Basics

• Symmetric cryptosystem: also known as private-key encryption/decryption, in which the same key is used to cipher (by the sender) and decipher (by the receiver) data

• Public-key cryptosystem: also known as asymmetric encryption/decryption. It uses a pair of keys: a public key and a private key, with each used for encryption/decryption. For example, if the public key is used to encrypt a message, the private key will be used to decrypt the message.

• Hybrid cryptosystem: It combines the efficiency of a symmetric cryptosystem with the convenience of a public-key cryptosystem. Symmetric cryptosystem boosts the efficiency of encryption and decryption, and public-key cryptosystem helps distribute keys.

• Digital digest: Turns messages at different lengths into short messages at a certain length, often used with one-way hash function.

• Message authentication code (MAC): a message authentication mechanism which not only examines whether a message is tampered with, but also checks whether a message comes from an expected communication object

Digital signature: The strings, which can only be generated by the message sender and cannot be fabricated by other parties, can be used as valid credentials for the authenticity of a sent message. Compared with MAC, digital signature stands out for its non-repudiation.