A Brief Early History of Cypher text

A Brief History of Early Cypher text

Scytale

One of the earliest forms of Cryptography is the scytale. (sounds like “Italy” in pronunciation).

The earliest known reference to this type of coded message dates back to the 7th Century B.C. Though it was mentioned that early, the references did not make clear on just how this method of cryptography worked. That is until Plutarch (a Greek historian, biographer, essayist who lived approx 46-120 A.D.) explained the method in his books “Parallel Lives”, in particular Volume 19 which talked about the Spartan General Lysander and how he communicated with his army.

Plutarch goes into detail on just how this method works..As shown in this quote from the aforementioned volume,

“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.

The idea behind this method of encryption was transposition. Not too dissimilar to the method used for the Caesar cipher explained later. Unlike the Caesar cipher though, the transposition in this case was achieved by using a rod (staff, baton) of a fixed width.

References:

http://en.wikipedia.org/wiki/Scytale

http://en.wikipedia.org/wiki/Plutarch#Parallel_Lives

http://en.wikipedia.org/wiki/LysanderScytale

Caesar Wheel

Another early form of ciphering was the Caesar wheel, also known as the Caesar Cipher.. Named after Julius Caesar (100 B.C. – 44 B.C.) who was documented as having used it.

This was essentially two disks of difference sizes. The smaller one on top of the larger one, joined in the center in such a . Each wheel would then be sectioned along its edge. Each of these sections had a letter of the alphabet. The key is set in advance such that both the sender and receiver what it is. The key was nothing more than a number which indicated the letter shift needed to encode or decode a message.

For example..

“If he had anything confidential to say, he wrote it in cipher, that is, by so changing the order of the letters of the alphabet,that not a word could be made out. “If anyone wishes to decipher these, and get at their meaning, he must substitute the fourth letter of the alphabet, namely D, for A, and so with the others.”

—Suetonius, Life of Julius Caesar

Caesar relied on a few things for this cipher to work, in particular the general illiteracy and the ignorance of the common man. What this means is that the average person couldn’t read and those who could would assume the coded message was another language. Now, consider this same cipher can be seen today on your average box of cereal which has activities on the back of the box, you have an idea of just how illiterate the average person was in Caesar’s time. It’s so easy to break, even a caveman—oops, a child can break it.

All Caesar did was off-set the alphabet by 4 spots. Even without knowing the off-set there are two ways by which to break this code. One is by letter frequency. Knowing which letters are used the most in the dominate language of the cipher. For instance, in English the top five most common letters used are “e”, ”t”, “a”, “o”, and “i”. The second is by brute force. Assuming for a moment that Caesar’s wheel had only 26 spots (one for each letter and no numbers) there would be 25 possibilities.

As recently as 1915 the Russian Army was using a variation of this cipher, mainly because the more common complicated ciphers were too difficult for their troops to decode.

References:

http://en.wikipedia.org/wiki/Caesar_cipher

http://en.wikipedia.org/wiki/Letter_frequency

http://www.scholastic.com/spyx/pdfs/Cipher_Wheel.pdf

Jefferson Disk

The Caesar Cipher would be the inspiration for Thomas Jefferson many centuries later. In 1795, Jefferson developed a cipher system with used a series of 36 wheels (or disks) positioned along a central spinal. Each wheel had on it’s edge a series of letters. Each disk is numbered and can be removed from the spinal, then put back on in any order. The order of the disks is the key.

How this works is this… Both the sender and the receiver must have the disks in the same order. For example, for a 10 disk version might have a key like this 2,4,6,8,10,1,3,5,7,9. From there, the sender would arrange the wheels to spell out the message they wanted along one row. Then finding another row, copy the message from another row and that would be the coded message that would be sent. Since the receiver would have the disks in the same order, all they’d have to do would be spell out the coded message on the individual wheels then rotate them all at once until the sender’s message was shown.

Though Jefferson invented the encryption, it didn’t catch on until later when it was also independently invented by Étienne Bazeries (French Cryptanalyst) about a century later. The Bazieries Cylinder was an improvement on the Jefferson Disk. With even further improvements, this would become the basis for the encoding system (M-94) the U.S. Army used from 1932- 1942.

References:

http://en.wikipedia.org/wiki/Jefferson_disk

http://en.wikipedia.org/wiki/Bazeries_Cylinder

http://www.monticello.org:8081/wheelcipher/wheelcipher.html