Maths
Language
Cryptography
Author
Christine Milleret; Charles Baudelaire
Target Group
17-18 years old
Brief Description
The earliest form of cryptography was the simple writing of a message, as most people could not read. In fact, the very word cryptography comes from the Greek words kryptos and graphein, which mean hidden and writing, respectively.

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A Brief History of Cryptography

By Tony M. Damico (2009).

The earliest form of cryptography was the simple writing of a message, as most people could not read.

In fact, the very word cryptography comes from the Greek words kryptos and graphein, which mean hidden and writing, respectively.

Early cryptography was solely concerned with converting messages into unreadable groups of figures to protect the message’s content during the time the message was being carried from one place to another.

In the modern era, cryptography has grown from basic message confidentiality to include some phases of message integrity checking, sender/receiver identity authentication, and digital signatures…

As early as 1900 B.C., Egyptian scribes used hieroglyphs in a non-standard fashion, presumably to hide the meaning from those who did not know the meaning.

The Greek’s idea was to wrap a tape around a stick, and then write the message on the wound tape. When the tape was unwound, the writing would be meaningless. The receiver of the message would of course have a stick of the same diameter and use it to decipher the message.

The Roman method of cryptography was known as the Caesar Shift Cipher. It utilized the idea of shifting letters by an agreed upon number (three was a common historical choice), and thus writing the message using the letter-shift. The receiving group would then shift the letters back by the same number and decipher the message. The Caesar Shift Cipher is an example of a Monoalphabetic Cipher.

It is easy to see why this method of encryption is simple to break. All a person has to do is to go down the alphabet, juxtapositioning the start of the alphabet to each succeeding letter. At each iteration, the message is decrypted to see if it makes sense. When it does appear as a readable message, the code has been broken. Another way to break Monoalphabetic ciphers is by the use of what is known as frequency analysis, attributed to the Arabs circa 1000 C.E. This method utilizes the idea that certain letters, in English the letter "e," for instance, are repeated more often than others. Armed with this knowledge, a person could go over a message and look for the repeated use or frequency of use, of a particular letter and try to substitute known frequently used letters.

As for the Greek method of using a stick, once the method was known, it was a simple matter of trying out sticks of different diameters until the message became readable.

The art and science of cryptography showed no major changes or advancements until the Middle Ages.

By that time, all of the western European governments were utilizing cryptography in one form or another. Keeping in touch with ambassadors was the major use of cryptography.

Leon Battista Alberti was known as “The Father of Western Cryptology,” most notably due to his development of polyalphabetic substitution. His method was to use two copper disks that fit together. Each one of them had the alphabet inscribed on it. After every few words, the disks were rotated to change the encryption logic, thereby limiting the use of frequency analysis to crack the cipher.

Polyalphabetic substitution went through a variety of changes and is most notably attributed to Vigenere.

Gilbert Vernam worked to improve the cipher, creating the Vernam-Vigenere cipher in 1918, but was unable to create one of significantly greater strength. His work did lead to the one time pad, which uses a key word only once, and it proved to be near unbreakable.

Additionally, it is important to mention the recently popularized "windtalkers." The Navajo’s used their own language as a basis for cryptography. The code was never broken and was instrumental in the victory in the Pacific Theatre during WWII.

In modern times, the public key method of cryptography has seen wide adoption. The use of a common public key and a private key held only by the sender is in use today as a form of asymmetric encryption; one of the uses of this method is for the sender to use the private key to encrypt the message and then anyone who receives the message uses the public key to decipher it. In this way, the receiver knows who the message had to come from. This method makes up the backbone of the Digital Signature.

Problems arise when communications between multiple organizations require the use of many public keys and knowing when to use which one. No matter which method is used, a combination of methods applied one after the other will give the best result.

In conclusion, no doubt cryptography and in a greater sense cryptology has played an enormous role in the shaping and development of many societies and cultures.

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Now see the files attached to find more documents and some exercises about Cryptography.

## Related files

 1.A brief history of Cryptography correction 81 KB A Visual History of Cryptography and Encryption Correction 1 MB A Visual History of Cryptography and Encryption Pictures 1 MB A Visual History of Cryptography and Encryption Texts 64 KB Caesar Cipher 684 KB Caesar Cipher Text 46 KB Murder in the Mathematics Faculty 173 KB Murder in the Mathematics Faculty Correction 58 KB The Vigenére Cipher 710 KB The Vigenére Cipher Text 60 KB
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