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Encryption is one of the main (and probably the most effective) methods of protecting data confidentiality, i.e. encryption algorithm involving a unique element - encryption key ), which is called encryption ; decryption , a certain key is also involved in this operation. Encryption is one of the main (and probably the most effective) methods of protecting data confidentiality, i.e. encryption algorithm involving a unique element - encryption key ), which is called encryption ; decryption , a certain key is also involved in this operation. The encryption key is related by a certain relationship to the decryption key; symmetric encryption The encryption key “personalizes” the encryption algorithm - without knowing the required encryption key, it is quite difficult to decrypt the data. cryptographic strength The science of countering cryptographic methods of protection (which includes encryption) is called cryptanalysis .
Attacks on encryption algorithms When carrying out an attack, a cryptanalyst can aim to solve the following problems: 1.Obtaining plaintext from encrypted text. 2. Calculation of the encryption key. In general, the second of the listed tasks is significantly more complex than the first. full disclosure encryption algorithm. Attacks on encryption algorithms are usually classified depending on the set of information that the attacker has before carrying out his attack. Category 1. The cryptanalyst only has the ability to passively listen to a certain channel through which encrypted data is sent (see Fig. 1). known ciphertext . Rice. Category 2. Assumes that the cryptanalyst has some kind of encryption device with an encryption key embedded, which is the target of the attack. Rice. Depending on the data that a cryptanalyst can “extract” from the encryptor, there are the following types of attacks: 1. Known Plaintext Attack . 2. Chosen Plaintext Attack . .Adaptive plaintext attack . 4. Ciphertext selection attack . 5. Adaptive ciphertext selection attack. By analogy with the attacks described earlier, it is clear that a cryptanalyst can repeatedly select ciphertexts to decrypt them, taking into account previous results. Theoretically, the capabilities of a cryptanalyst may not be limited to those listed above; Quantitative assessment of the cryptographic strength of encryption algorithms Cryptographic strength is a quantitative characteristic of encryption algorithms - to open a specific encryption algorithm under certain conditions (including a certain cryptanalytic method) requires a certain number of resources. 1. The amount of information required to carry out the attack - say, how many pairs of known or selected texts are needed. 2. The time required to carry out the attack. 3.Memory required to store information used in the attack. The combination of these three values characterizes a specific attack on a specific encryption algorithm. Here and below it is assumed that the encryption algorithm itself is known to the attacker - only the key is unknown. Cryptanalysis of modified algorithms There are many encryption algorithms that are cryptographically strong. 1. An algorithm is cryptographically strong if there are no methods for breaking it, except for the “brute force” method, which will be discussed in the next part of the article. 2. In addition, the key size of the algorithm is large enough to make the brute force method impossible at the current level of computer technology. However, for example, it may be necessary to compare two or more cryptographically strong encryption algorithms (as, for example, in an open competition to select a new US encryption standard, AES). It is known that the vast majority of modern encryption algorithms consist of a certain number of rounds, in each of which the same (or similar) transformations are repeated on the encrypted data. truncated number rounds - i.e. Another option for determining the margin of cryptographic strength is to analyze modifications of the algorithm under study with minor changes in the structure of the round. |
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