Since ancient times, people have sought to create the ability to protect various information from prying eyes by converting it. Cryptography can be considered the same age as the emergence of human language. Initially, writing was a cryptographic system, not without reason in ancient time only a few people knew her. Ancient Egyptian and Ancient Indian manuscripts can testify to this fact. So cryptography is specific method information protection, which has long history development. And cryptology is a kind of trend that deals with scientific study and development of methods, techniques, means of cryptographic encryption of information.
Cryptology is a scientific movement that studies the issues of secure communication using encrypted sentences. This science is divided into 2 directions.
- Cryptography is a science that studies a secure communication technique, the creation of secure systems that provide encryption. This section is responsible for finding a technique for changing information using mathematics.
- Cryptanalysis is a branch that explores the possibility of reading text without using a key, that is, it studies the possibilities of breaking.
Cryptanalysts are people who study cryptanalysis and research developed ciphers.
Cipher - reversible substitution system plaintext different variation of ciphertexts, which is necessary to protect messages.
Encryption is the process of using ciphers with respect to a message.
Decryption is the reverse process of applying an encryption system to a modified letter.
Decryption - reading a message without using a key, in other words, breaking a message edited by a cipher.
How cryptology developed, and the main stages of modification
In 1987, throughout the United States of America for use by the general public, national standard cryptography, after 2 years such encryption of information was adopted in Russia.
There are 3 stages in the development of this scientific trend. The first of these is the time of pre-scientific cryptology, which was distributed among a few skilled craftsmen and was a craft. The second stage dates back to 1949, namely the release of the work of K. Shannon, which considers communication in secret systems. In this work, the researcher fundamentally studies ciphers and the most important questions arising from their stability. This work became Starting point, with which cryptology is beginning to be considered an applied mathematical discipline. The third period begins with the release of labor " The latest destinations in cryptography”, which was distributed in 1976 by researchers W. Diffie and M. Hellman. In this work, the possibility of secret communication without the prior distribution of a secret key encryption method was shown.
In this video, you can learn how the Diffie and Hellman algorithm works with a simple and understandable example.
Cryptology as a science: the history of the emergence of BC
In ancient times, when the possibility of writing belonged to a few people, it was perceived as a method of hiding information. In the 10th century BC, ancient ciphertexts appeared, which were found during archaeological excavations in Mesopotamia. The message was written on a clay tablet, it contained a recipe for mixing glaze for processing ceramic products.
In the middle of the 9th century BC, a scytale, a device for encryption, began to be used. The scytal operated on the basis of encryption with a permutation. To decipher the text, it was necessary to wind the resulting tape around the cone. In the place where they formed readable words, the required diameter was determined, with the help of which it was read full text. This method was invented by Aristotle.
In 56 BC, Julius Caesar actively used the substitution cipher. It consisted in rewriting the alphabet with a shift along a certain numerical cycle under the alphabet open letter. The symbols of the open message, located on top, were replaced by symbols of the lower alphabet.
Development history: our era
In the 5th century, the decline of cryptographic development was observed. This is due to the church's persecution of cryptography, which it perceived as witchcraft. This was due to the fact that the encrypted thoughts were not available for reading by church officials.
R. Bacon considered 7 systems of cipher writing. At that time a large number of secret writing techniques were used to conceal scientific research.
In the second half of the 15th century, the mathematician L.B. Albert wrote a book while in the Vatican. In this work, cipher replacements using 2 concentric circles were considered. An open alphabet was depicted around the perimeter of one circle, and an encrypted system was depicted along the perimeter of the other.
I. Tritemius wrote a textbook on cryptography, which turned out to be the first work of such content. It was he who proposed the method of encryption "Ave Maria" using a multi-valued replacement. In this technique, each letter symbol text had a variation of substitutions. At the end of encryption, a pseudo-open letter was obtained.
D. Cardano invented an encryption system, which was based on the use of a cardboard piece, where the lattice was marked, and there were holes that were numbered in random order. To receive a modified message, it was necessary to write letters in the holes in accordance with the chosen numbering.
History of development since the 17th century
Lord F. Bacon first began to encrypt letters using a 5-digit binary code consisting of 0 and 1.
In the 17th century, dictionary encryption techniques were invented, in which letter designations were written in 2 numbers - the number number of the line and the specific number of the letter in the line of the selected common book.
K. Gauss used a random encryption of the message. In it, frequently occurring symbols were replaced by the letter designations of the corresponding groups.
Until our time, cryptographic research has been used to preserve the secrets of the state, so special bodies have developed resistant systems. Nowadays, the sphere of information security is actively expanding its boundaries. It becomes relevant to carry out system analysis means of cryptography, taking into account possible option them active use to keep secrets in different conditions. Also last years development of cryptology are distinguished by the development the latest techniques encryption of data that can be most actively used to modify the letter in comparison with traditional cryptographic encryption.
In this video, you can learn about what cryptography is, asymmetric and asymmetric encryption in an understandable and accessible language. Be sure to leave your questions and wishes in
Since the advent of writing, such an industry has developed scientific knowledge as poleography- historical and philological discipline that studies monuments ancient writing in order to establish the place and time of their creation. The knowledge of poleography is also based on the study of abbreviations of writing and cryptography, methods of their decoding. All this led to the emergence of a new direction of scientific knowledge of poleography, which, in turn, led to the formation of a scientific and applied direction - cryptology(crypto-kriptos (Greek) - secret, hidden; logic-logike (Greek) - section scientific knowledge about methods of evidence and refutation). However, this concept in the applied aspect of the theory of information transmission is interpreted as the science of creating and analyzing secure communication systems. Such a definition, far from fully, characterizes the fundamental and applied semantics of the scientific direction - cryptology, but is only a small specific structural component. More complete scientific direction"cryptology" should be interpreted as the science of coding semantic statements.
In turn, the scientific direction "cryptology" is divided into three functionally dependent logical-mathematical and technical directions Key words: cryptography, cryptanalysis, steganography.
Cryptography(Greek kriptos - secret, hidden; graho - I write) - the science of methods for protecting information based on its transformation using various ciphers and maintaining the reliability of the semantic content.
Cryptography is a branch of the science of poleography that studies the graphics of cryptography systems. Based on the modern positions of the theory of information transmission and coding theory, cryptography is defined as a branch of scientific knowledge about methods for ensuring the secrecy and reliability of data during transmission over communication channels and their storage in operative and long-term memory devices.
Cryptanalysis(Greek kriptos - secret, hidden; analysis - decomposition) – the science of methods for disclosing and modifying data. This scientific direction has two goals as the subject of its study.
The first goal is the study of encrypted information in order to restore the semantic content of the original content without knowing the encryption key (conceptual recognition).
The second goal is to falsify source documents based on the study and recognition of cryptography methods in order to transmit false information.
Steganography(stega-brand; graho-write) - a method of information transformation that hides the very fact of transmitting a message, a method based on the principle of intelligence security of confidential messages. In this case, the original message can be presented in the form of a speech signal, a musical melody, a video image signal, or another text document.
Cryptography as applied Science has developed since the 20th century BC. For example, during excavations ancient civilization found in Mesopotamia clay tablets containing cryptographic writing about the glazing of pottery, i.e. the first ciphertexts were of some commercial nature. Later, texts of a medical nature, purchase and sale of livestock and real estate began to be encrypted. The preparation and transmission of ciphertexts were further developed during the conduct of hostilities. The relative large scale of military activities has led to the need to develop and implement "small-scale mechanization" for encrypting secret messages. Known historical fact, described by the ancient Greek writer and historian Plutarch (the author of " Comparative biographies”, containing 50 biographies of prominent Greeks and Romans), on the implementation of the encryption operation using the “small-scale mechanization tool” - the “skital” encryption device. A cylinder of a given diameter was chosen as an encryption device, on which a strip of paper tape was wound. The original text was recorded on this tape, then the tape was unwound from the cylinder and into the spaces between the letters (L = 2PR) source code letters of the natural alphabet were entered arbitrarily. Thus, an unauthorized user could not read the encrypted message and recognize the original text without knowing the diameter of the cylinder. The key to access the encrypted information was the diameter of the cylinder, which served as both a cipher-forming mechanism and a decryption device. In this case, the decrypting device was a cylinder of the same diameter as in the case of encryption. A paper tape with the ciphertext written on it was wound around this cylinder, and the ciphertext was deciphered.
This method was the prototype of modern symmetric cryptographic systems (single-key encryption-decryption systems).
This method and the encryption-decryption device itself served for quite a long time, until the ancient Greek philosopher and scientist Aristotle showed himself as a cryptanalyst and proposed using a cone as a cryptanalytic device for recognizing the diameter of a cylinder (scytal - the encryption-decryption key) encrypted tape. The place on the cylinder where it formed readable part words or full word, determined the diameter of the cylinder (wanderer).
The active conduct of hostilities was a powerful stimulating effect on the development of encryption-decryption methods for the transmission of secret messages. So, in 56 BC, during the war with the Gauls, the Roman dictator C. Caesar, while subordinating transalpine Gaul to Rome, used substitution ciphers in the system for transmitting secret messages. Such encryption-decryption methods were "Caesar cipher with offset", "Caesar cipher with keyword», « affine system substitutions”, etc.
AT late XIX centuries, mechanical encryption devices have appeared that work according to the replacement method: the Bolton encryption wheel; cipher M-94, which was in service american army from 1924 to 1943. A further modification of the M-94 product was the M-209 encryption machine, which was developed by the Swedish cryptographer B. Hagelin in 1934 on the instructions of the French special services. This cipher machine was produced in a series of more than 140 thousand pieces and was in service with the American army during the Second World War. Enough powerful development encryption mechanism received and in Nazi Germany when creating the Enigma cipher machine.
The centuries-old history of the development of the science of cryptography shows that relatively until recently, it was aimed at building cryptographic systems for military purposes. However, in recent decades this scientific direction has found wide application in almost all areas human activity, performing functions as cryptographic protection electronic messages from unauthorized perception and recognition, and authentication (authentication) of received electronic messages using electronic digital signature tools.
In one of his works “Applied Cryptography”, the American scientist Bruce Schneier fully characterized the importance of cryptography in one sentence. present stage development information technologies. He noted that: "Encryption is too important to be left only to governments." Cryptographic tools are the only and highly reliable method that ensures the protection of information in network computer technology different levels and appointments. The relevance of this direction is an unambiguously unconditional undeniable factor in all areas of public administration and commercial activities: defense, law enforcement, economic, banking, commercial, educational, etc.
When cryptographing open electronic messages when transmitting them through open public channels, including Internet technology channels, there are three main methods:
Symmetric (single-key) conversion method open messages;
Asymmetric (two-key) method of converting open messages (public key cryptography);
Combined method transformations of open messages.
The most widespread in open network computer technologies at the present stage of development and operation of cryptographic protection and authentication systems electronic documents and messages received combined cryptographic systems that combine the advantages of symmetric and asymmetric transformations.
The method of asymmetric transformation of open messages is implemented in cryptographic systems with a public key. Further development method of asymmetric transformation, which has received the most widespread at the present stage and is defined as the most promising, a method for constructing cryptographic systems based on theoretical provisions elliptic curves. Initially, the theory of building cryptographic systems based on asymmetric methods must be considered in the basis of public key cryptosystems.
Chapter two - "Definitions and Classification" - is also very brief, speaks for itself. It provides definitions and some discussion of the basic concepts of modern cryptology. The two best known such candidates were designed shortly after Diffie and Hellman introduced the concept of public-key cryptography. One of them, the so-called Merkle knapsack cryptosystem (R.C. Randomness and cryptography are very closely related. The main goal of cryptosystems is to transform non-random meaningful plaintexts into a seemingly random mess. Public-key cryptography largely solves the key distribution problem, which is quite serious for cryptography with a secret key.The probabilistic encryption system used in this way in to some extent very similar to a public key system.
And cryptology is a kind of trend that is engaged in the scientific study and development of methods, techniques, means of cryptographic encryption of information. Cryptology is a scientific movement that studies the issues of secure communication using encrypted sentences. Cryptography is a science that studies a secure communication technique, the creation of secure systems that provide encryption. Cryptanalysis is a branch that explores the possibility of reading text without using a key, that is, it studies the possibilities of breaking.
Cryptology and cryptography
Applied cryptography, as the name suggests, is more concerned with applying the achievements of theoretical cryptography to the needs of specific applications in practice. 1.1. The first concepts of cryptology. Cryptology is usually divided into two parts: cryptography and cryptanalysis, in accordance with the aspects of synthesis and analysis. Cryptography is the science of security methods, that is, it is more concerned with the synthesis of systems. We have a different terminology in our country, when the term "cryptography" was used to name the whole science, and cryptanalysis was called decryption.
Cryptology consists of two parts - cryptography and cryptanalysis.
The second stage dates back to 1949, namely the release of the work of K. Shannon, which considers communication in secret systems. In this work, the researcher fundamentally studies ciphers and the most important questions arising from their stability. The third period begins with the release of the work "Recent Trends in Cryptography", which was distributed in 1976 by researchers W. Diffie and M. Hellman. In the middle of the 9th century BC, a scytale, a device for encryption, began to be used. R. Bacon considered 7 systems of cipher writing. During this time, a large number of secret writing techniques were used to cover up scientific research. I. Tritemius wrote a textbook on cryptography, which turned out to be the first work of such content.
Cryptology and the main stages of its development.
The following three periods of development of cryptology can be distinguished. The first period is the era of pre-scientific cryptology, which was a craft - a lot narrow circle skilled craftsmen. The beginning of the second period can be considered 1949, when the work of K. Shannon "Theory of Communication in Secret Systems" appeared, in which a fundamental Scientific research ciphers and critical issues their resilience. Thanks to this work, cryptology took shape as applied mathematical discipline. And, finally, the beginning of the third period was laid by the appearance in 1976 of the work of W. Diffie, M. Hellman "New Directions in Cryptography", which shows that secret communication is possible without prior transmission of the secret key. This is how it started and continues to this day. rapid development along with conventional classical cryptography and public key cryptography.
A few centuries ago, the very use of writing could be regarded as a way of hiding information, since the possession of writing was the lot of a few.
The problem of protecting information by transforming it is dealt with cryptology(kryptos - secret, logos - science). Cryptology is divided into two areas - cryptography and cryptoanalysis. The goals of these directions are directly opposite.
Cryptography engages in exploration and research mathematical methods information transformation. This is the concealment of the meaning of the message by means of encryption and its disclosure by means of decryption.
Area of interest cryptanalysis - study of the possibility of decrypting information without knowing the keys.
Modern cryptography includes four major section:
1. Symmetric cryptosystems.
2. Cryptosystems with a public key
3. Electronic signature systems.
4. Key management.
The main directions of using cryptographic methods are the transfer of confidential information over communication channels (for example, Email), authentication of transmitted messages, storage of information (documents, databases) on media in encrypted form.
Cryptographic methods for protecting information in automated systems can be used both to protect information processed in a computer or stored in various types memory, and to close the information transmitted between various elements communication lines. Cryptographic transformation as a method of preventing unauthorized access to information has centuries of history. At present, a large number of various methods encryption, theoretical and practical foundations their applications. The vast majority of these methods can be successfully used to close information.
Cryptographic Data Transformation Methods
So, cryptography makes it possible to transform information in such a way that its reading (restoration) is possible only if the key is known.
Let us first list some basic concepts and definitions.
Alphabet - a finite set of signs used to encode information.
Text - an ordered set of alphabetic elements.
The following are examples of alphabets used in modern IS:
alphabet Z 33 - 32 letters of the Russian alphabet and a space;
alphabet Z 256 - characters included in the standard codes ASCII and KOI-8;
binary alphabet - Z 2 = (0,1); octal or hexadecimal alphabet.
Encryption is a transformative process: the original text, which is also called plaintext, is replaced by ciphertext.
Decryption - reverse encryption process. Based on the key, the ciphertext is converted to the original.
Key - information necessary for the smooth encryption and decryption of texts.
Rice. 3.1. File Encryption Procedure
Cryptographic system is a family of Ttransformations of the plaintext. Members of this family are indexed or denoted by k; parameter k is key.
Key space TO - this is a set possible values key. Usually the key is a consecutive series of letters of the alphabet.
Cryptosystems are divided into symmetric and public key.
AT symmetric cryptosystems used for both encryption and decryption one and that is my key.
AT public key systems two keys are used - public and private, which are mathematically related to each other. Information is encrypted using a public key, which is available to everyone, and decrypted using a private key, known only to the recipient of the message.
There are two main methods encryption: symmetric and asymmetric. In the first of these, the same key (kept secret) is used for both encryption and decryption data. Very efficient (fast and reliable) methods of symmetric encryption have been developed.
Rice. 11.1. Using a symmetric encryption method
The main disadvantage of symmetric encryption is that The secret key must be known to both the sender and the recipient. On the one hand, this creates new problem distribution of keys. On the other hand, the recipient, based on the presence of an encrypted and decrypted message, cannot prove that he received this message from a specific sender, since he could generate the same message on his own.
Asymmetric methods use two keys. One of them, non-secret (it can be published together with other public information about the user), is used for encryption, the other (secret, known only to the recipient) is used for decryption. The most popular of the asymmetric ones is the RSA (Rivest, Shamir, Adleman) method, which is based on operations on large (say, 100-digit) prime numbers and their works.
Let's illustrate the use of asymmetric encryption (see Figure 11.2).
Rice. 11.2. Using an asymmetric encryption method.
A significant disadvantage of asymmetric encryption methods is their low performance, so these methods have to be combined with symmetric ones (asymmetric methods are 3–4 orders of magnitude slower). So, to solve the problem of efficient encryption with the transfer of the secret key used by the sender, the message is first symmetrically encrypted with a random key, then this key is encrypted with the recipient's public asymmetric key, after which the message and the key are sent over the network.
Terms "key distribution" and "key management" refer to the processes of the information processing system, the content of which is the compilation and distribution of keys between users.
Electronic (digital) signature called its cryptographic transformation attached to the text, which allows, upon receipt of the text by another user, to verify the authorship and authenticity of the message.
Crypto resistance is called a characteristic of a cipher that determines its resistance to decryption without knowing the key (i.e., cryptanalysis). There are several indicators of cryptographic strength, including:
the number of all possible keys;
average time required for cryptanalysis.
transformation T to,. is determined by the corresponding algorithm and the value of the parameter k. The effectiveness of encryption to protect information depends on maintaining the secret of the key and the cryptographic strength of the cipher.
The process of cryptographic closing of data can be carried out both in software and in hardware. The hardware implementation is significantly more expensive, but it also has advantages: high performance, simplicity, security, etc. Software Implementation is more practical, allowing a certain flexibility in use.
For modern cryptographic information security systems, the following generally accepted requirements are formulated:
the encrypted message must be readable only if the key is present;
the number of operations required to determine the used encryption key from a fragment of an encrypted message and the corresponding plaintext must be at least total number possible keys;
the number of operations required to decrypt information by searching through all possible keys must have a strict lower estimate and go beyond the capabilities of modern computers (taking into account the possibility of using network computing);
knowledge of the encryption algorithm should not affect the reliability of the protection;
a slight change in the key should lead to a significant change in the form of the encrypted message, even when using the same key;
structural elements encryption algorithms must be unchanged;
additional bits introduced into the message during the encryption process must be completely and securely hidden in the ciphertext;
the length of the ciphertext must be equal to the length original text;
there should be no simple and easily established dependencies between the keys sequentially used in the encryption process;
any key from the set of possible ones must provide reliable protection of information;
the algorithm should allow both software and hardware implementation, while changing the key length should not lead to a qualitative deterioration of the encryption algorithm.
Consider the classification of cryptographic closure algorithms.
1 Encryption
1.1 REPLACEMENT (SUBSTITUTION)
1.1.1. Simple (one-alphabetic) 1.1.2. Multi-alphabetic single-circuit ordinary 1.1:3. Multi-alphabetic single loop monophonic
1. 1.4. Polyalphabetic multiloop
1.2. REPLACEMENT
1.2.1. Simple 1.2.2. Complicated according to table 1.2.3. Complicated on routes
1.3. ANALYTICAL CONVERSION
1.3.1. Using Matrix Algebra
1.3.2. For special dependencies
1.4. GAMMING
1.4.1. With finite short scale
1.4.2. With finite long gamma
1.4.3. With an endless range
1.5. COMBINED METHODS
1.5.1. Replacement and permutation 1.5.2. Substitution and scaling 1.5.3. Permutation and gamming
1.5.4. Gamming and gamming
2. Encoding
2.1. semantic
2.1.1. According to special tables (dictionaries)
2.2. SYMBOLIC
2.2.1. By code alphabet
3. Other types
3.1. CUT-EXPLORE
3.1.1. Semantic 3.1.2. Mechanical
3.2. COMPRESSION-EXPANSION
Under encryption this type of cryptographic closure is understood, in which each character of the protected message is subjected to transformation. All known ways encryption can be divided into five groups: substitution (replacement), permutation, analytical transformation, gamma and combined encryption. Each of these methods can have several varieties.
Under coding this type of cryptographic closure is understood when some elements of the protected data (these are not necessarily individual characters) are replaced by pre-selected codes (numeric, alphabetic, alphanumeric combinations, etc.). This method has two varieties: semantic and symbolic coding. With semantic coding, the encoded elements have completely certain meaning(words, sentences, groups of sentences). In character encoding, each character of the protected message is encoded. Symbolic encoding is essentially the same as substitution encryption.
Polyalphabetic substitution - the simplest type of transformation, which consists in replacing the characters of the source text with others (of the same alphabet), more or less complicated rule. To ensure high cryptographic strength, the use of large keys is required.
Permutations - a simple method of cryptographic transformation. It is used, as a rule, in combination with other methods.
Gambling - this method consists in imposing on the source text some pseudo-random sequence generated on the basis of the key.
Block ciphers represent a sequence (with possible repetition and alternation) of the main transformation methods applied to a block (part) of the encrypted text. In practice, block ciphers are more common than "pure" transformations of one class or another due to their higher cryptographic strength. Russian and American encryption standards are based on this particular class of ciphers.
To certain types cryptographic closing methods are assigned slicing-expanding and data compression Dissection-expansion consists in the fact that the array of protected data is divided (dissected) into such elements, each of which individually does not allow revealing the content of the protected information. The data elements selected in this way are distributed over different memory zones or are located on various media. Data compression is the replacement of frequently occurring identical strings of data or sequences of identical characters with some pre-selected characters.
Secret encrypted messages in order to protect the content of the text arose in ancient times at the dawn of civilization. There is evidence that the methods of secret writing were already known to the ancient civilizations of India, Egypt and Mesopotamia.
Nowadays, the science of cryptology is engaged in encryption and decryption methods (from other Greek κρυπτoς - hidden and λoγος - word). Cryptology consists of two parts - cryptography and cryptanalysis. Cryptography deals with the development of methods for encrypting data, while cryptanalysis deals with the evaluation of strong and weaknesses encryption methods, as well as the development of methods that allow breaking cryptosystems.
The word cryptology is found in English language since the 17th century, and originally meant "secrecy in speech"; in modern meaning was introduced by the American scientist William Friedman and popularized by the writer David Kahn.
The history of cryptography, numbering about 4 thousand years, can be divided into several periods depending on the encryption methods used.
The first period (approximately from the 3rd millennium BC) is characterized by the dominance of monoalphabetic ciphers (the main principle is the replacement of the alphabet of the original text with another alphabet by replacing letters with other letters or symbols).
The second period (from the 9th century in the Middle East (Al-Kindi) and from the 15th century in Europe (Leon Battista Alberti) to the beginning of the 20th century) was marked by the introduction of polyalphabetic ciphers.
The third period (from the beginning to the middle of the 20th century) is characterized by the introduction of electromechanical devices into the work of cryptographers. At the same time, the use of polyalphabetic ciphers continued.
The fourth period (from the middle to the 70s of the XX century) is the period of transition to mathematical cryptography. In Shannon's work, strict mathematical definitions quantity of information, data transmission, entropy, encryption functions. An obligatory step in creating a cipher is the study of its vulnerability to various well-known attacks - linear and differential cryptanalysis. Until 1975, however, cryptography remained "classical" (secret-key cryptography).
Fifth, modern period development of cryptography (from the late 1970s to the present) is characterized by the emergence of public-key cryptography. Its appearance is marked not only by new technical capabilities, but also by the relatively wide spread of cryptography for use by private individuals. Legal regulation use of cryptography by individuals in different countries varies greatly - from permission to a total ban.
Modern cryptography forms a separate scientific direction at the intersection of mathematics and computer science - works in this area are published in scientific journals regular conferences are organized. Practical use cryptography has become an integral part of life modern society- it is used in such industries as e-commerce, electronic document management (including digital signatures), telecommunications and others.
