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Challenge "Handycipher — Part 3"

Challenge "Handycipher — Part 3"  

  By: admin on March 3, 2015, 11:40 p.m.

Handycipher is a newly designed cipher to permit pen-and-paper encrypting and decrypting, while providing a significantly high level of security. You got only the ciphertext of the 993-character plaintext.
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 Last edited by: admin on Oct. 31, 2021, 2:55 a.m., edited 1 time in total.

Re: Challenge "Handycipher — Part 3"  

  By: curmudgeon on Nov. 21, 2016, 10:53 a.m.

In order to remove a newly discovered weakness in the cipher, a slight change is required in the Handycipher encryption and decryption algorithms. In two weeks three new challenges, Handycipher Parts 7, 8. and 9, will be offered duplicating Parts 4, 5, and 6 with new plaintexts but using the strengthened cipher.

At that time Handycipher Parts 3 - 6 as well as Extended Handycipher Parts 4 - 6 will be reassigned from Level III to Level II, because the changes made to the algorithms will call attention to the weakness which significantly reduces the level of difficulty. Handycipher Part 9 will then be the sole Level III challenge in the series.

Re: Challenge  

  By: Greko on Nov. 26, 2016, 1:48 p.m.

Dear MTC3 team,

I have a simple question, and unfortunately I believe I know the answer. You mention in the above post that some Handycipher challenges will be underrated from level III to level II. I understand that this affects only three members of the contest, the only successful solvers of the "advanced" Handycipher challenges (Integral,michaelm and me). So I have to ask. We should expect our points to be adjusted according to this change?

Handycipher part-3 is a level III challenge for almost two years. It took me a whole summer to solve it. I had to develop cryptanalytic techniques that I had not ever imagined I could develop in order to break this cipher. And it was fun, more fun than any other challenge I have solved. So as I am in the top ten of the hall of fame I believe I have the right to say that it is a hard challenge, a level III challenge. I believe that it was not easier for the other two users as well (I would like to know their opinion).

The new change in the algorithm that exposes a weakness did not affect our work (because we do not know that change yet). So, in case you are thinking of reducing the points awarded for these challenges, do you believe it is fair for this three users?

This is a natural question for the level III challenges. The contest was open 5 years ago, is open now and I hope it will be open in ten years from now. But a challenge published now in 2016 as level III, maybe in ten years from now will be of level II difficulty due to new discoveries. A user that solves it now in 2016 should be awarded the points of a level III challenge because that is the actual difficulty at this time. After 5 years maybe a paper appears that reduces it to a simple programming challenge. That does not mean that the first one that solved it put the same amount of work as the one after five years.

I participate in this contest for more that 4 years and I believe it is a fair contest. I want to believe that. So I would like to suggest to the MTC3 team to think carefully how they are going to handle this change.

Best regards
Greko

Re: Challenge  

  By: be on Nov. 26, 2016, 6:59 p.m.

You mention in the above post that some Handycipher challenges will be underrated from level III to level II … We should expect our points to be adjusted according to this change?

Hello Greko,

thanks for your valid question and your well-explained arguments. We always take the thoughts of the experienced and longtime solvers very serious. And we appreciate the hard cryptanalytical work done to solve these challenges.

However, there is a misunderstanding, and we probably didn't make it clear enough in our post:

  • Yes, the mentioned existing L3 Handycipher challenges will be downgraded.
  • However, this does not effect the points already awarded for their solution.
  • When downgrading a challenge because hints are published this is effective just from the date of the downgrade or the date, the hints got public.
  • So even if someone solves such a challenge today he/she gets the points for a L3 challenge. But after the hints are becoming public (which is close to now because we know of an upcoming publication), he/she gets the points for a L2 challenge.

In summary:
Points awarded for solutions submitted prior to the reassignment would not be recalculated.

So I guess, everything is planned to be handled just in the way you wished them to be. If not, please let us know.

Best regards, be

Re: Challenge  

  By: Greko on Nov. 26, 2016, 7:46 p.m.

Hello Be,

Thank you for your answer. It was definitely not clear to me how you would handle the change. That is why I thought I should ask.

I am glad that you appreciate the work done in order to solve these challenges and your decision shows that.

Continue the good job.

Best regards
Greko

Re: Challenge "Handycipher — Part 3"  

  By: curmudgeon on Jan. 22, 2017, 5:31 a.m.

After further consideration of the extent to which the changes made to the algorithms will call attention to the weakness, it has been decided not to downgrade Handycipher Parts 3 - 6 and Extended Handycipher Parts 4 - 6 to Level II.

Handycipher Parts 7, 8. and 9, are now available as Level III challenges.

Re: Challenge "Handycipher — Part 3"  

  By: RobertThomas on March 1, 2021, 11:27 p.m.

After further consideration of the extent to which the changes made to the algorithms will call attention to the weakness, it has been decided not to downgrade Handycipher Parts 3 - 6 and Extended Handycipher Parts 4 - 6 to Level II.

Handycipher Parts 7, 8. and 9, are now available as Level III challenges.

thanks for your valid question and your well-explained arguments. We always take the thoughts of the experienced and longtime solvers very serious. And we appreciate the hard cryptanalytical work done to solve these challenges.


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