求教：“计算机英语”书上的两句翻译，关于密码和加密的

原文：
Cryptographic systems can be deivide into two categories: a symmetric key cryptosystem where the key information is shared and kept secret between the sender and receiver, and a public key cryptiosystem where the sender and the receiver do not share the same key (one can be made public while the other is kept secret). Both symmetric key and public key cryptosystem provide security services such as confidentiality, authentication of data source, and integrity. These are achieved through a variety of techniques, namely, message authentication code and hash functions in symmetric key cryptosystems and the use of public and private key in public key cryptosystems.

明天考试了，请帮帮忙吧，谢过了。

求教：“计算机英语”书上的两句翻译，关于密码和加密的 翻译两句计算机英语,不难的 两句英语的回答~~ 两句英语的翻译 求教一句英语语句的解释 求教，《白头吟》里最后两句的意思？？ 请教两句英语的正误 翻译两句简单的英语 谢谢 两句有点专业的英语看不懂 翻译两句简单的英语