计算机英语讲课笔记02

I. The Result of Sign-in

• At the beginning of the class, I will do the sign-in to make sure whether everybody is here (present).
• This time, let’s take a look at the result of the sign-in.
• There are thirty-nine students in our class, but only thirty-seven students have joined my cloud class.
• Thirty-seven students have signed in this time. Another two students joined our cloud class just now.
  

II. Arithmetic Operations

1. Addition

add (v.) $⟹$ addition (n.)$⟹$ additional (adj.)

How to say 37 + 2 = 39 in English?

• Daily English: If you add two to thirty-seven, you will get thirty-nine.
• Math English: Thirty-seven plus two equals thirty-nine.
• Use Python to do the addition
  

2. Subtraction

subtract (v.) $⟹$ subtraction (n.)

How to say 39 - 2 = 37 in English?

• Daily English: If you subtract two from thirty-seven, you will get thirty-seven.
• Math English: Thirty-nineminus two equals thirty-seven.
• Use a Python program to do the subtraction
  
• Life $⟹$ Math $⟹$ Computer (Program $\to$ Software)

3. Multiplication

multiply (v.) $⟹$ multiplication (n.)
multiply (v.) $⟹$ multiple (adj.)
single $⟹$ double $⟹$ multiple

How to say 2 × 3 = 6 in English?

• Daily English: If you multiply two by three, you will get six.
• Math English: Twotimes three equals six.
• Use a Python program to do the multiplication
  

4. Division

divide (v.) $⟹$ division (n.)

How to say 6 ÷ 2 = 3 in English?

• Daily English: If you divide six by two, you will get three.
• Math English: Sixdivided by twoequals two.
• Use a Python program to do the division
  

III. Big Data

Now we are living in the age of big data.

大数据学习笔记：Hadoop生态系统 (Hadoop Ecosystem)

1. Structured Data (SQL DataBase) $⟹$ MySQL, Oracle, SQL Server, DB2 …
2. Non-Structured Data $⟹$ NoSQL (Redis, HBase, MongoDB, …), Text, Picture, Photo, Video, Sound…

Four Types of Keys in Tables

1. Primary Key - id (identity)
2. Candidate Key
3. Unique Key
4. Regular Key
   

IV. Security

1. Three Levels of Security

• Data Security $⟹$ Software Security $⟹$ Network Security
• Personal Security $⟹$ Social Security $⟹$ National Security

2. Two Technologies for Security

1. Authentication 认证 - membership（成员）
2. Authorization 授权 - authority （权限）

V. How to Memorize Words Effectively?

1. Master Word Formation

The most important method for word formation is derivation. 派生是最重要的一种构词法。
Prefix + Root + Suffix

• Nation – national - international - internationalize – internationalization (i18n)

2. Memorize Words Syllable by Syllable

We’d better memorize words syllable by syllable, not letter by letter.

3. Learn Words in Sentences or Articles

• In the sentences or articles we can really learn how to use the words properly. If your really want to enlarge your vocabulary, the best way is not reciting new words but doing extensive reading in various fields, especially reading the materials in which you have real interest.

VI. After-class Reading Materials

Computer Security

The process of ensuring confidentiality, integrity, and availability of computers, their programs, hardware devices, and data. Lack of security results from a failure of one of these three properties. The lack of confidentiality is unauthorized disclosure of data or unauthorized access to a computing system or a program. A failure of integrity results from unauthorized modification of data or damage to a computing system or program. A lack of availability of computing resources results in what is called denial of service.

An act or event that has the potential to cause a failure of computer security is called a threat. Some threats are effectively deflected by countermeasures called controls. Kinds of controls are physical, administrative, logical, cryptographic, legal, and ethical. Threats that are not countered by controls are called vulnerabilities.

1. Encryption

Encryption is a very effective technique for preserving the secrecy of computer data, and in some cases it can also be employed to ensure integrity and availability. An encrypted message is converted to a form presumed unrecognizable to unauthorized individuals. The principal advantage of encryption is that it renders interception useless. See Cryptography

2. Access Control

Computer security implies that access be limited to authorized users. Therefore, techniques are required to control access and to securely identify users. Access controls are typically logical controls designed into the hardware and software of a computing system. Identification is accomplished both under program control and by using physical controls.

Typically, access within a computing system is limited by an access control matrix administered by the operating system or a processing program. All users are represented as subjects by programs executing on behalf of the users; the resources, called the objects of a computing system, consist of files, programs, devices, and other items to which users’ accesses are to be controlled. The matrix specifies for each subject the objects that can be accessed and the kinds of access that are allowed.

Access control as described above relates to individual permissions. Typically, such access is called discretionary access control because the control is applied at the discretion of the object’s owner or someone else with permission. With a second type of access control, called mandatory access control, each object in the system is assigned a sensitivity level, which is a rating of how serious would be the consequences if the object were lost, modified, or disclosed, and each subject is assigned a level of trust.

Access control is not necessarily as direct as just described. Unauthorized access can occur through a covert channel. One process can signal something to another by opening and closing files, creating records, causing a device to be busy, or changing the size of an object. All of these are acceptable actions, and so their use for covert communication is essentially impossible to detect, let alone prevent.

3. Security of Programs

Computer programs are the first line of defense in computer security, since programs provide logical controls. Programs, however, are subject to error, which can affect computer security.

A computer program is correct if it meets the requirements for which it was designed. A program is complete if it meets all requirements. Finally, a program is exact if it performs only those operations specified by requirements.

Simple programmer errors are the cause of most program failures. Fortunately, the quality of software produced under rigorous design and production standards is likely to be quite high. However, a programmer who intends to create a faulty program can do so, in spite of development controls. See Software engineering

A salami attack is a method in which an accounting program reduces some accounts by a small amount, while increasing one other account by the sum of the amounts subtracted. The amount reduced is expected to be insignificant; yet, the net amount summed over all accounts is much larger.

Some programs have intentional trapdoors, additional undocumented entry points. If these trapdoors remain in operational systems, they can be used illicitly by the programmer or discovered accidentally by others.

A Trojan horse is an intentional program error by which a program performs some function in addition to its advertised use. For example, a program that ostensibly produces a formatted listing of stored files may write copies of those files on a second device to which a malicious programmer has access.

A program virus is a particular type of Trojan horse that is self-replicating. In addition to performing some illicit act, the program creates a copy of itself which it then embeds in other, innocent programs. Each time the innocent program is run, the attached virus code is activated as well; the virus can then replicate and spread itself to other, uninfected programs. Trojan horses and viruses can cause serious harm to computing resources, and there is no known feasible countermeasure to halt or even detect their presence.

4. Security of Operating Systems

Operating systems are the heart of computer security enforcement. They perform most access control mediation, most identification and authentication, and most assurance of data and program integrity and continuity of service.

Operating systems structured specifically for security are built in a kernelized manner, embodying the reference monitor concept. A kernelized operating system is designed in layers. The innermost layer provides direct access to the hardware facilities of the computing system and exports very primitive abstract objects to the next layer. Each successive layer builds more complex objects and exports them to the next layer. The reference monitor is effectively a gate between subjects and objects. See Operating system

5. Security of Databases

Integrity is a much more encompassing issue for databases than for general applications programs, because of the shared nature of the data. Integrity has many interpretations, such as assurance that data are not inadvertently overwritten, lost, or scrambled; that data are changed only by authorized individuals; that when authorized individuals change data, they do so correctly; that if several people access data at a time, their uses will not conflict; and that if data are somehow damaged, they can be recovered.

Database systems are especially prone to inference and aggregation. Through inference, a user may be able to derive a sensitive or prohibited piece of information by deduction from nonsensitive results without accessing the sensitive information itself. Aggregation is the ability of two or more separate data items to be more (or less) sensitive together than separately. Various statistical methods make it very difficult to prevent inference, and aggregation is also extremely difficult to prevent, since users can access great volumes of data from a database over long periods of time and then correlate the data independently.

6. Security of Networks

As computing needs expand, users interconnect computers. Network connectivity, however, increases the security risks in computing. Whereas users of one machine are protected by some physical controls, with network access, a user can easily be thousands of miles from the actual computer. Furthermore, message routing may involve many intermediate machines, called hosts, each of which is a possible point where the message can be modified or deleted, or a new message fabricated. A serious threat is the possibility of one machine’s impersonating another on a network in order to be able to intercept communications passing through the impersonated machine.

The principal method for improving security of communications within a network is encryption. Messages can be encrypted link or end-to-end. With link encryption, the message is decrypted at each intermediate host and reencrypted before being transmitted to the next host. End-to-end encryption is applied by the originator of a message and removed only by the ultimate recipient.

To benefit from sharing access to computing systems that are not all located together, organizations have established virtual private networks (VPNs). These networks approach the security of a private network at costs closer to those of shared public resources. The primary security technique used is encryption.

The Internet, or any similar public network, is subject to threats to its availability, integrity, and confidentiality. A complicating feature is that there is effectively no control on transmissions over the Internet. Consequently, a system connected to the Internet is exposed to any malicious attack that any other Internet user wants to launch.

7. Security Perimeter

A security perimeter is a logical boundary surrounding all resources that are controlled and protected. The protected resources are called a domain (or enclave or protected subnetwork). There may be overlapping domains of varying protection, so that the most sensitive resources are in the innermost domain, which is the best protected. Protecting the security perimeter may be physical controls, identification and authentication, encryption, and other forms of access control. Two controls that relate especially to the security perimeter are network vulnerability scanning and firewalls.

A network vulnerability scan is the process of determining the connectivity of the subnetwork within a security perimeter, and then testing the strength of protection at all the access points to the subnetwork. With a network domain, if a forgotten access point is not secured, its weakness can undermine the protection of the rest of the domain. A network scanner maps the connectivity of a domain, typically by probing from outside the domain, to determine what resources are visible from the outside. Once all outside connections are identified, each is tested with a range of attacks to determine the vulnerabilities to which it is susceptible and from which it needs to be better protected.

A firewall is a host that fuctions as a secured gateway between a protected enclave and the outside. The firewall controls all traffic according to a predefined access policy. For example, many firewalls are configured to allow unhindered communication outbound (from the protected domain to a destination outside the domain) but to allow only certain kinds of inbound communication. A firewall can be a separate computer, or firewall functionality can be built into the communications switch connecting the enclave to the external network.

8. Intrusion Detection

It is most effective to eliminate vulnerabilities, but if that is not possible, it is then desirable to recognize that an attack is occuring or has occured, and take action to prevent future attacks or limit the damage from the current one. Intrusion detection can be either anomaly detection, which seeks to identify an attack by behavior that is out of the norm, or misuse detection, to identify an attack by its attempted effect on sensitive resources. Intrusion detection systems monitor a computing system in order to warn of an attack that is imminent, is under way, or has occurred.

Password Security

USER IDS, passwords, and personal identification numbers (PINs) are a fact of everyday life in the information age. They are required for activities such as using ATMs and debit cards, logging into Windows, accessing wireless networks, making an iTunes purchase, instant messaging, reading
e-mail, and file sharing. Many Web sites encourage you to sign up for membership by choosing a user ID and password. This section provides information about selecting secure passwords and managing the mountain of passwords you collect and tend to forget.

AUTHENTICATION PROTOCOLS

What is an authentication protocol?

Security experts use the term authentication protocol to refer to any method that confirms a person’s
identity using something the person knows, something the person possesses, or something the person is. For example, a person might know a password or PIN. A person might possess an ATM card or a credit card. A person can also be identified by biometrics, such as a fingerprint, facial features (photo), or retinal pattern.

Authentication protocols that use more than one means of identification are more secure than others. Two-factor authentication, which verifies identity using two independent elements of confirmation such as an ATM card and PIN, is more secure than single-factor authentication, such as a password.
Computer-related security is primarily based on passwords associated with user IDs. The level of protection offered by single-factor authentication depends on good password selection and management on the part of users.

What is a user ID?

A user ID is a series of characters—letters and possibly numbers or special symbols—that becomes a person’s unique identifier, similar to a Social Security number. It is also referred to as a username, login, screenname, online nickname, or handle. User IDs are typically public. Because they are not secret, they do not offer any level of security.

User IDs are significant because they are the name on an account, such as e-mail or iTunes, that requires a password. When you first apply for or set up an account, you might be supplied with a user ID or you might be asked to create one. Often a user ID is a variation of your name. Brunhilde Jefferson’s user ID might be bjeffe, bjefferson, brunhilde_jefferson, or bjeff0918445. It is also becoming common to use your e-mail address as a user ID.

The rules for creating a user ID are not consistent throughout all applications, so it is important to read instructions carefully before finalizing your user ID. For example, spaces might not be allowed in a user ID. Hence, the underline in brunhilde_jefferson is used instead of a space. There might be a length limitation, so Ms. Jefferson might have to choose a short user ID, such as bjeffe.

Some computers that host password-protected resources don’t differentiate between uppercase and lowercase letters, and would consider the user IDs B_Jefferson and b_jefferson to be the same. Other computers are case sensitive and differentiate between uppercase and lowercase. On such computers, if Ms. Jefferson selected Brun_Jeff as her user ID, she would not be able to gain access by typing brun_jeff. To avoid such problems, most people stick to lowercase letters for their user IDs.

What is a password?

A password is a series of characters that verifies a user ID and guarantees that you are the person you claim to be. Although you might be assigned a password, typically you are asked to provide your own. In some situations you might be given a temporary password, and then asked to change it as soon as you successfully log in for the first time. Passwords and user IDs are typically created on a registration or enrollment screen similar to the one in the following figure.

What if I forget my password?

Login screens for many applications provide a “forgot my password” link. Clicking this link checks your identity using your answer to a personal question. If your identity checks out, your password is e-mailed to you. A personal question provides an alternative authentication protocol to ensure that you are not a hacker pretending to have lost a password.

Personal questions and answers are usually set up at the same time you create an account. After selecting a password, you are required to choose a question that you must answer before your forgotten password is e-mailed to you. This question might be something like: What is your
mother’s maiden name?, What is your favorite color?, or Where were you born? You should be careful about the question you choose because public information like your mother’s maiden name or the town of your birth can be researched by any hacker.

What is the difference between a password and a PIN?

Both passwords and PINs are classified as something-the-user-knows authentication methods. In practice, PINs tend to be a sort sequence of numbers that can be entered using a numeric keypad, whereas passwords tend to be longer sequences of letters, numbers, and special characters that
require a full qwerty keyboard for entry. PINs are typically used with twofactor authentication protocols, whereas passwords are used in conjunction with single-factor authentication protocols.

For example, ATMs require a bank card (something you possess) and a PIN (something you know). In contrast, passwords are associated with single-factor authentication used for networks, Web sites, and other situations in which the hardware for dealing with ID cards is not available.

PASSWORD HACKS

SECURE PASSWORDS