计算子专业英语第八章.ppt

Passage D Encryption 1. ?What is encryption? Encryption is a way to send a message in code(Figure 8-6). The original message is called plaintext?(明文). The only person who can decode?(解码) the message is the person with the correct key; to anyone else, the message looks like a random series of letters, numbers, and characters, is called ciphertext (密文).[1] In other words, data encryption is the process of scrambling?(不规则的) stored or transmitted information so that it is unintelligible?(无法理解的) until it is unscrambled by the intended recipient?(接受者). All modern cryptography is based on the use of algorithms?(算法). The operation of the algorithm requires the use of a key. Figure 8-6 Encryption and decryption 2. ?When encryption is used? Historically, data encryption has been used primarily to protect diplomatic?(外交的) and military secrets from foreign governments. It is also now used increasingly by the financial industry to protect money transfers, by merchants to protect credit-card information in electronic commerce, and by corporations to secure sensitive communications of proprietary?(私有的) information.[2] Computer encryption is based on the science of cryptography?(密码学). 3. ?Two Types of Encryption There are two main types of encryption: symmetric?(对称的) key encryption and asymmetric?(非对称的) encryption，also called public key (公钥)?encryption. With symmetric key encryption, the same “key” is used to encrypt and decrypt?(解密) a message.? An encryption “key” is simply a string of letters, digits or symbols which are used to encode or decode a message. To use public key encryption, you must first generate a key pair, which are two very large numbers that are mathematically related to each other. [3]One of these keys is your private key and one is your public key. When someone wants to send you a secret message, they use your public key to encrypt it. You are then able to use your private key to decrypt it. As you can see , your public