The blockchain brother community, the pioneer of blockchain technology professional Q&A, the gathering place for Chinese blockchain technology enthusiasts
Author: Yu Zhongyang
Source: Blockchain Brothers
Original link: http://www.blockchainbrother.com/article/72
Copyright belongs to the author. For commercial reprints, please contact the author for authorization, and for non-commercial reprints, please indicate the source.
1. Sender and Receiver
The sender (sender) is the person who sends the information message, and it wants to send the message to the receiver (receiver), and the receiver is the person who receives the information message. During the sending process, both the sender and the legitimate receiver want to send and receive the information message securely, and need to be sure that a third party (eavesdropper) cannot intercept or read the sent information message.
2. Messaging and Encryption
The message (message) is the plaintext (plaintext). The process of "camouflaging" it in a specific way to hide its content is called encryption. The encrypted message is called ciphertext. When we convert ciphertext into plaintext, we call this process decryption.
This process is simply: "plaintext" >> (encryption) >> "ciphertext" >> (decryption) >> "original plaintext".
In the process, the technique of keeping messages secret is called cryptography, and the people who do it are called cryptographers. The opposite of this is the technology of deciphering ciphertext, which we call cryptanalysis, and the people who do this work are professionals who analyze and process passwords, which we call cryptanalyst.
Cryptology (cryptology) includes two parts of cryptography and cryptanalysis, so people who are good at both are called cryptologists. Since cryptography is a branch of mathematics, modern cryptographers are usually also theoretical mathematicians.
Note: Cryptography and mathematics are inextricably linked. Learning cryptography also requires learning mathematics.
The plaintext is generally represented by M or P, and the plaintext can be a bit sequence, a bitmap, a text file, a digitized speech sequence, or a digitized video image, and so on. For computers, M generally simply refers to binary data. Plaintext may be transmitted or stored, in which case M refers to the information message to be encrypted.
The ciphertext is represented by C, which is also binary data, sometimes as large as M, sometimes larger than M, but through the combination of compression and encryption, C may also be smaller than M. Now I assume that the encryption function is E, then the process of E acting on M to get C can be expressed by mathematical formulas:
E(M)=C
Conversely, if the decryption function is assumed to be D, the process of the decryption function D acting on C to generate M can be expressed as:
D(C)=M
The encryption operation is performed first, followed by the decryption operation, and the original plaintext will be recovered, so the following equation is established:
D( E(M) )=M
3. The role of cryptography
The usual role of cryptography is to provide confidentiality, but beyond that, cryptography has the following roles.
Authentication (authentication) The receiver of the message should be able to confirm the source of the message, and it is impossible for a third-party intruder to pretend to be the legitimate sender and receiver.
The receiver of the integrity information message should be able to verify that the information message has not been tampered with during the transmission process, and it is impossible for a third-party intruder to replace the legitimate information message with a false information message.
The sender of a non-repudiation information message cannot unilaterally and falsely deny that it sent the information message afterwards.