- [讲师]在我们开始深入研究密码学的细节之前 您需要了解更多术语 zwsub.com中文字幕网 全套Lynda/Pluralsight教程附带中英文字幕 - [Instructor] There's a little more terminology that you'll need to know before we start diving in to the details of cryptography.
我们来谈谈代码和密码 zwsub.com中文字幕网 全套Lynda/Pluralsight教程附带中英文字幕 Let's talk about codes, and ciphers.
代码和密码是不同的概念 zwsub.com中文字幕网 全套Lynda/Pluralsight教程附带中英文字幕 Codes and ciphers are different concepts.
人们经常互换使用这些术语 但它们实际上是两个非常不同的东西 People often use these terms interchangeably, but they are actually two very different things.
您需要确保在参加考试时了解代码和密码之间的区别 You need to be sure that you understand the difference between codes and ciphers when you take the exam.
代码是将一个有意义的单词或短语替换为另一个的系统 A code is a system that substitutes one meaningful word or phrase for another.
这可能是出于保密目的而做的 或者可能是为了提高通信效率 允许短消息传达详细的含义 This might be done for secrecy purposes, or it might be done for efficiency of communications, allowing a short message to convey a detailed meaning.
您可能已经听说过的代码的一个示例是警察和其他通过无线电通信的组织使用的Ten Code系统 One example of a code that you've probably already heard of is the Ten Code system, used by police, and other organizations who communicate by radio.
他们有很长的代码列表 允许发送消息的人简单地说两个数字 并传达一个很长的意义 They have a long list of codes, that allow the person sending a message to simply say two numbers, and convey a long meaning.
例如 10-4表示“我确认您的消息” 10-9表示“请重复上一次传输” 这是使用代码来提高通信效率的示例 For example, 10-4 means "I acknowledge your message." While 10-9 means "Please repeat your last transmission." This is an example of using codes for the efficiency of communication.
您还会在间谍电影中看到常常弹出的代码 You'll also see codes pop up often in spy movies.
当一名秘密行动人员从现场打电话说：“蓝牛跳过月球” 但实际上意味着监视行动的主题消失了 When a secret operative calls in from the field and says, "The blue cow jumped over the moon", but really means that the subject of a surveillance operation disappeared.
这是使用代码保密的一个例子 That's an example of using codes for secrecy.
另一方面 密码是使用数学算法来加密和解密消息的系统 Ciphers, on the other hand, are systems that use mathematical algorithms to encrypt and decrypt messages.
我们在本课程中讨论的所有加密算法都是密码的示例 而不是代码 All of the cryptographic algorithms we talk about in this course are examples of ciphers, not codes.
密码有两种不同的处理消息的方式 Ciphers have two different ways of processing a message.
流密码一次处理消息的一个字符 Stream ciphers work on one character of the message at a time.
它们对单个字符或单个位执行操作 然后继续执行下一个字符或位 They perform their action on a single character, or a single bit, and then move on to the next character or bit.
分组密码同时处理消息的块 称为块 Block ciphers work on chunks of the message, known as blocks, at the same time.
例如 它们可能需要100个字符的消息 并同时对它们进行加密 They might take 100 characters of a message, for example, and encrypt them all at the same time.
密码使用两个基本构建块执行加密和解密操作 Ciphers perform their encryption and decryption operations using two basic building blocks.
替换密码实际上会更改消息中的字符 Substitution ciphers actually change the characters in a message.
例如 一个简单的替换密码可能会将消息中的所有字母移动两个位置 将A改为C 将B改为D 依此类推 A simple substitution cipher might, for example, shift all of the letters in a message by two positions, changing the A's to C's, the B's to D's, and so on.
当有人想要解密消息时 他们只需将字符移回两个位置即可 When someone wants to decrypt the message, they simply shift the characters back by two positions.
换位密码不会更改消息中的字符 而是重新排列它们 Transposition ciphers don't change the characters in a message, but instead they rearrange them.
它们基本上是在加扰消息 只有知道解密密钥的人才能解密它们 They're basically scrambling up the message in a way that only someone who knows the decryption key can unscramble them.
我们刚刚讨论了替换和转置密码的两个非常基本的例子 We just talked about two very basic examples of substitution and transposition ciphers.
你今天不会使用它们 因为它们很容易破解 但这两个操作确实形成了现代加密算法的基础 我们将在本课程后面讨论 You wouldn't use these today, because they're very easy to crack, but these two operations do form the basis of the modern encryption algorithms that we'll talk about later in this course.