Roots and Origins
The Chinese entry into cryptography was quite late because the Chinese script was complex and many Chinese did not know to read and write. Liutao (translated as 'Six Strategies'), an ancient Chinese book on military and political strategies, documents two cipher systems: Yinfu and Yinshu. An indirect ancient Chinese contribution to modern cryptography is in the form of the Chinese Remainder Theorem, which is used in public-key cryptography, a popular encryption method used over the Internet. This theorem was found in a book titled, "Sun Tzu Suan Ching" (Master Sun's Mathematical Manual) authored by Sun Zi.
It is said that the ancient Chinese wrote messages on silk, crushed it into a tiny ball and made the 'post man' swallow it after covering it with wax! Who would have thought cryptography would be taken to such limits?!
5th century B.C: The Spartans of Greece used a cylindrical staff, called a Skytale, to pass secret messages around in the military. This could be perceived as the maiden attempt in military cryptography. A narrow sheet of papyrus was wound around the skytale spirally and the secret message was written on the wound papyrus along the length of the skytale. Once the papyrus was unwound from the staff, the letters on the papyrus would make no sense: the message was thus encrypted. This encrypted message was now sent through a messenger to the recipient, who would use a similar staff with the same diameter to decrypt the message by winding the papyrus on the staff.
200 B.C: The Polybius Square: Polybius, a Greek historian and scholar, invented the Polybius Square. This Square consisted of a grid filled with the Greek alphabets. The rows and columns of the grid were numbered and thus any alphabet could be referred to by its row & column numbers. To encrypt a message, each letter of the plain text was located in the grid and replaced by its corresponding row and column number. Thus this system essentially replaces letters with numbers, a first of its kind recorded in history. The efficacy of this system lies in the fact that these numbers could now be transmitted in various ways: using a drum, using smoke, using flash-lights, tapping the bars in prison cells, etc.
The Polybius Square in English could look like this:
1 2 3 4 5
1 a b c d e
2 f g h ij k
3 l m n o p
4 q r s t u
5 v w x y z
First century B.C.: Julius Caesar introduced a simple encryption technique in which he replaced each letter in the plain text uniformly with a letter three positions down the alphabet. Thus 'A' would become 'D', 'Z' would become 'C' and so on. Caeser's use of this technique was recorded by Suetonius, a Roman historian during Caesar's period, in his work titled, "Vita Divi Juli" (The Life of Julius Caesar). This technique is now called Caesar's Shift or Caesar's Cipher. Though Julius Caesar used a transposition 'key' of three, later variations of the Caesar's Shift employed other keys as well. The strength of this cipher may have been adequate during Caesar's period - a time when literacy levels were very low. To a person who does not know to read and write, the plain text would make no more sense than the encoded message. Nevertheless, Caesar employed this method to protect his messages from prying eyes. However, given today's advances in cryptanalysis, deciphering a message encoded using the Caesar's Shift should be a walk in the park, even for the amateur cryptanalyst. A simple brute force attack would reveal the encoded message, as there are only twenty-five possible keys: probably a 10 nanosecond job for a computer. Even if the cipher system used to encode the message is not known, a frequency analysis on the cipher text would easily reveal whether the Caeser's shift was used.
The first signs of cryptography can be traced back to the 3" X 2" tablet containing the encrypted formula for preparation of pottery glaze, which was found on the banks of the river Tigris. The earlier inscriptions were made using cuneiform signs, where pictures were used to depict the objects, and with the advent of time, these inscriptions became so simple that they could even be used to convey abstract concepts.
Cryptography found its roots in ancient Babylonia, where it was used to conceal the procedures for making pottery glaze on a tablet. This hardened evidence that cryptography was not just a tool to provide personal security, but also business security.
Assyria followed an extra-ordinary concept called funerary cryptography where tombs had cuneiform symbols inscribed into them. This would provoke spectators to read the text out loud out of curiosity, thereby unintentionally vocalizing a prayer for the dead.
Cryptography is believed to have originated in Egypt. The first traces of cryptography can be dated to around 2000 B.C. when a scribe documented his master's biography using hieroglyphic substitution (replacing a known symbol by another) carved on stone. In Menet Khufu, a town on the banks of the river Nile, tablet inscription (using alternate hieroglyphs) and inscriptions on the tombs of deceased rulers were made, so as to make the text more important and inscrutable, as a political statement to publicize their religion, rather than for the purpose of hiding information as such.
1799 - A band of Napoleons soldiers uncovered the Rosetta stone near Rosetta (Egypt) which contains inscriptions about King Ptolemy V's tax policies and instructions to construct religious monuments. The passage was written in three languages: Demotic, Hieroglyphic and Greek and was translated by Jean-Francois Champollion in 1822. Comparative study of the three inscriptions helped shed some light in deciphering other hieroglyphic texts.
Middle East: Arabia
Abu Yusuf Ya'qub ibn Is-haq ibn as-Sabbah ibn 'omran ibn Ismail al-Kindi (801 - 873 AD), a Muslim Arab scientist devised a revolutionary technique in the field of cryptanalysis: frequency analysis. This method was found to be very effective in the case of mono substitution ciphers wherein each letter in the given language's alphabet is mapped to another letter, randomly. This mapping is then applied to the plain text to obtain the encoded text. If this message is decoded, a large number of plausible solutions are obtained. To make things easier, al-Kindi, in his book, "Risalah fi Istikhraj al-Mu'amma" (A Manuscript on Deciphering Cryptographic Messages) observed that in a given language there are certain letters which appear frequently and certain which do not. For example, in the English language, the letter 'E' appears most frequently, whereas 'Q' and 'Z' appear rarely. al-Kindi pointed out that by comparing the frequency of a letter in the cipher text with the frequencies of all the letters in the given language, the corresponding letter in the plain text could be guessed with little or no difficulty. As simple as it may seem, frequency analysis was a break-through in cryptanalysis.
The old Vikings of Scandinavia employed a cipher system similar to a Polybius Square along with the Caesar's Shift. For this purpose, the Rune alphabet was divided into three sections and two of these had five letters each and the other one had six letters. A letter in the plain text was located in the table and the corresponding section number was engraved along with the number of the preceding letter. Evidence of the use of cryptography by Vikings is 'written on stone' on the runestone of Rok in Ostergotland, Sweden.
Cryptic codes were used in India as a mode of secretive communication between spies all across the nation. The ciphers were based on alphabetic substitutions generally revolving around phonetics, and these codes were either vocalized or conveyed through sign language. Around the 4th century, the Kama Sutra of Vatsayana mentioned cryptography as the 44th and 45th of the 64th arts, and was incorporated as a way of concealed communication between lovers.
Sumeria holds credit for the oldest known written language: The Sumerian Cuneiform. This is believed to have originated from Uruk, in which words were depicted by pictures. With the advent of time, these 'word-pictures' graduated into 'ideographs', where symbols were used to express ideas, and finally came 'phonograms', which took on expressing sounds as well as the meaning of a picture at one go. Due to the complexity involved with this style of writing, it took upto the 19th century AD to decipher it!
Atbash Cipher - The Hebrews developed their own cipher which involved 'reverse alphabet single substitution'. They essentially devised this cipher to hide the names of various people and places in the Hebrew Bible. An adaptation of polyalphabetic substitution, the ATBASH cipher involves associating the first letter with the last letter, the second with the second last etc in the Hebrew code. So that would mean representing 'A' by 'T', 'B' by 'Sh' and so on, incidentally which is what gives the cipher its name - ATBASH (ATBSh). If you applied this technique to the English language, 'A' would be replaced by 'Z', 'B' by 'Y' etc.
- Hieroglyphs - Image source (GNU License)
- Rosetta Stone - Image source (Public Domain image)
- Runes - Image courtesy of Torbjorn "Toby" Andersson(published with permission).
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