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Challenge "Extended Handycipher — Part 4"

Challenge "Extended Handycipher — Part 4"  

  By: admin on June 28, 2016, 8:02 p.m.

Extended Handycipher is an enhancement of Handycipher. Part 4 is the same as Part 1, but uses an improved version of the cipher. You are given three encryptions of the plaintext generated with the same key, and the first 229 characters of the plaintext.
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Re: Challenge "Extended Handycipher — Part 4"  

  By: curmudgeon on Aug. 6, 2016, 5:43 p.m.

The following text was added to the challenge description in order to eliminate an ambiguity:

Remark: The end of each sentence is determined by a letter pair ". " or "? " which
is not part of an ellipsis, an abbreviation, or a quotation attribution.

Re: Challenge "Extended Handycipher — Part 4"  

  By: curmudgeon on Nov. 21, 2016, 10:47 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 "Extended Handycipher — Part 4"  

  By: curmudgeon on Jan. 22, 2017, 5:36 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.


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