[image of digits]

Collections in Cryptology - Disk & Strip Cipher Slides
Key mechanisms in computation...
French cipher disk in silver by Nicolas Bion (1652-1733).
Maker of mathematical instruments to King Louis XIV. Diameter is 4.5cm or 1.77in.


"Rotularum (1680)."

from P. Gasparis Schotti's
1680, figure 1, page 95.

The lettering and numbering are exactly the same
as on the silver disk by Nicolas Bion.

U.S. Army Signal Corps Cipher Disk - WW1

Made of heavy, varnished card stock by Julien P. Frieze, Belport Observatory, Baltimore, MD. According the the instructions on the back, this was made to be used with the "Standard Heliograph." A later Stromberg-Carlson Heliograph is pictured here (scroll 2/3 of the way down the page). Diameter 86mm.


Close-up of the brass medallion on the
back with the maker's enscription.

Bulgarian Cipher Disk - WW1

Cipher Disk from World War One in Cyrillic.
This turned up in Bulgaria but I don't know any more about it.
Hand made from brass and aluminum the 40 sector boundaries are hand engraved and the numbers and letters are stamped in. When the index "A" is set to "A" the sectors are in good register. However, in other positions the alignment is less clear. Diameter 100mm.

Joseph Grassi "Cryptocode" machine.

Although the inventor claimed that the advantage of his device was that it produced "pronouncable" cipher text, thus enabling the owner to send encrypted messages at the reduced telegraphic rate, that feature was also the cryptanalytic weakness of the method: The machine replaced vowels with vowels and consonants with consonants, repeating the vowel/consonant pattern from the clear text in the cipher text.

U.S. Army Signal Corps Cipher Device Type M-94

Alcoa hallmark and mold number "2" for one of five types of disks.

Unidentified hallmark and mold number "2" for one of five types of disks.
The two inner circles form the letters "CCo."
The next outer circle appears to be two "D"s, back-to-back.
The outermost circle simply frames the hallmark?

<<< At left: One device assembled and one disassembled.
Three major varieties are known:
The M-94 was introduced to the Army Signal Corps 1921.
CSP-488 was introduced to the Navy 1928.
CSP-493 was introduced to the Coast Guard in 1939.

Rubber molds of an M-94 made circa 1980. A complete device was never cast.
Three disks are shown cast in brass. Click image for an enlargement.

German Cryptanalytic (Blank) Slide Rules

Aristo 90197

Aristo 100103
British Slidex
Srips and code sheet.

British SYKO/S.D.2 Strip Cipher
Used by the Allies for air/ground messaging during WW2.

U.S. Navy CSP-845 Strip Cipher

more information

U.S. Army M-138-A Strip Cipher
Two devices side-by-side. Commonly called the "strip system," it was used by
the State Department from the late 1930s and early 1940s
and widely by the Navy in WW2.

Five-strip section cut from a complete device.

Strip cipher strips: blanks and normal frequency alpabets.

U.S. Cryptanalysis
Punch-card sorting or perhaps computer printouts of analyses of four-letter code groups.

Narrow pages contain a count of the frequency of appearance of each four-letter code group.

"Green 33" dated January 17, 1946
Signed by Lt. Hunter

"Green 33" dated January 17, 1946
"Spec Proj" Signed by Lt. Hunter

Full pages contain an alphabetized listing of the occurrence of each four-letter code group in the context of the two preceeding and two following four-letter code groups. The system is identical to KWIC (Key-Word-In-Context) "invented" by Hans Peter Luhn of IBM 12 years later in 1958. ( 1 2 3 4 ) Many of the four-letter code groups are decrypted in pencil in English although the original codebook may have been in any language.

Column to the far left is labelled "Row." Columns to the right of the code groups are labelled "Column" and "Message ID."

No date or other markings

Mexican La Clave (The Key)


Year 1, Number 1: Official Organ of the Mexican Cryptographers Club


Not quite what they seem:

The "cryptex" from The Da Vinci Code.
Essentially it is a combination lock which opens up like a hollow cylinder once the correct code is dialed in.
In the film it protects a secret map and contains a tamper-proof mechanism (a vial full of acid)
which will break and destroy the contents if the wrong combination (key) is dialed in.

An M-94 at the International Spy Museum?
I thought it looked strange when I visited the display, so I snuck this photo and looked a little closer...
The nut is real (but it's been put on backwards), and maybe the axle, hub and cursor are real too.
But the mixed alphabets are exactly the same on each disk. The letters are crooked and in the wrong font.
Yes, they confirmed it: it's a replica...