For other uses, see Scytale (disambiguation)

Scytale (disambiguation)

Scytale may refer to:* Scytale, an encryption tool used to perform a transposition cipher.* Scytale , a fictional character in the Dune universe created by Frank Herbert....

.

In cryptography

Cryptography

Cryptography is the practice and study of techniques for secure communication in the presence of third parties...

, a scytale (ˈskɪtəliː, rhymes approximately with Italy; also transliterated skytale, Greek σκυτάλη "baton") is a tool

Tool

A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...

 used to perform a transposition cipher

Transposition cipher

In cryptography, a transposition cipher is a method of encryption by which the positions held by units of plaintext are shifted according to a regular system, so that the ciphertext constitutes a permutation of the plaintext. That is, the order of the units is changed...

, consisting of a cylinder

Cylinder (geometry)

A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...

 with a strip of parchment wound around it on which is written a message. The ancient Greeks, and the Sparta

Sparta

Sparta or Lacedaemon, was a prominent city-state in ancient Greece, situated on the banks of the River Eurotas in Laconia, in south-eastern Peloponnese. It emerged as a political entity around the 10th century BC, when the invading Dorians subjugated the local, non-Dorian population. From c...

ns in particular, are said to have used this cipher to communicate during military

Military

A military is an organization authorized by its greater society to use lethal force, usually including use of weapons, in defending its country by combating actual or perceived threats. The military may have additional functions of use to its greater society, such as advancing a political agenda e.g...

 campaigns.

The recipient uses a rod of the same diameter

Diameter

In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...

 on which he wraps the parchment to read the message. It has the advantage of being fast and not prone to mistakes—a necessary property when on the battlefield. It can, however, be easily broken

Cryptanalysis

Cryptanalysis is the study of methods for obtaining the meaning of encrypted information, without access to the secret information that is normally required to do so. Typically, this involves knowing how the system works and finding a secret key...

. Since the strip of parchment hints strongly at the method, the ciphertext

Ciphertext

In cryptography, ciphertext is the result of encryption performed on plaintext using an algorithm, called a cipher. Ciphertext is also known as encrypted or encoded information because it contains a form of the original plaintext that is unreadable by a human or computer without the proper cipher...

 would have to be transferred to something less suggestive, somewhat reducing the advantage noted.

Encrypting

Suppose the rod allows one to write four letters around in a circle and five letters down the side of it.
The plaintext

Plaintext

In cryptography, plaintext is information a sender wishes to transmit to a receiver. Cleartext is often used as a synonym. Before the computer era, plaintext most commonly meant message text in the language of the communicating parties....

 could be: "Help me I am under attack".

To encrypt, one simply writes across the leather:

_____________________________________________________________

       |   |   |   |   |   |  |

       | H | E | L | P | M |  |

     __| E | I | A | M | U |__|

    |  | N | D | E | R | A |

    |  | T | T | A | C | K |

    |  |   |   |   |   |   |

_____________________________________________________________

so the ciphertext becomes, "HENTEIDTLAEAPMRCMUAK" after unwinding.

Decrypting

To decrypt, all one must do is wrap the leather strip around the rod and read across.
The ciphertext is: "HENTEIDTLAEAPMRCMUAK"
Every fifth letter will appear on the same line, so the plaintext becomes
HELPM...return to the beginning once the end is reached
...EIAMUNDERATTACK
After inserting spaces, the plaintext is revealed: "Help me I am under attack".

History

From indirect evidence, the scytale was first mentioned by the Greek poet Archilochus

Archilochus

Archilochus, or, Archilochos While these have been the generally accepted dates since Felix Jacoby, "The Date of Archilochus," Classical Quarterly 35 97-109, some scholars disagree; Robin Lane Fox, for instance, in Travelling Heroes: Greeks and Their Myths in the Epic Age of Homer , p...

, who lived in the 7th century BC. Other Greek and Roman writers during the following centuries also mentioned it, but it was not until Apollonius of Rhodes

Apollonius of Rhodes

Apollonius Rhodius, also known as Apollonius of Rhodes , early 3rd century BCE – after 246 BCE, was a poet, and a librarian at the Library of Alexandria...

 (middle of the 3rd century BC) that a clear indication of its use as a cryptographic device appeared. A description of how it operated is not known from before Plutarch

Plutarch

Plutarch then named, on his becoming a Roman citizen, Lucius Mestrius Plutarchus , c. 46 – 120 AD, was a Greek historian, biographer, essayist, and Middle Platonist known primarily for his Parallel Lives and Moralia...

 (50-120 AD):

The dispatch-scroll is of the following character. When the ephors send out an admiral or a general, they make two round pieces of wood exactly alike in length and thickness, so that each corresponds to the other in its dimensions, and keep one themselves, while they give the other to their envoy. These pieces of wood they call scytalae. Whenever, then, they wish to send some secret and important message, they make a scroll of parchment long and narrow, like a leathern strap, and wind it round their scytale, leaving no vacant space thereon, but covering its surface all round with the parchment. After doing this, they write what they wish on the parchment, just as it lies wrapped about the scytale; and when they have written their message, they take the parchment off and send it, without the piece of wood, to the commander. He, when he has received it, cannot otherwise get any meaning out of it,--since the letters have no connection, but are disarranged,--unless he takes his own scytale and winds the strip of parchment about it, so that, when its spiral course is restored perfectly, and that which follows is joined to that which precedes, he reads around the staff, and so discovers the continuity of the message. And the parchment, like the staff, is called scytale, as the thing measured bears the name of the measure.
—Plutarch, Lives (Lysander 19), ed. Bernadotte Perrin.

Due to difficulties in reconciling the description of Plutarch with the earlier accounts, and circumstantial evidence such as the cryptographic weakness of the device, several authors have suggested that the scytale was used for conveying messages in plaintext

Plaintext

In cryptography, plaintext is information a sender wishes to transmit to a receiver. Cleartext is often used as a synonym. Before the computer era, plaintext most commonly meant message text in the language of the communicating parties....

and that Plutarch's description is mythological.