History of secret codes

« appear in the clear message with the same frequency as the coded message.

We study the frequency ofappearance of the letters of a coded message: A=9 %, D=3 %, E=15 %, I=8 %, Q=1 %, S=8 %, etc.

…Furthermore, we apply certain rules of the crossword fans: q followed of an u, c often followed by an h, s often atthe end of word...

The analysis in frequency was a basic tool of codebreaker.IV) The Renaissance in west and the British drama : Between 800 and 1300, it is the monasteries which were, in West; the places of encipher and deciphering.

Indeed,the monks were statistically the most educated for this period.

They knew Caesar cipher but used as well Greek,Hebrew, Arabic and symbols built by them as musical notes.

So, a melody became a secret code.The British drama : it takes place during the religious wars between Catholics and Protestants.

Marie Stuart wasduring a period Queen of Scotland before losing the throne for the benefit of his son.

But she was imprisoned by thequeen of England by a plot which badly turned.

A partisan catholic group of Marie Stuart intended to go up a coupd'état.

The weakness of Marie's code provoked her arrest and her bloody execution on February 8th, 1587. V) Vigenere cipher : break of Caesar cipher : Blaise de Vigenère, French diplomat, born in 1523, decided to attack Caesar cipher by attacking the distribution infrequency of letters.

We use for it a table.It consists on the alphabet written down twenty-six times in different rows.

Each alphabet is shifted cyclically tothe left compared to the previous one.

This corresponds to the twenty-six possible Caesar ciphers.

The letters ofthe plain text are read on the first row.

The alphabet used at each point depends on a repeated keyword.

Eachcorresponding letter of the repeated keyword is read in the first column.Blaise de Vigenère, French diplomat, born in 1523, decided to attack Caesar cipher by attacking the distribution infrequency of letters.

We use for it a table.VI) The code ADFGVX : Germans elaborate the code ADFGVX with the aim of the first world war.

It was finalized and spread on March 5th,1918 before the big offensive of March 21st.

The principle of the encoding was Vigenère's one, but it contained inmore ten decimal figures, what with the eyes of the specialists consolidated the indecipherability … This one isbroken on June 2nd, 1918 by the French Georges Painvin after a relentless work of 3 months (at nights and days). VII ) The Machine Enigma : Scherbius and Ritter invented a machine to calculate electric and automatic Enigma.

The invention considered atfirst curious was then recognized as having a redoubtable efficiency.

In spite of its very high price, severalcountries or big companies equipped themselves with it.

Germany came there late (1930) but used it during theSecond World War.

The principle of the machine leans on Caesar cipher.The deciphering of Enigma was very difficult.

Schmidt contributed to its progress by selling the plans of Enigma to aFrench secret agent of Rex's name.

The English people who want to find quickly the functioning of this machinegathered 7000 specialists of the figure in Bletchey Park.It is then that appeared in Bletchey Park, Alan Turing, Mathematician of Cambridge and first inventor of thecomputing algorithms.

The codebreaker changed the course of the war thanks to his "bombs", the first mechanicalmachines of the decoding. VII) RSA ( Rivest, Shamir, Adleman, 1977)This algorithm is based on the use of a pair of keys consisted of a public key to encipher and a key deprived todecipher confidential data.

The public key corresponds to a key which is accessible by any person wishing to codeinformation, the private key is as for it reserved for the person having created the pair of keys.

When two persons,or more, wish to exchange confidential data, a person (Alice) takes care of the creation of the pair of keys, sendsher public key to the other person (Bob) who can then code the confidential data by means of this one then sendthe data encoded to the person having created the pair of keys, Alice.

This last one can then decipher theconfidential data by means of her private key.This system requires "routes".

We can delete it: if Bob wants to send to Alice a secret message, Alice scrambles theconnection by a means known for her.

Bob sends his message to Alice.

It is blurred, but Alice acquaints with it "byuntangling" it, according to her process. Alice has two keys: a public one(green) and a private one (red).

She gives a public key to Bob and keeps herprivate key. Bob codes his message with the public key and sends it to Alice.

Alice can decode the code with her private key. VIII) Future : Today still, certain messages are illegible (as the disk of Phaistos, in Crete), because written in a language whichwe have no sufficient length of text, to reconstitute an alphabet.The cryptography has another beautiful future in front of it, and will not hesitate to use the most advancedtechnologies.

But today, we are almost sure being able to pass on a message without it is intercepted.. »