Ancient Cryptography

In the previous chapter, we discussed the introduction part of cryptography and we understand the eras of cryptography. Today we are going to learn about the ancient cryptography era.

Greece

The “Scytale” is the first cryptographic method that we can find when we analyze history. It was used in Greece in about 500 B.C which was developed by Spartans to send and receive secret messages. It is a device like a cylinder. And a strip of parchment uses to write messages on it as wounds in parchment. Once we remove the parchment it becomes an unclear message which is difficult to understand. So, to receive the exact message we should have the same size cylinder. It is a method that is considered as a type of transposition cipher. The problem with this method is there should be the same size cylinder. 

                                      Figure 1 - Scytale

Rome

But we consider Caesar cipher as the well-organized oldest cryptographic method which has been used in Rome by the empire Julius Caesar. It exploited English alphabetic letters and these letters applied to the plain-text according to the key which was selected by Caesar and generals. This key defined the shifting times of the English letters. He used it to send messages to the generals in the war field and it sent through a person. As a result of this cryptographic method which was used by the empire Julius Caesar, only generals could read the encrypted messages. Because the key and the key’s shifting time only were known by the generals and Caesar. This is a substitution type of cipher method. There were only 26 numbers of alphabetic letters and it directly matters to the key length and when we repeat the key, it will make it easy to identify the key and get our secret message. Then it takes only a few hours to break these secret keys and grab the hidden information. 

E.x:

Plain-text: ABCD

Key – 3

Ciphertext: DEFG

                                                   Figure 2 - Ceasar cipher

Alberti cipher disk

During the mid of the 15^th century, a man called Leon Battista Alberti invented a cryptographic method by developing a cipher disk. And this was the origin of the polyalphabetic cipher. So, he made the future of cryptography and the writer David khan considered Alberti as the “father of western cryptography” in his book “The codebreakers”. It was a substitution kind of method. There were two disks and one of them can rotate respective to the other disk, then we can easily slide and convert plain-text into cipher-text. The problem of this method was there should be a cipher disk for both sender and receiver, but other than it was a great method that arose a new chapter in cryptographic methods.

                                               Figure 3 - Alberti cipher disk

Steganography

Throughout the history, people used steganography to show secret warnings and messages to others, it always appeared as statues, pictures, and signs. But only certain people could be able to grab the message, it implied because only a group of people knew the meaning of these statues, pictures, and signs and other people did not see any other specialty of these. So it was always among the group of people, only through a member another person can get to know what it says and implies. It was one of the best cryptographic methods because it never implies that there was a hidden message and people never try to find the meaning of these things. This method was used by tribal societies in ancient times. But the ability to grab the secret message from the member of the group who knew the meaning of these signs.  

                                                                      Figure 4- Steganography

Vigenere cipher

Then in the 16^th century, Blaise de vigenere created vigenere cipher by improving Alberti’s polyalphabetic cipher. It was also a type of substitution cipher method. It had an asymmetric table that had English alphabetic letters. It looks like Caesar cipher because here also have shifting letters but here used an encryption key throughout the encryption and repeatedly used it with the plain-text. To make a secret message, first, we should find plain-text's first letter in the x-axis and encryption key's first letter in the y-axis, then we took the crossing letter according to the x and y-axis as the first letter of the cipher-text. Likewise letter by letter we can write the cipher-text. When the encryption key is shorter than the plain-text, then we can repeat the key until we cover the letters in the plain-text. 

Ex:

   Plain-text:   ATTACKATDAWN

  Keyword:    LEMONLEMONLE

  Cipher-text: LXFOPVEFRNHR

                                             Figure 5 -  Vigenere cipher

Jefferson cipher

In the 18^th century Thomas Jefferson invented a cipher system by developing the concept of Alberti’s and Vigenere’s which is known as “Jefferson disk” and also “Bazeries cylinder”. This a cryptographic method that can be taken under the substitution category. It had wheels and each of these wheels’ edges had 26 letters of the English alphabet. These wheels were numbered and each of these wheels was arranged in different alphabetic order. The order of these wheels was the cipher key, so both the sender and receiver should set these wheels according to the predefined order. Otherwise, the receiver couldn't grab the secret message. There was a unique technique related to this method, so the user and receiver should have a piece of proper knowledge about it. Although Jefferson invented it in 1795, it didn’t become famous but when Etienne Bazeries independently invented it after a century it became well-known and United States Army used it from 1923 to 1942. This method was good enough at that time, but now it is not capable of securing messages, because nowadays the computer power is very high and it takes a few hours to break it. And after a few years some problems arose regarding this method.

                                                   Figure 6 - Jefferson cipher

Here we conclude this chapter for ancient cryptography and in the next chapter, we will talk about world war cryptography.

All the credits for these photos go to their original owners.

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