Explanatory dictionaries give us close to each other semantic definitions of the term “cryptography”, differing only in the fields of its application. Cryptography is the science of ways to protect information through various methods, if necessary, restricting the authority to familiarize yourself with it and use it.
Cryptographic methods of information protection are the transformation of information for its further transfer to an authorized person. The principle of these methods is as follows. The primary open message is encrypted, taking the form of a closed text or graphic image, called a cipher program. Further, the cipher program is transmitted via a secure or insecure channel for transmitting information to the point of receipt. The authorized user performs the inverse transformation or decryption of the received message and receives the original plaintext. Thus, an unauthorized person who intercepted the cipher program will not be able to read it, not knowing which cryptographic methods of information protection were used during encryption.
In cryptography, the concept of a key is often used, which allows us to draw a parallel between encrypted information and the encoding system. Cryptographic information protection tools use a unique sequence of characters for encryption and decryption, which is called the key. Thus, when using the same cryptographic encryption algorithm, the result depends on the key.
Keys according to their classification are divided into:
- symmetric, that is, the sender and recipient use the same key in the process of encryption and decryption, which ensures high confidentiality of the encrypted message, but creates problems when the keys function in various systems where there are a large number of users;
- asymmetric, in fact it is considered a key pair in which the private (secret) and public keys are provided.
The principle of a key pair is as follows: a secret key is used to generate a public key, but cannot be generated back from a known public key. This ensures authentication verification when transmitting information signed with an electronic digital signature (EDS).
Means of cryptographic protection of information using asymmetric keys are effective in encrypting transmitted rather than stored information. Public keys are great for replacing a conventional signature with an electronic (digital) one, which is widely used in Internet payment systems.
Cryptographic methods of information protection must satisfy the following requirements:
- Have a robust cipher that can withstand cryptanalysis and provide a way to open it only by exhaustive search of keys. Therefore, the probability of determining a key depends on its length.
- Ensure the strength of the cryptographic system by storing secret keys securely, rather than algorithms that use them.
- Generate the amount of encoded information that does not exceed the original.
- Eliminate distortion and loss of information due to errors that occur during encryption.
- Provide minimum coding time.
- Have a consistency between the cost of encryption and the cost of the source information.
Cryptographic methods of information protection are characterized by the stability of the cipher, which is the main indicator of effectiveness. This efficiency consists in the time or cost of the funds needed for the decryptor to receive the original message from the encoded key in the absence of a key. Given the absence of weaknesses in encryption algorithms that can be quickly calculated by craftsmen and a sufficiently reliable key length, these costs grow significantly.