From time immemorial, ciphers have been used to keep secrets. One of the most ancient cipher systems, information about which history has brought to us, is wandering. It was used by the ancient Greeks as far back as the 5th century BC. In those days, Sparta, supported by Persia, waged a war against Athens. The Spartan general Lysander began to suspect the Persians of a double game. He urgently needed true information about their intentions. At the most critical moment, a messenger slave arrived from the Persian camp with an official letter. After reading the letter, Lysander demanded a belt from the messenger. It turns out that on this belt a loyal friend (now we would say "secret agent") Lysandra wrote an encrypted message. On the belt of the messenger, various letters were written in disarray, which did not add up to any words. Moreover, the letters were written not along the waist, but across. Lysander took a wooden cylinder of a certain diameter (wandering), wound the messenger's belt around it in such a way that the edges of the belt turns closed, and the message he was waiting for was lined up on the belt along the generatrix of the cylinder. It turned out that the Persians were plotting to strike the Spartans with a surprise stab in the back and killed Lysander's supporters. Having received this message, Lysander unexpectedly and secretly landed near the location of the Persian troops and with a sudden blow defeated them. This is one of the first known cases in history in which a cipher message played an extremely important role.
It was a permutation cipher, the cipher text of which consists of plaintext letters rearranged according to a certain, but not known to outsider law. The cipher system here is the permutation of letters, the actions are the winding of the belt around the wandering. The cipher key is the diameter of the wandering. It is clear that the sender and recipient of the message must have ropes of the same diameter. This corresponds to the rule that the encryption key must be known to both the sender and the recipient. Wandering is the simplest type of cipher. It is enough to pick up several wanderings of various diameters, and after winding the belt on one of them, the plain text would appear. This encryption system was decrypted in ancient times. The belt was wound on a conical wander with a slight taper. Where the cross-sectional diameter of the conical skitala is close to the diameter used for encryption, the message is partially read, after which the belt is wound around the skitala of the required diameter.
Julius Caesar widely used ciphers of a different type (replacement ciphers), who is even considered to be the inventor of one of these ciphers. The idea of the Caesar cipher was that on paper (papyrus or parchment) two alphabets of the language in which the message will be written are written one under the other. However, the second alphabet is written under the first with a certain (known only to the sender and recipient, shift). For the Caesar cipher, this shift is equal to three positions. Instead of the corresponding plaintext letter, which is taken from the first (upper) alphabet, the lower alphabet character under this letter is written into the message (ciphertext). Naturally, now such a cipher system can be easily broken even by a layman, but at that time the Caesar cipher was considered unbreakable.
A somewhat more complex cipher was invented by the ancient Greeks. They wrote out the alphabet in the form of a 5 x 5 table, denoted rows and columns with symbols (that is, they numbered them) and instead of a plaintext letter they wrote two symbols. If these characters are given in a message as a single block, then with short messages for one specific table, such a cipher is very stable, even according to modern concepts. This idea, which is about two thousand years old, was used in complex ciphers during the First World War.
The collapse of the Roman Empire was accompanied by the decline of cryptography. History has not preserved any significant information about the development and application of cryptography in the early and middle Middle Ages. And only a thousand years later, cryptography is reviving in Europe. The sixteenth century in Italy is a century of intrigue, conspiracy and turmoil. The Borgia and Medici clans vie for political and financial power. In such an atmosphere, ciphers and codes become vital.
In 1518, Abbot Trithemius, a Benedictine monk living in Germany, published a book in Latin called Polygraphy. It was the first book on the art of cryptography and was soon translated into French and German.
In 1556, the doctor and mathematician from Milan Girolamo Cardano published a work describing the encryption system he invented, which went down in history as the "Cardano Lattice". It is a piece of hard cardboard with holes cut in random order. The Cardano lattice was the first application of the permutation cipher.
It was considered an absolutely strong cipher even in the second half of the last century, with a sufficiently high level of development of mathematics. So, in the novel by Jules Verne "Mathias Sandor" dramatic events develop around a cipher letter sent with a dove, but accidentally fell into the hands of a political enemy. To read this letter, he went to the author of the letter as a servant in order to find a cipher grid in his house. In the novel, no one has the idea of trying to decrypt a letter without a key, based only on knowledge of the applied cipher system. By the way, the intercepted letter looked like a 6 x 6 letter table, which was a gross error of the encryptor. If the same letter had been written in a line without spaces and the total number of letters with the help of the supplement had not been 36, the decryptor would still have to check the hypotheses about the encryption system used.
You can count the number of encryption options provided by a 6 x 6 Cardano lattice. deciphering such a lattice for several tens of millions of years! Cardano's invention proved to be extremely tenacious. On its basis, during the Second World War, one of the most durable naval ciphers in Great Britain was created.
However, by now, methods have been developed that allow, under certain conditions, to decipher such a system quickly enough.
The disadvantage of this lattice is the need to reliably hide the lattice itself from strangers. Although in some cases it is possible to remember the location of the slots and the order of their numbering, experience shows that the memory of a person, especially when the system is rarely used, cannot be relied on. In the novel "Matthias Sandor", the transition of the lattice into the hands of the enemy had the most tragic consequences for the author of the letter and for the entire revolutionary organization of which he was a member. Therefore, in some cases, less strong, but simpler encryption systems that are easy to recover from memory may be preferable.
Two people could claim the title of "father of modern cryptography" with equal success. They are the Italian Giovanni Battista Porta and the Frenchman Blaise de Vigenère.
In 1565, Giovanni Porta, a mathematician from Naples, published a substitution cipher system that allowed any plaintext character to be replaced by a cipher letter in eleven different ways. For this, 11 cipher alphabets are taken, each of them is identified by a pair of letters that determine which alphabet should be used to replace the plaintext letter with a cipher alphabet. When using Ports cipher alphabets, in addition to having 11 alphabets, you also need to have a keyword that defines the corresponding cipher alphabet at each encryption step.
Giovanni Porta's table
Usually the ciphertext in the message is written in one piece. On technical communication lines, it is usually transmitted in the form of five-digit groups, separated from each other by a space, ten groups per line.
The Ports system has a very high durability, especially with arbitrary choice and writing of alphabets, even according to modern criteria. But it also has disadvantages: both correspondents must have rather cumbersome tables that must be kept from prying eyes. In addition, you need to somehow agree on a keyword, which must also be secret.
These problems were solved by diplomat Vigenère. In Rome, he became acquainted with the works of Trithemius and Cardano, and in 1585 he published his work "A Treatise on Ciphers." Like the Ports method, the Vigenère method is table-based. The main advantage of the Vigenere method is its simplicity. Like the Ports system, the Vigenere system requires a keyword (or phrase) for encryption, the letters of which determine which of the 26 cipher alphabets each specific letter of the plaintext will be encrypted by. The key text letter defines the column, i.e. specific cipher alphabet. The letter of the ciphertext itself is inside the table corresponding to the letter of the plaintext. The Vigenere system uses only 26 cipherfats and is inferior in strength to the Ports system. But the Vigenere table is easy to restore from memory before encryption, and then destroy. The stability of the system can be increased by agreeing not on a key word, but on a long key phrase, then the period of use of cipher alphabets will be much more difficult to determine.
Vigenère cipher
All encryption systems prior to the twentieth century were manual. With a low intensity of cipher exchange, this was not a disadvantage. Everything changed with the advent of the telegraph and radio. With the increase in the intensity of the exchange of cipher messages by technical means of communication, the access of unauthorized persons to the transmitted messages has become much easier. Requirements for the complexity of ciphers, the speed of encryption (decryption) of information have increased dramatically. It became necessary to mechanize this work.
After the First World War, the rapid development of the encryption business began. New cipher systems are being developed, machines are invented that speed up the encryption (decryption) process. The most famous was the mechanical cipher machine "Hagelin". The company for the production of these machines was founded by the Swede Boris Hagelin and still exists today. The Hagelin was compact, easy to use, and provided high strength of the cipher. This cipher machine implemented the replacement principle, and the number of cipher alphabets used exceeded that of the Ports system, and the transition from one cipher alphabet to another was carried out in a pseudo-random manner.
Car Hagellin C-48
Technologically, the operation of the machine used the principles of operation of adding machines and mechanical automatic machines. Later, this machine underwent improvements, both mathematically and mechanically. This significantly increased the system's durability and usability. The system turned out to be so successful that during the transition to computer technology, the principles laid down in Hagelin were electronically modeled.
Another option for the implementation of the replacement cipher was disk machines, which from their very inception were electromechanical. The principal encryption device in the car was a set of disks (from 3 to 6 pieces) mounted on one axis, but not rigidly, and in such a way that the disks could rotate around the axis independently of one another. The disc had two bases, made of bakelite, into which the contact terminals were pressed according to the number of letters of the alphabet. In this case, the contacts of one base were electrically connected internally with the contacts of the other base in pairs in an arbitrary manner. The output contacts of each disk, except for the last one, are connected through fixed contact plates to the input contacts of the next disk. In addition, each disk has a flange with protrusions and depressions that collectively determine the character of the step motion of each disk at each encryption cycle. At each clock cycle, encryption is carried out by impulse voltage supply through the input contact of the switching system corresponding to the plaintext letter. At the output of the switching system, the voltage appears on the contact, which corresponds to the current letter of the ciphertext. After one cycle of encryption has been completed, the disks are rotated independently of one another by one or several steps (in this case, some disks may be idle at all at each step). The law of motion is determined by the configuration of the disc flanges and can be considered pseudo-random. These machines were widespread and the ideas behind them were also electronically modeled during the advent of the electronic computing era. The security of the ciphers produced by such machines was also exceptionally high.
During World War II, the Enigma disk machine was used to encrypt Hitler's correspondence with Rommel. One of the vehicles fell into the hands of British intelligence for a short time. Having made an exact copy of it, the British were able to decrypt secret correspondence.
The following question is pertinent: is it possible to create an absolutely strong cipher, i.e. one that would be unrevealed even theoretically. The father of cybernetics, Norbert Wiener, argued: “Any sufficiently long piece of ciphertext can always be decrypted, provided that the opponent has enough time for this … Any cipher can be decrypted if only there is an urgent need for it and the information that is supposed to be obtained is worth the cost. means of effort and time . If we are talking about a cipher generated in accordance with any precisely and unambiguously defined algorithm, no matter how complex it may be, then this is indeed the case.
However, the American mathematician and information processing specialist Claude Shannon showed that an absolutely strong cipher can be created. At the same time, there is no practical difference between an absolutely strong cipher and the so-called practical strength ciphers (implemented using specially developed complex algorithms). An absolutely strong cipher must be generated and used as follows:
- the cipher is generated not using any algorithm, but in a completely random way (throwing a coin, opening a card at random from a well-mixed deck, generating a sequence of random numbers by a random number generator on a noise diode, etc.);
- the length of the ciphertext should not exceed the length of the generated cipher, i.e. one cipher character shall be used to encrypt one character of the plaintext.
Naturally, in this case all the conditions for the correct handling of ciphers must be fulfilled and, above all, the text cannot be re-encrypted with a cipher that has already been used once.
Absolutely strong ciphers are used in cases where the absolute impossibility of decryption by the enemy of the correspondence must be guaranteed. In particular, such ciphers are used by illegal agents operating on enemy territory and using cipher notes. The notebook consists of pages with columns of numbers, chosen entirely at random, called a block cipher.
The encryption methods are different, but one of the simplest is the following. The letters of the alphabet are numbered with two-digit numbers A - 01, B - 02 … Z - 32. Then the message "Ready to meet" looks like this:
plain text - READY TO MEET;
open digital text - 0415191503 11 03181917062406;
block cipher - 1123583145 94 37074189752975;
ciphertext - 1538674646 05 30155096714371.
In this case, the ciphertext is obtained by the numerical addition of the plain digital text and the block cipher modulo 10 (i.e., the transfer unit, if any, is not taken into account). The ciphertext intended for transmission by technical means of communication has the form of five-digit groups, in this case it should look like: 15386 74648 05301 5509671437 16389 (the last 4 digits are added arbitrarily and are not taken into account). Naturally, it is necessary to notify the recipient which page of the cipher note is used. This is done in a predetermined place in plain text (in numbers). After encryption, the used cipherpad page is torn out and destroyed. When decrypting the received cryptogram from the ciphertext, you need to subtract the same cipher modulo 10. Naturally, such a notebook must be kept very well and secretly, since the very fact of its presence, if it becomes known to the enemy, means the agent's failure.
The arrival of electronic computing devices, especially personal computers, marked a new era in the development of cryptography. Among the many advantages of computer-type devices, the following can be noted:
a) exceptionally high speed of information processing, b) the ability to quickly enter and encrypt a previously prepared text, c) the possibility of using complex and extremely strong encryption algorithms, d) good compatibility with modern communication facilities, e) fast visualization of text with the ability to quickly print or erase it, f) the ability to have in one computer various encryption programs with blocking access to them
unauthorized persons using a password system or internal crypto protection, g) the universality of the encrypted material (i.e., under certain conditions, a computer encryption algorithm can encrypt not only alphanumeric information, but also telephone conversations, photographic documents and video materials).
However, it should be noted that the organization of information protection during its development, storage, transmission and processing should adhere to a systematic approach. There are many possible ways of information leakage, and even good crypto protection does not guarantee its security unless other measures are taken to protect it.
References:
Adamenko M. Foundations of classical cryptology. Secrets of ciphers and codes. M.: DMK press, 2012. S. 67-69, 143, 233-236.
Simon S. The Book of Ciphers. M.: Avanta +, 2009. S. 18-19, 67, 103, 328-329, 361, 425.
