrypted. In the challenges, we used a 25-letter alphabet as described and as Josse used. If you want to use the CT2 template and it should work as the original cipher, you can either delete the W from the alphabet or delete the TextInput component providing the alphabet.

Greetings, Nils

Re: Challenge "The Josse Challenge – Part 1"  

  By: Theofanidis on Feb. 10, 2023, 5:54 p.m.

Dear Nils, Thanks for the clarification. IMHO the only "misleading" text is the following that is included in the CT2 Josse cipher template : "These numbers are then encrypted using the equation Ci = (Pi-1 + P_i) mod len(alphabet)." Kind Regards, George Theofanidis

Re: Challenge "The Josse Challenge – Part 1"  

  By: NiKo on Feb. 10, 2023, 9:20 p.m.

Hey George! Yes, I see. Good spot, thx. I fixed that in the CT2 template and also updated the alphabet and plaintext to the original Josse version in the template. We have now "vvorld" instead of "world". The fix is available in the CT2 nightly build of tomorrow. Greetings, Nils

Re: Challenge "The Josse Challenge – Part 1"  

  By: madness on Feb. 17, 2023, 3:47 a.m.

Hello, everyone.

I did not receive an email to let me know that this new challenge had been posted. I thought I was subscribed to the relevant things, but perhaps not. How can I arrange it so that I receive an email whenever a new challenge is added?

Thank you.

Re: Challenge "The Josse Challenge – Part 1"  

  By: madness on Feb. 25, 2023, 3:28 a.m.

I did as you instructed. I found that I was already subscribed for new challenges. But I "saved changes" anyway.

The Josse 2 challege has appeared on the website. However, I did NOT receive an email announcement. Can this be fixed? Thank you.

Re: Challenge "The Josse Challenge – Part 1"  

  By: newton on Feb. 25, 2023, 9:12 a.m.

Hi madness,

do you receive other MTC Email (i.e., Forum replies)?

 Last edited by: newton on Feb. 25, 2023, 9:12 a.m., edited 1 time in total.

Re: Challenge "The Josse Challenge – Part 1"  

  By: NiKo on Feb. 25, 2023, 9:26 a.m.

Hey madness, which email provider do you use? With my private mailserver, since I host it using AWS (amazon web services), hotmail for example refuses to talk. It may be also a problem with the provider which filters out mails from this domain/our server. Greetings, Nils

 Last edited by: NiKo on Feb. 25, 2023, 9:27 a.m., edited 2 times in total.

Re: Challenge "The Josse Challenge – Part 1"  

  By: madness on Feb. 25, 2023, 3:46 p.m.

I am so embarrased. Please disregard everything. My email wasn't being forwarded. All the notifications are there on the other account. So sorry, and thank you.

Re: Challenge "The Josse Challenge – Part 1"  

  By: madness on March 23, 2023, 8:54 p.m.

Did anyone notice that Josse's way of mixing the alphabet is the same one used by Wheatstone? It must have been a popular method at the time.

Edit: except for the part about handling repeated letters

 Last edited by: madness on March 24, 2023, 9:02 p.m., edited 1 time in total.

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