Challenge "Double Column Transposition Reloaded — Part 1"  

  By: admin on Dec. 11, 2013, 8:09 p.m.

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.

Re: Challenge  

  By: Veselovský on Dec. 18, 2013, 2:12 p.m.

Is a simple columnar transposition considered as easy to solve?
Why not first try to test simple columnar transposition and then double?
What is more secure, to use double columnar transposition with both key lengths around 20 or simple columnar transposition with one key of length around 33 to 40?

I think the simple columnar transposition would be more secure with such lengths of the keys, or am I missing something?

Re: Challenge  

  By: george4096 on Dec. 19, 2013, 2:09 a.m.

Hi Victor

Based on research recently done (eventually leading to the solution of the original Double Transposition Challenge X), we can say the following:

1) A single transposition cipher with key length of 33-40 is very easy to solve if the transposition rectangle is complete, and moderately easy if incomplete.

2) A double transposition cipher with length > 20 is very difficult to solve.

3) In the past (in the book by Wayne Barker, Cryptanalysis of the Double Transposition Cipher, the analysis is also available here it was shown that every double transposition can be expressed as a single transposition with key length equal to the PRODUCT of the lengths of the keys of the Double Transposition. But this wont help here because it is very difficult to solve a Single Transposition cipher with a key of ~500 length. And more specifically, the ciphertext is not long enough as you will have only about 1-2 rows in the transposition cipher. You need more "depth" to solve a single transposition cipher, even with much shorter keys.

Hope this helps

Re: Challenge  

  By: Veselovský on Dec. 19, 2013, 12:50 p.m.

Thank you for your explanation.

I would say, give me an algorithm which can quickly solve SCT (simple columnar transposition regular or irregular) of key length up to 40 and I can adapt it to solve any DCT (Double columnar transposition) with both key lengths up to 20. In theory it should work, but since I do not have an algorithm that can solve SCT with key length up to 40 very fast I can not verify it.

But I got simple algorithm that can solve SCT with key length up to about 16 pretty fast and I easily adapted it to solve DCT of both key lengths up to 8. So I think my method should work also for longer keys, but maybe not…

It was know to me that DCT with key lengths k1 and k2 can be expressed as SCT with key length k1k2. But such SCT is not equivalent to SCT with arbitrary key of length k1k2, since SCT produced from DCT has very very much reduced keyspace compared to general SCT.

Re: Challenge "Double Column Transposition Reloaded — Part 1"  

  By: Konubixe on Jan. 18, 2023, 9:46 p.m.

BTW: The two links at the end of page 4/4 produce an error 404 (not found)...

Re: Challenge "Double Column Transposition Reloaded — Part 1"  

  By: Theofanidis on Jan. 18, 2023, 11:28 p.m.

Dear Konubixe. Thanks for pointing this out. I checked the 2 links you mentioned. It seems the first one must be altered to, so actually replace the level-i into level-1. The second link seems to works for me, since the category level-x remains the same. Kind Regards, George Theofanidis

 Last edited by: Theofanidis on Jan. 19, 2023, 2:11 a.m., edited 2 times in total.

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