Crypto history

Man is a social being, for many millennia he has been living in a society of his own kind. And it is quite natural that one of his most important abilities is the ability to communicate with other people - to convey to them information about what is happening in the world around them, and about the facts of their subjective reality. The second signaling system - speech - is rightfully considered to be one of the most important distinguishing features that qualitatively distinguishes humanity from the animal world. The nature of information exchange between members of even the wildest tribe is many times more complex than anything that can be seen in animals. Communication in human society has another distinctive feature - it is narrowly selective. We talk to different people in completely different ways, and try to hide what we tell one from others.

Thus, with the birth of human civilization, the ability to communicate information to one people in such a way that it does not become known to others has arisen. As long as people used only voice and gestures to transmit messages, it was usually not difficult to do this - it was necessary only to exclude the presence in the immediate vicinity of people who were talking and for whom the information was not intended. However, sometimes external factors imposed restrictions on the behavior of interlocutors, which did not allow them to hide from prying ears and eyes to conduct confidential conversations. For action in such circumstances was created, or rather formed by itself, a system coded by speech or gestures of messages. In various situations, she wore a completely different character - from a separate secret sign, speaking about the occurrence of a certain event, to developed secret languages, which allowed expressing thoughts of almost any complexity. Even in the simplest case, it was in its essence a second miniature gnosis system designed to convey limited information and generally known only to a small group of initiates, a fragment, large or small, of an alternative language, and it was she who initiated the art that developed later send messages.

Of course, the use of a developed “secret” language to protect transmitted data provides much greater freedom of communication than a few secret signs that the participants agreed on the day before, but this path also has much higher costs. It is difficult to keep track of all the initiates, and sooner or later such a language will become understandable to those who are trying to hide the conversation. In this case, it will be necessary to replace it with another, but it is very difficult and costly to develop a sufficiently powerful language and teach it to the necessary number of people, and it is impossible to do it quickly. Therefore, a similar approach to the problem takes place only in special cases when circumstances favor it. So, it was used by the Americans during the Second World War: US Navy ships communicated in the language of a small and compact Indian nation. On each ship there were several Indians, "cryptographers," the enemy had virtually no chance of obtaining such a "cryptographer" for themselves.

With the advent of writing, the task of ensuring the secrecy and authenticity of transmitted messages has become particularly relevant. Indeed, a message transmitted verbally or indicated by gestures is accessible to an outsider only during that short period of time while it is “on the way”, and the recipient cannot be in any doubt about his authorship or authenticity, because he sees his interlocutor. It is a different matter when a message is recorded - it already lives a separate life and has its own path, often far from the path of the person who created it. A message recorded on paper exists in the material world for a much longer period of time, and people who want to familiarize themselves with its contents against the will of the sender and the recipient, are much more likely to do so. Therefore, it was after the emergence of writing that the art of secret writing appeared, the art of "secretly writing" —a set of methods intended for the secret transmission of recorded messages from one person to another.

Data on the first methods of cryptography is very fragmentary. It is assumed that she was known in ancient Egypt and Babylon. Until our time came the indications that the art of secret writing was used in ancient Greece. The first really reliable information describing the encryption method refers to the period of the change of the old and the new era and describes Caesar's cipher - the way that Julius Caesar hid his notes from curious eyes. From the heights of the achievements of modern cryptography, Caesar’s cipher is extremely primitive: in it, each letter of the message was replaced with the next letter in alphabetical order. However, for the time when the ability to read and write was a rare exception, its cryptographic strength was enough. The use of cipher solved the problem of the secrecy of the transmitted message, and the problem of its authenticity was solved almost by itself:
firstly, for a person who did not know the cipher, it was impossible to make meaningful changes to the encrypted messages that were purely textual, and changes made at random resulted in a meaningless set of letters after decryption;
secondly, almost to the times still quite recent by historical standards, the sent messages were recorded by hand, and each person has his own individual, unique to him handwriting, which is very difficult for another person to reproduce; It’s not difficult to memorize the handwriting of even a few dozen of the most important correspondents - and no one else had it -.

Humanity has invented a large number of secret writing methods, many of which were known in antiquity. In some methods of secret writing uses the physical characteristics of the media. So the sympathetic ink disappears soon after writing the text or is invisible from the very beginning. But they can again be made visible by processing the document with a special chemical reagent or by illuminating with rays of a certain part of the spectrum, usually with ultraviolet light. Steganography assumes that the transmitted text "dissolves" in a larger message with a completely "extraneous" meaning. But if we take and extract some symbols from it according to a certain law, for example, every second, or third, etc., we get a very specific secret message. Encryption is the conversion of a message according to certain rules, which makes it a meaningless set of characters for the uninitiated person to the secret code.

There are two ways to classify ways of classifying transmitted messages, but there are only two determining factors:
Whether properties of material carriers and the material medium of information transfer are used for classifying information or is it carried out independently of them;
Is the secret message hidden or is it simply made inaccessible to everyone except the recipient.

As noted above, a large number of ways to classify a message is associated with an effect on its carrier as a material object. This is a very interesting topic, but it is a subject of study of physics and chemistry, and has nothing to do with information theory. For mass practical application, methods of data protection are of much greater interest, which rely solely on the properties of the data themselves and are in no way connected with the peculiarities of their physical representation. Figuratively speaking, when using methods of this type, the barrier between the actual message and the attacker who wants to read or distort it is erected solely from the information itself. In the future, only such methods of protection will be discussed.

Depending on the answer to the second of the above questions, different classes of data classification methods are obtained - steganography and encryption. If we consider information separately from its material representation, then where is it then possible to hide it? The answer is unequivocal: only in an even greater array of information - like a needle in a haystack. This is the principle of steganography. For example, we send to our correspondent by e-mail a file with a raster black and white image in which the least significant bit in the brightness code of each image point will be an element of our secret message. The recipient of the letter will extract all such bits and make up the "true" message. The picture, which is present here only for eye removal, will remain for the uninitiated a simple picture. Steganography is useful when it is necessary not only to transmit a secret message, but to secretly transmit a secret message, that is, to hide the fact that a secret message has been transmitted. This way of conducting secret communication, however, has several disadvantages:
firstly, it is difficult to substantiate its resilience - suddenly attackers will become aware of a method of "mixing" secret data to a "pig" - an array of open data;
secondly, when it is used, the volume of transmitted or stored data increases dramatically, which adversely affects the performance of their processing systems;

Another approach is not to hide the fact that the message was transmitted, but to make it inaccessible to an outsider. To do this, the message must be recorded so that no one except the correspondents themselves could familiarize themselves with its contents - this is the essence of encryption. And cryptography arose precisely as a practical discipline that studies and develops ways to encrypt messages.

Let's go back to the story. The more lively correspondence was conducted in society, the greater the need was felt for the means of classifying it. Accordingly, there appeared more sophisticated and sophisticated ciphers. First, cryptographers appeared with interested persons, then groups of several cryptographers, and then entire cryptographic departments. When the volumes of information to be closed became critical, mechanical encryption devices were created to help people. It should be noted that the main consumers of cryptographic services were diplomatic and espionage missions, secret offices of the rulers and the headquarters of military units. For this stage of cryptography development, the following is characteristic:
only text messages written in natural languages ​​were protected — there was simply no other type of discrete data presented;
Encryption was first carried out manually; later, relatively simple mechanical devices were invented, so the ciphers used at that time were fairly simple and uncomplicated;
cryptography and cryptanalysis were more art than science, there was no scientific approach to building ciphers and their disclosure;
cryptography was used in very narrow areas - only to serve the upper ruling strata and the military elite of the states;
The main task of cryptography was to protect transmitted messages from unauthorized access to them, since only text messages were encrypted, no additional methods of protection against the imposition of false data were used - the probability of obtaining something meaningful after decrypting the distorted ciphertext was negligible because of the enormous redundancy typical of natural languages.

The appearance in the middle of our century of the first electronic computers radically changed the situation. With the penetration of computers into various spheres of life, a fundamentally new branch of the economy has emerged - the information industry. The volume of information circulating in society has steadily increased exponentially since then — it roughly doubles every five years. In fact, on the threshold of the new millennium, mankind has created an information civilization, in which the very well-being and even the survival of mankind in its current capacity depends on the successful operation of information processing tools. The changes that occurred during this period can be characterized as follows:
the volume of information processed increased by several orders over half a century;
there is such a situation that access to certain data allows you to control significant material and financial values; information has gained value, which in many cases can even be calculated;
the nature of the data being processed has become extremely diverse and is no longer limited to textual data only;
the information is completely "depersonalized," i. the features of its material representation have lost their meaning - compare the letter of the past century and the modern e-mail message;
the nature of information interactions has become extremely complicated, and along with the classical task of protecting transmitted text messages from unauthorized reading and misrepresentation, new tasks in the field of information protection have arisen and were previously solved within the framework of used "paper" technologies - for example, signing an electronic document and handing an electronic document " on receipt "- talking about these" new "tasks of cryptography is still ahead;
The subjects of information processes are now not only people, but also automatic systems created by them, operating according to the program incorporated in them;
the computational "abilities" of modern computers have raised to a completely new level both the possibilities for implementing ciphers, previously unthinkable because of their high complexity, and the ability of analysts to crack them.

The above changes led to the fact that very quickly after the spread of computers in the business sphere, practical cryptography made a huge leap in its development, and in several directions at once:
first, robust block ciphers with a secret key were developed to solve the classical problem of ensuring the secrecy and integrity of the transmitted or stored data, they still remain the "working horse" of cryptography, the most frequently used means of cryptographic protection;
secondly, methods were created for solving new, non-traditional tasks in the field of information security, the most well-known of which are the task of signing a digital document and public distribution of keys.
As you can see, the term "cryptography" has gone far from its original meaning - "secret writing", "secret letter". Today, this discipline combines methods of protecting information interactions of a completely different nature, based on the transformation of data by secret algorithms, including algorithms that use secret parameters. The term "information interaction" or "information interaction process" here means such a process of interaction of two or more subjects, the main content of which is the transfer and / or processing of information. By and large, any data conversion function, secret in itself or dependent on secret parameter S, can be considered cryptographic:
T '= f (T), or
T '= f (T, S).