| Welcome to Crypto. We hope you enjoy your visit. You're currently viewing our forum as a guest. This means you are limited to certain areas of the board and there are some features you can't use. If you join our community, you'll be able to access member-only sections, and use many member-only features such as customizing your profile, sending personal messages, and voting in polls. Registration is simple, fast, and completely free. Join our community! If you're already a member please log in to your account to access all of our features: |
| Proposal of a modern Jefferson's cylinder | |
|---|---|
| Tweet Topic Started: Apr 21 2014, 10:14 AM (244 Views) | |
| mok-kong shen | Apr 21 2014, 10:14 AM Post #1 |
|
NSA worthy
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]()
|
Recently fiziwig has in two threads suggested to use Jefferson's cylinder to generate passwords, resulting however in designs of such big sizes that are evidently not "portable" IMHO. Let me describe a method of employing Jefferson's cylinder for general encryption of plaintexts (assumed to be exclusively in lower case) that could be practical, in case there are producers thinking that it can be profitable to manufacture them with modern techniques. Employing aluminium alloy or similar materials one could make very light disks of diameter 2.5 cm, each carrying 26 symbols in appox. 3mm squares. (I believe that even a smaller diameter could be acceptable by the users, if a tiny magnifying glass is supplied to help reading. It is favourable however that a sufficiently large number of disks can be inserted into the device.) Produce 3 types of disks. Type L and U are in lower and upper case, while type S contains the digits and 16 special symbols. For each type there are disks with different randomly ordered symbols and designated with numerals, e.g. U39. Type S has a distinguished special symbol, say the space, which is specially marked (or else the user could choose his own distinguished special symbol, if desired). Now the user first determines his secret sequence of types, e.g. LULLSUL......, meaning that with a lower-case plaintext he will obtain a ciphertext with symbols in LULLSUL...... (due to the S's the ciphertext will be longer than the plaintext). He then chooses his secret sequence of disks accordingly, say L15, U03, L06, ...... On encryption he turns the disks in the device such that the alphabetical characters are in a line according to the plaintext, with the S type of disks having their distinguished special symbols shown up. Now the ciphertext can be read out at a secretly chosen number of lines away from the plaintext line. Following an idea of fiziwig, one could lump the types L and U into one single type A, with each disk containing a random permutation of the alphabet but randomly in either lower or upper case. (It may be remarked that practically one could extend the number of the symbols on the disks a tiny little bit, say to 30, so that each type A disk has now 4 arbitrarily chosen special symbols and consequently everywhere in the ciphertext special symbols have a chance (though unequal) of occurring.) Edited by mok-kong shen, Apr 22 2014, 07:45 AM.
|
![]() |
|
| fiziwig | Apr 21 2014, 06:31 PM Post #2 |
|
Elite member
![]() ![]() ![]() ![]() ![]() ![]() ![]()
|
How about if each disk only had the digits 0 through 5. Then you could convert the plaintext to numbers using this table:
(Or maybe a scrambled table) Then you could dial in the number version of the plaintext and read out the ciphertext number, then turn that number back into text with the same or different table. |
![]() |
|
| mok-kong shen | Apr 21 2014, 08:04 PM Post #3 |
|
NSA worthy
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]()
|
Maybe I gravely misunderstood. But that way you give up the requirement/convenience of a direct read-out e.g. of the passwords neeed for your banking, don't you? (And, using a table, why not simply use the kind of Playfair that you also suggested earlier, thus not needing a cylinder in the first place?) |
![]() |
|
| fiziwig | Apr 22 2014, 04:25 AM Post #4 |
|
Elite member
![]() ![]() ![]() ![]() ![]() ![]() ![]()
|
Yes, you are right. I overlooked that.
|
![]() |
|
| mok-kong shen | Apr 26 2014, 01:15 PM Post #5 |
|
NSA worthy
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]()
|
I have a (somewhat OT) question: In any fixed constellation, the Jefferson's cylinder could be considered as a polyalphabetical substitution table (one can take the first disk as the plaintext alphabet -- a bit more convenient for the user would be having a normal alphabet on the fixed part of the device) and employed accordingly for substitution with a key. Disregarding the issue of convenience or not of actual processing, would this way of doing encryption be better or worse in security than the normal mode of operating the Jefferson's cylinder?
Edited by mok-kong shen, Apr 26 2014, 07:29 PM.
|
![]() |
|
| fiziwig | Apr 26 2014, 09:52 PM Post #6 |
|
Elite member
![]() ![]() ![]() ![]() ![]() ![]() ![]()
|
It seems to me that if the alphabets on each wheel are different, and random, then you could turn the wheels to spell out the plaintext "ABCDEFGHIJKL..." and then have 25 different alphabets to work with, just like a Vig table. I think it would be just about the same as a Vig, but I'm not sure how easy it would be to keep track of where you get your next ciphertext letter from. It might be kind of confusing. |
![]() |
|
| mok-kong shen | Apr 27 2014, 07:50 PM Post #7 |
|
NSA worthy
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]()
|
@fiziwig: Aren't the alphabets on the wheels of a Jefferson's cylinder different and random, i.e. different mixed alphabets? (I have never seen a real Jefferson's cylinder.) I think I have to explain what I meant more clearly/precisely. One turns the (selected) disks such that on one line -- termed the key line below -- one can read out a certain key sequence for setting up the device. (The actual "key" for encrpyption is a subset of the characters of this key sequence.) This is the fixed constellation of the device for further processing. Obviously, if one imagines that the surface of the cylinder were cut just above the key line and flattened out then one has a normal polyalphabetical substitution table with mixed alphabets. (The common line at the top of a substitution table is missing. The common alphabet at the left of the table is also missing. But, as I wrote, one could take the alphabet on the leftmost disk, though a permuted one, to be the plaintext alphabet to enter the plaintext (the substitution table has thereby effectively one column less). To ease the encryption processing, the cylinder could be equipped with a freely movable (turnable) scale such that one could better locate the ciphertext character (of a certain column, chosen by a particular "key" character on the key line) corrresponding to the plaintext character on the plaintext alphabet. Edited by mok-kong shen, Apr 27 2014, 07:56 PM.
|
![]() |
|
| 1 user reading this topic (1 Guest and 0 Anonymous) | |
| « Previous Topic · General · Next Topic » |





![]](http://z2.ifrm.com/static/1/pip_r.png)



7:27 PM Jul 11