Gripenstierna’s Cipher Machine
Two people could operate the device while only one saw the plaintext.
Historical device; original lost, later reconstructed from documents. No modern security claim.
Why This Matters
A clerk has to copy a secret dispatch. Must the clerk be allowed to read it? Gripenstierna’s device made that an engineering question: two viewing slits exposed different text to the people on opposite sides.
This Swedish design predates Jefferson’s 1790s wheel proposal. That chronology does not establish a line of descent between them. Its distinctive contribution here is the division of work, as well as its mechanical substitutions.
How It Works
The documented design uses 57 disks mounted on an axle. Each disk can turn independently and carries two alphabets. The authorized operator sets a row of plaintext on one side; the assistant copies the corresponding ciphertext from the other. For decryption the assistant sets the ciphertext, and the authorized reader takes off the plaintext.
Encipher: set plaintext.
Decipher: read plaintext.
Encipher: copy ciphertext.
Decipher: set ciphertext.
Original museum schematic of the roles only. This is not a drawing of the lost machine or a reconstruction of its alphabets.
The arrangement keeps routine copying apart from access to the message. It does not prove that an assistant with unrestricted access to the mechanism could never recover plaintext.
What Survives
Boris Hagelin’s account describes an invoice dated 26 August 1786 and written material found in the Swedish National Archives by Sven Wäsström. Hagelin reports that the original machine was lost and that Crypto AG built a replica using the surviving description. A photograph of that replica documents the reconstruction, not the appearance of an authenticated surviving original.
Bauer describes disk permutations as key material. Even 57! possible orders do not establish 254-bit cryptographic security: a count of arrangements is not a bound on the best attack. This exhibit makes no claim of demonstrated operational use or of a documented historical break.
Sources and Reading
- Friedrich L. Bauer, Decrypted Secrets: Methods and Maxims of Cryptology, 4th ed. (Springer, 2007), §7.5.2, pp. 131–132; see also p. 51 for the separation of operating roles.
- Boris Hagelin, The Story of Hagelin Cryptos, “The Beginning,” printed pp. 5–7 (PDF pp. 11–13): invoice, disk arrangement, operating roles and reconstruction.
- Further study: Bengt Beckman, “An Early Cipher Device: Fredrik Gripenstierna’s Machine”, Cryptologia 26(2), 2002, pp. 113–123.