The principle is as follows:
Both communication parties hold the same m*n column matrix, in which a character set consisting of characters to be encrypted is kept. When encrypting, find the corresponding plaintext characters, and then record the line number and column number.
Repeat the above process until all plaintext characters are searched, so that you can get a sequence C consisting of line numbers and column numbers.
The receiver receives the digital sequence C, continuously takes out the line number and column number from the sequence, and then finds out the characters corresponding to the lines and columns in the m*n column matrix.
Obviously, because both parties have the same matrix, it can be guaranteed that the receiver can recover the plaintext from the ciphertext.
In this encryption method, the key is obviously that matrix.
For this kind of encryption, many readers must have seen it from some novels.
How to implement this password on the computer? I believe it goes without saying that everyone has figured out what to do.
Yes, in essence, it is to remap the character set on the computer.
This mapping table is the key.
After all, this encryption method is actually single table replacement encryption (this encryption method will be discussed later).
Single table permutation encryption can be deciphered by frequency statistics, so it is an unsafe encryption method.
Cryptography, as a means to protect information, has experienced three development periods.
It was first used in military and diplomatic fields, and gradually entered people's lives with the development of science and technology.
In the manual stage, people only need to encrypt characters through paper and pen.
Cryptography has a long history, and the use of passwords by human beings can be traced back to the Babylonian era.
The Festus disk shown in the figure below is a clay disk with a diameter of about 160mm, which began in17th century BC and has letters with obvious spaces between words on its surface.
In recent years, some researchers think that it records some kind of ancient astronomical calendar, but the truth is still a mystery.
With the rise of the industrial revolution, cryptography has also entered the machine age and the electronic age.
Compared with manual operation, the electronic cipher machine adopts more excellent and complex encryption means and has higher encryption and decryption efficiency.
The most representative is ENIGMA as shown in the following figure.
ENIGMA is an encrypted electronic device invented by Germany in 19 19. It has proved to be one of the most reliable encryption systems in history.
During World War II, it was widely used in railways and enterprises by the German army, which made the secret communication technology of the German army in a leading position.
Although the encryption equipment has made great progress during this period, the theory of cryptography has not changed much, and the main means of encryption are still substitution and transposition.
The emergence of computers makes it possible for passwords to perform highly complex operations.
Until 1976, in order to meet the requirements of computer network communication and business confidentiality, cryptography made a real breakthrough and entered the stage of modern cryptography.
Modern cryptography has changed the single encryption method of classical cryptography, and incorporated a lot of rich knowledge such as number theory, geometry and algebra, making cryptography develop more vigorously.
Today, countries all over the world still attach great importance to the study of cryptography, which has developed into the era of modern cryptography.
Cryptography has become a comprehensive science integrating physics, quantum mechanics, electronics, linguistics and other majors, and advanced theories such as "quantum cryptography" and "chaotic cryptography" have emerged, which play a very important role in information security.
The original password appeared in Sparta, Greece. A tape is wound around a wooden stick, and plain text is written along the longitudinal axis of the stick. There are only confused secret letters on the untied tape.
The decryptor only needs to find a wooden stick with the same diameter, and then wrap it with tape to read meaningful plaintext along the longitudinal axis of the wooden stick.
This is the earliest transposition cryptography.
In BC 1 century, the famous Caesar cipher was used in the Gaul War, which is a simple and easy one-letter substitution cipher.
In the 9th century, * * * cryptographer Alkindi (also known as ishak Ishaq, (80 1? ~873), an astronomer, philosopher, chemist and music theorist, put forward the frequency analysis method of decryption, and deciphered the password by analyzing and calculating the frequency of secret characters.
/kloc-in the middle of the 6th century, the Italian mathematician cardano (G. Cardano,1501-1576) invented the cardano grid, which covered the ciphertext and could read the plaintext from the grid. This is an early split code.
/kloc-In the late 6th century, Philips of England successfully cracked the coded letter of Mary, Queen of Scotland, which planned to assassinate Queen Elizabeth of England. This decryption sent Mary to the guillotine.
Almost at the same time, French diplomat Genard Blaise de Vigener (1523-1596) proposed the famous ViGenard square cipher and Vigenerecypher, which are alternative ciphers with multi-table encryption, and can invalidate the frequency analysis methods of Al-Kindy and Phillips.
In A.D. 1863, the Prussian major Kasinsky cracked the key words from the length for the first time.
Charles Babbage in Britain also deciphered the Genard code by carefully analyzing the structure of the cipher letters.
At the beginning of the 20th century, the First World War came to a critical moment. Room 40, a special organization for deciphering codes in Britain, deciphered the famous "Qi Telegraph" by using the seized German codebook, which prompted the United States to give up its neutrality and participate in the war, thus changing the course of the war.
At the end of World War II, exactly, 19 18, the American mathematician Gilbert Wynam invented the one-time note cipher. It is an absolutely indecipherable encryption system in theory and is known as the holy grail of cryptography.
However, the difficulty of generating and distributing a large number of random keys greatly limits its practical application. On the other hand, its security is more uncertain.
During World War II, mathematicians and scientists joined the decoding team, which was mainly composed of linguists and humanists, in the process of deciphering the famous "Enigma" cipher machine in Germany.
Alan mathison turing, the father of computer, joined the decoding team at this time and invented a better decoding method.
At the same time, this excellent team designed the first human computer to assist in the cracking work.
Obviously, the increasingly popular computer is also a military-to-civilian product.
Americans cracked the Japanese "97" password, named "Mizi".
Relying on the former, many of Germany's major military actions are not secrets to its allies; Relying on the latter, American forces killed Isoroku Yamamoto, commander-in-chief of the Japanese fleet who attacked Pearl Harbor.
Also in World War II, Navajo, an indigenous language, was used as a password by the US military, which can be seen from The Whisperwind directed by John Woo.
The so-called Whisperer refers to the Navajo signal soldier specially used by the United States during World War II.
On the Pacific battlefield between Japan and the United States in World War II, the US Navy Department asked the Wayo people in northern Mexico and Arizona to use Jowana for information transmission.
Navajo's grammar, intonation and vocabulary are extremely unique and unknown to the world. At that time, except Navajo, only 10 to 20 Americans could understand this language.
This is a successful combination of cryptography and linguistics, and the Navajo code has never been cracked in history.
1975 15 years 10 month 15, DES (Data Encryption Standard) for encrypting computer systems and networks was promulgated as a national standard by the American National Bureau of Standards, which was a landmark event in the history of cryptography.
1976, at that time, Diffie and Hellman of Stanford University in the United States put forward a new idea of public key cryptography (paper "New Direction of Cryptography"), which divided keys into encrypted public keys and decrypted private keys, which was a revolution in cryptography.
From 65438 to 0977, Ronald Rivest, adi shamir and Ryan Aderman in the United States put forward the first perfect public key cryptosystem-RSA system, which is an algorithm based on factorization of large numbers.
1985, David Deutsch, a physicist at Oxford University in England, put forward the preliminary idea of quantum computer. Once this computer is built, it can complete the factorization of large numbers in 30 seconds, which can only be completed in traditional computers 1000 billion years, thus cracking RSA's use of this large number to generate public key encrypted information.
In the same year, according to his agreement on quantum cryptography, Ben of the United States realized the communication of quantum cryptography encrypted information for the first time in the laboratory.
Although the communication distance is only 30 cm, it proves the practicability of quantum cryptography.