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Rank Classical Ciphers By Security
Topic Started: Feb 6 2014, 01:02 AM (721 Views)
JoeJoeSchmidt
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I wanted to see how classical ciphers ranked, particularly some the early 20th century ciphers such as Trifid versus ADFGVX. I'd say no rotor machines and before 1960

Guessing, I would say, for example

0. Vernam Cipher (Goes Without Saying)
1. VIC Cipher
2. Trifid
3. ADFGVX
4. Playfair
5. Vigenere- Autokey
6. Vigenere- Repeating Keyword
7. Nomenclature
8. Nihilist
9. Homophonic Substitution
10. Mono-Alphabetic Substitution

Others no clue: Four Square, Bifid, Basic Double Transposition, etc.
Edited by JoeJoeSchmidt, Feb 6 2014, 01:02 AM.
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mok-kong shen
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My poor knowledge doesn't permit me to perform such a ranking at all. I like however to mention that that might very likely to a substantial degree depend on how certain parameters are set (intelligent vs. the opposite), the sizes, the key lengths, the key management and how error-prone the field operations are (which also depend on the training of the operators), etc. etc. I am afraid it could eventually in the end (with perhaps a couple of exceptions in the list) amount to ranking e.g. automobiles of approximately the same price class.
Edited by mok-kong shen, Feb 6 2014, 02:58 AM.
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JoeJoeSchmidt
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@mok

based on books and articles I have read, it is hard to differentiate between similar ciphers of specific eras sometimes, but generally there was a leap every once and a while. For a long time mono-alphabetic substitution reigned... it was improved with homophonic substitution and then complex arrangements called nomenclature through to the 19th century.... when adopted the vigenere was considered unbreakable until someone figured out you could break it down into parts..... then the fractionation/transposition combos in the 1900s that could be broken with a lot of effort until more general solutions were found in the 1930s. The last one I mentioned, VIC, was an attempt to just confuse cryptoanalysis with a wide variety of little tricks that added up to a very complex scheme. The Vernam Cipher or One Time Pad is just a vigenere cipher of course but it was discovered in the 1900s that it was unbreakable under certain conditions. It was haphazardly used by agents and such afterwards, but Rotor Machines became the seeming answer until the advent of computers.

Besides those leaps, or between the leaps, there is a lot of questions about what each era's ciphers were best. Plus there was a lot of little ciphers used by people that were improvements on the well-known ones.

edit: and yes I agree with your comment. But usually there is an opinion that a group of ciphers are inferior or superior to another... I.E. you read on wikipedia that four-square is superior to playfair "on the whole", you read on some site that the Jefferson Cipher is easy to break, yet other sites say it is superior in an important way to the Enigma (I know these are rotors), some say ADFGVX is a foolish cipher to have used, it was transposed only once and used a mono-alphabetic substituting polybius square... etc.
Edited by JoeJoeSchmidt, Feb 6 2014, 03:58 AM.
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mok-kong shen
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@JoeJoeSchmidt: I suppose most classical schemes should be evaluated nowadays also under the condition that the opponent has huge computer resources at his disposal and each single one would thus intuitively be rather weak. My humble personal view is that, instead of spending too much time to determine (noting that that could hardly be done entirely objectively) which one is the best and then choose to use it, it seems to be practically more advantageous and reasonable to consider good super-encipherments, i.e. appropriate combinations of a few different algorithms (and eventually with multiple rounds), taking due care of obtaining a nice mixture of diffusion and confusion (Shannon's terms). A dynamically variable session key (or its equivalent) of sufficient entropy is IMHO absolutely necessary. If certain steganographical aids are conveniently available, their utility could also be taken into consideration. (As an aside, concerning OTP, the history of Venona shouldn't be forgotten.)
Edited by mok-kong shen, Feb 6 2014, 10:58 AM.
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jdege
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Autokey vigs aren't very secure. Nomenclatures can be very secure.
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.
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novice
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Quagmire 4 cipher is difficult because it has three keys. That puts it up towards the top of the list.

A double transposition with long keys is really difficult. Recently a double transposition was ranked as nr 5 out of the top 25 most difficult unsolved ciphers.
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Grip2000
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2. "Doppelkastenschlussel" -Two-Box Cipher- by the Germans (with double encipherment feauture).

Page 35 ff -->
http://www.nsa.gov/public_info/_files/cryptologic_quarterly/world_war_II.pdf


It were the last of the "pencil-and-paper" systems used by a major army in a major conflict.
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jdege
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The super-special "unbreakable" cipher I invented when I was ten must rank close to the top ;)
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.
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JOE.TEKK1
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Where would you put poly-alphabetic ciphers with 6-10 alphabets? 9?

Mixed-Alphabet Vigenere ciphers were used before 1960, I believe.

Joe
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WTShaw
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I tend to accept the idea that strength might generally be indicated by amount of Ct required/suggested for solution. The ACA has such values suggested for a standard list of different popular ciphers.
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osric
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There is a more interesting and relevant set of statistics published 2-monthly by the ACA and that is the number of people who solved each cryptogram in the last issue. Looking at the list for July-August2013:

--there were the least number of solvers for Digrafid, TwoSquare and 6x6Bifid (29 to 34);

--there were the most for Chequerboard and Ragbaby (79 to 82).

If I were to make a few generalisation they would be

(1) the more keys used to encipher the cryptogram, the fewer solvers there tend to be -- although as ever there are exceptions.

(2) even within the same type of cryptogram there is a range of difficulties. For example the number of solvers for the 25 Aristocrats ranges from 71 to 115 in the issue mentioned.

(3) the longer the ciphertext the easier to solve, as we all know.

The old maxim that patience and application are well rewarded is, I have found, only too true. In the last issue it took me 6 weeks of off-and-on effort to solve the (to me) hardest cryptogram,. But then I finished up solving the whole bunch of 113 of them.
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