The Advanced Encryption Standard that will replace DES (the Data Encryption Standard) around the turn of the century.

The traditional method of modulating radio signals so that they can carry information. Amplitude modulation (AM) and frequency modulation (FM) are the two most common methods of analog modulation. Today, most U.S. cellular systems carry phone conversations using analog; the transition to digital transmissions is happening slowly.

Applet is a diminutive form of app (application), and it refers to simple, single-function programs that often ship with a larger product. Programs such as Windows' Calculator, File Manager, and Notepad are examples of applets. It can also refer to little Java programs that run on web pages.

American Standard Code for Information Interchange. Bland, unformatted text files are best saved in ASCII (pronounced "askee") format. But ASCII is more than a text file format--it's a standard developed by the American National Standards Institute (ANSI) to define how computers write and read characters. The ASCII set of 128 characters includes letters, numbers, punctuation, and control codes (such as a character that marks the end of a line). Each letter or other character is represented by a number: an uppercase A, for example, is the number 65, and a lowercase z is the number 122. Most operating systems use the ASCII standard, except for Windows NT, which uses the suitably larger and newer Unicode standard.

In a general sense, this term describes information-carrying capacity. It can apply to telephone or network wiring as well as system buses, radio frequency signals, and monitors. Bandwidth is most accurately measured in cycles per second, or hertz (Hz), which is the difference between the lowest and highest frequencies transmitted. But it's also common to use bits or bytes per second instead.
Caches come in many types, but they all work the same way: they store information where you can get to it fast. A Web browser cache stores the pages, graphics, sounds, and URLs of online places you visit on your hard drive; that way, when you go back to the page, everything doesn't have to be downloaded all over again. Since disk access is much faster than Internet access, this speeds things up.

As the name implies, codecs are used to encode and decode (or compress and decompress) various types of data--particularly those that would otherwise use up inordinate amounts of disk space, such as sound and video files. See, for example, MP3.

Cookies are small data files written to your hard drive by some Web sites when you view them in your browser. These data files contain information the site can use to track such things as passwords, lists of pages you've visited, and the date when you last looked at a certain page.

The dividing lines between what is and what is not cryptography have become blurred. But to most people, and for purposes of this class, cryptography is concerned with keeping communications private, i.e. guarding the electronic transfer of your Visa number from peeping Toms on the Internet.

Cybersquatting describes the potentially lucrative process of registering popular trademark names or names sufficiently similar to a trademark as Internet domain names, then selling them for outrageous fees to companies who hold the trademarks.


Data mining is the process of discovering new correlations, patterns and trends by sifting through large amounts of data stored in repositories or databases and using pattern recognition technologies as well as statistical and mathematical techniques. Data mining can be a goldmine for any business that wants to improve its bottom line by tracking consumer behavior in new and efficient ways. It is also essential to fields that depend on substantive research, such as healthcare. Along with data mining, however, come privacy concerns: how are miners acquiring their data, i.e. through cookies, how is it being used, and when does their use of your data put you at risk?

Data Encryption Standard, an encryption method developed by IBM and the U.S. government in the 1970's as an official standard.

In an attempt to assuage fears of online transactions, software vendors, security specialists, and online vendors have developed the concept of digital certificates. A digital certificate is a password-protected file that includes a variety of information: the name and email address of the certificate holder, an encryption key that can be used to verify the digital signature of the holder, the name of the company issuing the certificate, and the period during which the certificate is valid. Certificate authorities (CAs) gather information about a person or company and then issue certificates. These certificates can be used as online identification, much in the same way a driver's license can verify your identity in the physical world.

Digital signatures are a means of proving that a file or email message belongs to a specific person, much as a driver's license proves identity in real life. Digital signatures have the added benefit of verifying that your message has not been tampered with. When you sign a message, a hash function--a computation that leaves a specific code, or "digital fingerprint"--is applied to it. If the fingerprint on the recipient's message doesn't match the original fingerprint, the message has been altered.

You'll find them to the right of the @ sign in an email address, or about ten characters into a URL. HLS's domain name is law.harvard.edu. See TLDs, Cybersquatting.


Encryption is the process of changing data into a form that can be read only by the intended receiver. To decipher the message, the receiver of the encrypted data must have the proper decryption key. In traditional encryption schemes, the sender and the receiver use the same key to encrypt and decrypt data. Public-key encryption schemes use two keys: a public key, which anyone may use, and a corresponding private key, which is possessed only by the person who created it.

Ethernet is a standard for connecting computers into a local area network (LAN). The most common form of Ethernet is called 10BaseT, which denotes a peak transmission speed of 10 mbps using copper twisted-pair cable.

Also known as rules, filters can be used to censor Internet content or to manage incoming and stored mail. Software that supports filters lets you create rules that perform actions, such as preventing a particular Internet user from accessing a prohibited site or automatically routing messages to various folders based on the sender's address. See, for example, PICS.

If you want to protect any networked server from damage (intentional or otherwise) by those who log in to it, you put up a firewall. This could be a dedicated computer equipped with security measures such as a dial-back feature, or it could be software-based protection called defensive coding.

A hash function takes a variable sized input and has a fixed size output. What this means in plain English is that the hash is used to authenticate an email or document by leaving a specific piece of code on it, such that the document has a "digital fingerprint" that would signal tampering.

Hypertext Markup Language. As its name suggests, HTML is a collection of formatting commands that create hypertext documents--Web pages, to be exact. When you point your Web browser to a URL, the browser interprets the HTML commands embedded in the page and uses them to format the page's text and graphic elements. HTML commands cover many types of text formatting (bold and italic text, lists, headline fonts in various sizes, and so on), and also have the ability to include graphics and other nontext elements.

This address is a unique string of numbers that identifies a computer on the Internet. These numbers are usually shown in groups separated by periods, like this: All resources on the Internet must have an IP address--or else they're not on the Internet at all.

Integrated Services Digital Network. The plain old telephone system doesn't handle large quantities of data, and the phone companies realized this a long time ago. So the ISDN spec was hammered out in 1984 to allow for wide-bandwidth digital transmission using the public switched telephone network. Under ISDN, a phone call can transfer 64 kilobits of digital data per second. But it's not always easy to adopt.

Internet Service Provider. Once upon a time, you could only connect to the Internet if you belonged to a major university or had a note from the Pentagon. Not anymore: ISPs have arrived to act as your (ideally) user-friendly front end to all that the Internet offers. Most ISPs have a network of servers (mail, news, Web, and the like), routers, and modems attached to a permanent, high-speed Internet "backbone" connection. Subscribers can then dial into the local network to gain Internet access--without having to maintain servers, file for domain names, or learn Unix.

Sun Microsystems' Java is a programming language for adding animation and other action to Web sites. The small applications (called applets) that Java creates can play back on any graphical system that's Web-ready, but your Web browser has to be Java-capable for you to see it.

Used widely in cryptography, keys are like pieces of code that allow you to encrypt and decrypt data. Incidentally, a key can be used to perform other mathematical operations as well.

Local area network. A local area network is a short-distance network used to link a group of computers together within a building. 10BaseT Ethernet is the most commonly used form of LAN. A piece of hardware called a hub serves as the common wiring point, enabling data to be sent from one machine to another over the network. LANs are typically limited to distances of less than 500 meters and provide low-cost, high-bandwidth networking capabilities within a small geographical area.

These pieces of HTML are embedded into the heading sections of an HTML web page and are invisible to surfers. They are designed to help classify a web page for search engines, etc. but are now used to stuff lots of terms into a web page that may make it more visible to a web surfer. For example, we could stuff our IS99 web page with invisible and irrelevant meta tags such as "Bill Clinton" so that whenever a person does a search on Bill Clinton, our page will come up in the search results.

MPEG-1, Layer 3. MP3 is a codec that compresses standard audio tracks into much smaller sizes without significantly compromising sound quality. The rise of MP3 has generated a highly publicized debate concerning the distribution and protection of music over the Internet.

Moving Pictures Experts Group. MPEG is a standard for compressing sound and movie files into an attractive format for downloading--or even streaming--across the Internet. The MPEG-1 standard streams video and sound data at 150 kilobytes per second--the same rate as a single-speed CD-ROM drive--which it manages by taking key frames of video and filling only the areas that change between the frames. Unfortunately, MPEG-1 produces only adequate quality video, far below that of standard TV. MPEG-2 compression improves things dramatically. With MPEG-2, a properly compressed video can be shown at near-laserdisc clarity with a CD-quality stereo soundtrack. For that reason, modern video delivery mediums, such as digital satellite services and DVD, use MPEG-2.

Citizens of the Internet. If you were not a netizen by this fall, you will certainly become one during this course.

Platform for Privacy Preference Project. The P3P project, activity, products, and specifications seek to enable Web sites to express their privacy practices and enable users to exercise preferences over those practices. P3P products will act as an initial privacy-screening device and attempt to address the current privacy concerns that plague both Internet surfers and webmasters. Users will be informed of site practices, will be able to delegate decisions to their computer when appropriate, and will be able to tailor their relationship to specific sites vis a vis privacy preferences.

Platform for Internet Content Selection. PICS is a filtering scheme that allows content providers and independent organizations to publish their own content-based label for any URL. Both content providers and third party users may choose which rating system to use.

Computers can't just throw data at each other any old way. Because so many different types of computers and operating systems connect via modems or other connections, they have to follow communications rules called protocols. The Internet is a very heterogenous collection of networked computers and is full of protocols.

A proxy server is a system that caches items from other servers to speed up access. On the Web, a proxy first attempts to find data locally, and if it's not there, fetches it from the remote server where the data resides permanently.

In public key cryptography, each person gets a pair of keys, one called the public key and the other called the private key. The public key is published, while the private key is kept secret. There is no need for the sender and receiver to share secret information; all communications involve only public keys, and no private key is ever transmitted or shared. See Secret Key Cryptography. Therefore, you don't have to worry about whether the communications channels transmitting your encrypted message are sufficiently secure. The only requirement is that public keys be associated with their users in a trusted (authenticated) manner. Anyone can send a confidential message by just using public information, but the message can only be decrypted with a private key, which is in the sole possession of the intended recipient.

Secure Digital Music Initiative. An attempt to create an alternative to MP3 that would allow companies to track copyrights and be secure in the knowledge that a user could not remove that copyright information. See sdmi.org.

Secret key is the traditional method of encryption and decryption. In secret key, or "symmetric key", the sender and receiver of a message know and use the same secret key: the sender uses the secret key to encrypt the message, and the receiver uses the same secret key to decrypt the message. The main challenge, however, is getting the sender and receiver to agree on the secret key without anyone else finding out. Because all keys in a secret key system must remain secret, secret-key cryptography often has difficulty providing secure key management, especially in open systems with a large number of users. See public key cryptography.

The business end of a client/server setup, a server is usually a computer that provides the information, files, Web pages, and other services to the client that logs on to it. (The word server is also used to describe the software and operating system designed to run server hardware.) The client/server setup is analogous to a restaurant with waiters and customers. Some Internet servers take this analogy to extremes and become inattentive, or even refuse to serve you.

Spiced Ham. Hormel's famous can o' additives has given its name to something almost as disgusting: junk email. Spam can be a mass mailing to bulletin boards, newsgroups, or lists of people. But spam is never welcome: if you spam or get spammed, flame wars can ensue.

Also known as a Web spider, this class of robot software explores the World Wide Web by retrieving a document and following all the hyperlinks in it. Web sites tend to be so well linked that a spider can cover vast amounts of the Internet by starting from just a few sites. After following the links, spiders generate catalogs that can be accessed by search engines. Popular search sites like Alta Vista, Excite, and Lycos use this method.

Data is streaming when it's moving quickly from one chunk of hardware to another and doesn't have to be all in one place for the destination device to do something with it. When your hard disk's data is being written to a tape backup device, it's streaming. When you're watching a QuickTime movie on the Internet, it's not streaming, because the movie must be fully downloaded before you can play it.

Top Level Domains. TLDs refer to the last extension on a domain name , like. "edu" or "com" or "mil". In a hierarchical classification system, TLD's fill the highest, or most generalized, level of classification; currently, there are about 260 of them (most of them country extensions like .uk or .fr). Their future -- particularly who owns the right to assign and create new TLDs -- is the subject of much contention and, not surprisingly, our first two classes.

Unix took off in the early 1970s as a general-purpose operating system. Since much of the Internet is hosted on Unix machines, the operating system took on a new surge of popularity in the early 1990s. Unix comes in many flavors--including Xenix, Ultrix, GNU, and Linux--and runs on a variety of platforms, which makes its development a subject of widespread discussion.

Usenet is a worldwide network of thousands of Unix systems with a decentralized administration. The Usenet systems exist to transmit postings to special-interest newsgroups covering just about any topic you can imagine (and many you wouldn't even want to imagine).

Wares is short for software or hardware.

The World Intellectual Property Organization, located in Geneva, Switzerland.

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