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Challenge "Purple 1"  

  By: admin on Oct. 27, 2010, 7:09 p.m.

The Purple machine was the Japanese counterpart of the German Enigma machine. Decrypt the given ciphertext which was encrypted with the Purple machine.
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 Last edited by: admin on Oct. 31, 2021, 2:54 a.m., edited 1 time in total.

Re: Challenge "Purple 1"  

  By: yosh on Oct. 29, 2010, 4:26 p.m.

Hi,

i don't get the part with the initial permutation.
Does it really mean that i have to test all 26! permutations of the alphabet A-Z ???
Together it would be about (26! = ~10^26,605) * 6 * 24^4, right?
That seems to be a little bit too much for level 2 or at least for my old notebook…?!
Am i missing something obvious?

Regards

Re: Challenge "Purple 1"  

  By: stamp on Oct. 30, 2010, 12:05 a.m.

Hi,

i don't get the part with the initial permutation.
Does it really mean that i have to test all 26! permutations of the alphabet A-Z ???
Together it would be about (26! = ~10^26,605) * 6 * 24^4, right?
That seems to be a little bit too much for level 2 or at least for my old notebook…?!
Am i missing something obvious?

Regards

You don't want to try an exhaustive search, since (as you've noted) that's never going to finish. There is a shortcut, which depends on the fact that if a putative alphabet permutation is "close" to the actual permutation, then the putative plaintext is "close" to the actual plaintext.

Problems with the format of the solution...  

  By: jomandi on Nov. 11, 2011, 10:03 p.m.

I have decrypted the text and have the plaintext, permutations, initial positions, …

The problem is, that the system does not accept the solution. I have tried some variants, because the format of solution is not clear for me.

  1. initial permutation:
    do you mean the "input permutation", or the "inverted input permutation (like in the c program)"?

  2. order of the 3 stepping switches:
    which order? fast-medium-slow, slow-medium-fast, …

  3. initial position of all of the 4 switches:
    in which order? LMRS, SLMR, …
    in which range? from 0 to 24 (like in the c-program) or from 1 to 25

Can anyone check my solutions resp. help me to clarify the problems?

Thanks, jomandi

PS.: Unlike in the challenge text stated, the switches have only 25 initial positions (and not 26) and can therefore not be mapped directly from A to Z.

Re: Problems with the format of the solution...  

  By: be on Nov. 13, 2011, 9:09 p.m.

Can anyone check my solutions resp. help me to clarify the problems?
Thanks, jomandi

We'll check with the author. Please give us some days.

Re: Problems with the format of the solution...  

  By: stamp on Nov. 14, 2011, 3:04 a.m.

I have decrypted the text and have the plaintext, permutations, initial positions, …

The problem is, that the system does not accept the solution. I have tried some variants, because the format of solution is not clear for me.

  1. initial permutation:
    do you mean the "input permutation", or the "inverted input permutation (like in the c program)"?

  2. order of the 3 stepping switches:
    which order? fast-medium-slow, slow-medium-fast, …

  3. initial position of all of the 4 switches:
    in which order? LMRS, SLMR, …
    in which range? from 0 to 24 (like in the c-program) or from 1 to 25

Can anyone check my solutions resp. help me to clarify the problems?

Thanks, jomandi

PS.: Unlike in the challenge text stated, the switches have only 25 initial positions (and not 26) and can therefore not be mapped directly from A to Z.

  1. That would be the inverted permutation, as in the C program
  2. Fast, medium, slow
  3. SLMR and everything is 0-based, so 0 to 24, not 1 to 25

Thanks for the comment in your "PS." That part of the description is definitely a bit confused. Fortunately, it doesn't directly affect the attack or solution.

Re: Challenge "Purple 1"  

  By: jomandi on Nov. 14, 2011, 8:01 a.m.

Now the solution is accepted.

Thanks for the help,
jomandi

Re: Challenge  

  By: Integral on March 6, 2014, 1:58 p.m.

Hi,

May I assume that the plain text is in English ?

Re: Challenge  

  By: aurelie on March 10, 2014, 9:19 a.m.

May I assume that the plain text is in English ?

Hello Integral,

I assume the plaintext is in English, however, I haven't stored it and the challenge is more than 3 years old so I'm not sure. I'm going to forward your question to the author.

Best regards,
Lena

Re: Challenge Purple  

  By: jomandi on March 10, 2014, 1:31 p.m.

May I assume that the plain text is in English ?

yes, the plain text is written in english.

best regards,
jomandi

Re: Challenge Purple  

  By: stamp on March 10, 2014, 5:08 p.m.

May I assume that the plain text is in English ?

yes, the plain text is written in english.

best regards,
jomandi

Yes, jomandi is correct—the plaintext is English.

Mark Stamp

Re: Challenge  

  By: Integral on March 13, 2014, 1:52 p.m.

thank you

Re: Challenge "Purple 1"  

  By: fmoraes on Dec. 4, 2014, 11:24 p.m.

Do I need to worry about the SIXES and TWENTY's or those are fixed like in the program? Seems like on a real Purple machine, we would have to find the sixes and the sixes switch and then do an attack on the twenties, but I am not clear if that is required or not for this challenge.

Seems like I should use the program as a basis with fixes 6/20 and find the settings and plugboard, but want some confirmation before I put some effort into that.

Re: Challenge "Purple 1"  

  By: fmoraes on Dec. 4, 2014, 11:43 p.m.

Never mind, I did a quick experiment with the tool from Cryptologia and a minor change to the code and the right settings (once I read the comment in the text) gave me the solution. It was just a matter of cleaning it up.

Re: Challenge "Purple 1"  

  By: be on Dec. 11, 2014, 3:51 a.m.

Could you be a bit more precise what tool you used and what hint/comment was helpful to you. Maybe, this information is helpful for others too. Thanks, be


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