What encryption algorithms are there in computer cryptography?

Cryptography is an ancient and profound subject, which ordinary people are not familiar with, because for a long time, it has only been applied in a few fields, such as military, diplomatic and intelligence departments. Computer cryptography is a science that studies the encryption, decryption and transformation of computer information. It is an interdisciplinary subject of mathematics and computer, and it is also a new subject. With the development of computer network and computer communication technology, computer cryptography has received unprecedented attention, and has been rapidly popularized and developed. Abroad, it has become the main research direction of computer security and the main content of computer security course teaching.

Password is the main means to realize secret communication, and it is a special symbol to hide language, words and images. Any communication method that uses special symbols to hide the message prototype according to the agreed method of both parties and is not recognized by the third party is called cryptographic communication. In computer communication, information is hidden by cryptographic technology, and then the hidden information is transmitted, so that even if the information is stolen or captured in the transmission process, the thief cannot know the content of the information, thus ensuring the security of information transmission.

Any encryption system includes at least the following four components:

(1), an unencrypted message, also known as plaintext.

(2) Encrypted messages, also called ciphertext.

(3), encryption and decryption equipment or algorithm.

(4) Encryption and decryption keys.

The sender encrypts the information with an encryption key and sends it out through an encryption device or algorithm. After receiving the ciphertext, the receiver decrypts the ciphertext with the decryption key and restores it to plaintext. If someone steals it in transmission, they can only get incomprehensible ciphertext, thus keeping the information confidential.

Second, the classification of passwords.

According to different standards from different angles, passwords can be divided into several categories.

(a) according to the application technology or historical development stage:

1, manual password. A password encrypted manually or with the assistance of a simple device is called a manual password. This was the main form of combat before the First World War.

2. Mechanical password. A password that uses a mechanical cipher machine or an electronic cipher machine to complete encryption and decryption operations is called a mechanical cipher. From the appearance of World War I to World War II, this password was widely used. 3. Electronic civil strife password. Through electronic circuits, logical operations are carried out with strict procedures, and a large number of encrypted random numbers are generated with a small number of scrambling elements. Because scrambling is completed in the process of encryption and decryption, it does not need to be made in advance, so it is called the civil strife password of electronic computer. From the late 1950s to 1970s, it was widely used.

4, computer password, characterized by computer software programming algorithm encryption, suitable for computer data protection and network communication and other widely used passwords.

(2) According to the degree of confidentiality:

1, theoretical secret password. No matter how many ciphertexts you get and how much computing power you have, a password that can never get the unique solution of plaintext is called a theoretical secret password. Also known as the theoretically unbreakable password. For example, an objective random password with one secret at a time falls into this category.

2. It is actually a secret password. A password that can be cracked theoretically, but cannot be determined by calculation under the existing objective conditions, is called a secret password.

3. Unsafe password. A password that can get a unique solution after obtaining a certain amount of ciphertext is called an unsafe password. For example, early passwords were replaced by a single table, later passwords were replaced by multiple tables, and there were passwords with a small number of keys in plain text. These passwords are not confidential.

(3), key mode:

1, symmetric password. Passwords in which the sender and the receiver use the same key are called symmetric passwords. Traditional passwords all fall into this category.

2. Asymmetric password. Passwords in which the sender and the receiver use different keys are called asymmetric passwords. For example, public key cryptography in modern cryptography belongs to this category.

(four) according to the clear form:

1, analog password. Used to encrypt analog information. For example, a password that encrypts a voice signal that changes constantly in a dynamic range is called an analog password.

2. Digital password. Used to encrypt digital information. A cipher that encrypts telegraph information with the binary relation 0, 1 between two discrete levels is called a digital cipher.

(5) According to the compilation principle:

It can be divided into three types: substitution, substitution and substitution, and their combined forms. Passwords, no matter how complicated and ingenious, are compiled according to these three basic principles. The three principles of shift, substitution and permutation are combined with each other and used flexibly in the compilation and use of passwords.