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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"><HTML><HEAD> <TITLE>Maximum Security -- Ch 7 -- Birth of a Network: The Internet</TITLE></HEAD><BODY TEXT="#000000" BGCOLOR="#FFFFFF"><CENTER><H1><IMG SRC="../button/samsnet.gif" WIDTH="171" HEIGHT="66" ALIGN="BOTTOM" BORDER="0"><BR><FONT COLOR="#000077">Maximum Security: </FONT></H1></CENTER><CENTER><H2><FONT COLOR="#000077">A Hacker's Guide to Protecting Your Internet Site and Network</FONT></H2></CENTER><CENTER><P><A HREF="../ch06/ch06.htm"><IMG SRC="../button/previous.gif" WIDTH="128" HEIGHT="28"ALIGN="BOTTOM" ALT="Previous chapter" BORDER="0"></A><A HREF="../ch08/ch08.htm"><IMGSRC="../button/next.gif" WIDTH="128" HEIGHT="28" ALIGN="BOTTOM" ALT="Next chapter"BORDER="0"></A><A HREF="../index.htm"><IMG SRC="../button/contents.gif" WIDTH="128"HEIGHT="28" ALIGN="BOTTOM" ALT="Contents" BORDER="0"></A> <HR></CENTER><CENTER><H1><FONT COLOR="#000077">7</FONT></H1></CENTER><CENTER><H1><FONT COLOR="#000077">Birth of a Network: The Internet</FONT></H1></CENTER><P>Readers already familiar with the Internet's early development may wish to bypassthis little slice of history. The story has been told many times.</P><P>Our setting is the early 1960s: 1962, to be exact. Jack Kennedy was in the WhiteHouse, the Beatles had just recorded their first hit single (<I>Love Me Do</I>),and Christa Speck, a knock-out brunette from Germany, made Playmate of the Year.Most Americans were enjoying an era of prosperity. Elsewhere, however, Communismwas spreading, and with it came weapons of terrible destruction.</P><P>In anticipation of impending atomic disaster, The United States Air Force chargeda small group of researchers with a formidable task: creating a communication networkthat could survive a nuclear attack. Their concept was revolutionary: a network thathad no centralized control. If 1 (or 10, or 100) of its nodes were destroyed, thesystem would continue to run. In essence, this network (designed exclusively formilitary use) would survive the apocalypse itself (even if we didn't).</P><P>The individual largely responsible for the creation of the Internet is Paul Baran.In 1962, Baran worked at RAND Corporation, the think tank charged with developingthis concept. Baran's vision involved a network constructed much like a fishnet.In his now-famous memorandum titled <I>On Distributed Communications: I. Introductionto Distributed Communications Network</I>, Baran explained:<DL> <DD>The centralized network is obviously vulnerable as destruction of a single central node destroys communication between the end stations. In practice, a mixture of star and mesh components is used to form communications networks. Such a network is sometimes called a `decentralized' network, because complete reliance upon a single point is not always required.</DL><BLOCKQUOTE> <P><HR><FONT COLOR="#000077"><B>Cross Reference:</B></FONT><B> </B>The RAND Corporation has generously made this memorandum and the report delivered by Baran available via the World Wide Web. The documents can be found at <A HREF="http://www.rand.org/publications/electronic/"><B>http://www.rand.org/publications/electronic/</B></A>. <HR></BLOCKQUOTE><P>Baran's model was complex. His presentation covered every aspect of the proposednetwork, including routing conventions. For example, data would travel along thenetwork by whatever channels were available at that precise moment. In essence, thedata would dynamically determine its own path at each step of the journey. If itencountered some sort of problem at one crossroads of the Net, the data would findan alternate route. Baran's proposed design provided for all sorts of contingencies.For instance, a network node would only accept a message if that node had adequatespace available to store it. Equally, if a data message determined that all nodeswere currently unavailable (the <I>all lines busy</I> scenario), the message wouldwait at the current node until a data path became available. In this way, the networkwould provide intelligent data transport. Baran also detailed other aspects of thenetwork, including</P><UL> <LI><FONT COLOR="#000000">Security<BR> <BR> </FONT> <LI><FONT COLOR="#000000">Priority schemes (and devices to avoid network overload)<BR> <BR> </FONT> <LI><FONT COLOR="#000000">Hardware<BR> <BR> </FONT> <LI><FONT COLOR="#000000">Cost</FONT></UL><PRE></PRE><P>In essence, Baran eloquently articulated the birth of a network in painstakingdetail. Unfortunately, however, his ideas were ahead of their time. The Pentagonhad little faith in such radical concepts. Baran delivered to defense officials an11-volume report that was promptly shelved.</P><P>The Pentagon's shortsightedness delayed the birth of the Internet, but not bymuch. By 1965, the push was on again. Funding was allocated for the development ofa decentralized computer network, and in 1969, that network became a reality. Thatsystem was called <I>ARPANET</I>.</P><P>As networks go, ARPANET was pretty basic, not even closely resembling the Internetof today. Its topology consisted of links between machines at four academic institutions(Stanford Research Institute, the University of Utah, the University of Californiaat Los Angeles, and the University of California at Santa Barbara).</P><P>One of those machines was a DEC PDP-10. Only those more mature readers will rememberthis model. These are massive, ancient beasts, now more useful as furniture thancomputing devices. I mention the PDP-10 here to briefly recount another legend incomputer history (one that many of you have never heard). By taking this detour,I hope to give you a frame of reference from which to measure how incredibly longago this was in computer history.</P><P>It was at roughly that time that a Seattle, Washington, company began providingcomputer time sharing. The company reportedly took on two bright young men to testits software. These young men both excelled in computer science, and were rumoredto be skilled in the art of finding holes within systems. In exchange for testingcompany software, the young men were given free dial-up access to a PDP-10 (thiswould be the equivalent of getting free access to a private bulletin board system).Unfortunately for the boys, the company folded shortly thereafter, but the learningexperience changed their lives. At the time, they were just old enough to attendhigh school. Today, they are in their forties. Can you guess their identities? Thetwo boys were Bill Gates and Paul Allen.</P><P>In any event, by 1972, ARPANET had some 40 hosts (in today's terms, that is smallerthan many local area networks, or <I>LANs</I>). It was in that year that Ray Tomlinson,a member of Bolt, Beranek, and Newman, Inc., forever changed the mode of communicationon the network. Tomlinson created electronic mail.</P><P>Tomlinson's invention was probably the single most important computer innovationof the decade. E-mail allowed simple, efficient, and inexpensive communication betweenvarious nodes of the network. This naturally led to more active discussions and theopen exchange of ideas. Because many recipients could be added to an e-mail message,these ideas were more rapidly implemented. (Consider the distinction between e-mailand the telephone. How many people can you reach with a modern conference call? Comparethat to the number of people you can reach with a single e-mail message. For group-orientedresearch, e-mail cannot be rivaled.) From that point on, the Net was alive.</P><P>In 1974, Tomlinson contributed to another startling advance. He (in parallel withVinton Cerf and Robert Khan) invented the Transmission Control Protocol (TCP). Thisprotocol was a new means of moving data across the network bit by bit and then laterassembling these fragments at the other end.<BLOCKQUOTE> <P><HR><FONT COLOR="#000077"><B>NOTE:</B></FONT><B> </B>TCP is the primary protocol used on the Internet today. It was developed in the early 1970s and was ultimately integrated into Berkeley Software Distribution UNIX. It has since become an Internet standard. Today, almost all computers connected to the Internet run some form of TCP. In Chapter 6, "A Brief Primer on TCP/IP," I closely examine TCP as well as its sister protocols. <HR></BLOCKQUOTE><P>By 1975, ARPANET was a fully functional network. The groundwork had been doneand it was time for the U.S. government to claim its prize. In that year, controlof ARPANET was given to an organization then known as the United States Defense CommunicationsAgency (this organization would later become the Defense Information Systems Agency).</P><P>To date, the Internet is the largest and most comprehensive structure ever designedby humankind. Next, I will address some peripheral technological developments thathelped form the network and bring it to its present state of complexity. To do this,I will start with C.<H2><FONT COLOR="#000077"><B>What Is C?</B></FONT></H2><P><I>C</I> is a popular computer programming language, often used to write languagecompilers and operating systems. I examine C here because its development (and itsrelationship to the UNIX operating system) is directly relevant to the Internet'sdevelopment.</P><P>Nearly all applications designed to facilitate communication over the Internetare written in C. Indeed, both the UNIX operating system (which forms the underlyingstructure of the Internet) and TCP/IP (the suite of protocols used to traffic dataover the Net) were developed in C. It is no exaggeration to say that if C had neveremerged, the Internet as we know it would never have existed at all.</P><P>For most non-technical users, programming languages are strange, perplexing things.However, programming languages (and programmers) are the very tools by which a computerprogram (commonly called an <I>application</I>) is constructed. It may interest youto know that if you use a personal computer or workstation, better than half of allapplications you now use were written in the C language. (This is true of all widelyused platforms, including Macintosh.) In this section, I want to briefly discussC and pay some homage to those who helped develop it. These folks, along with PaulBaran, Ken Thompson, and a handful of others, are the grandparents of the Internet.</P><P>C was created in the early 1970s by Dennis M. Ritchie and Brian W. Kernighan.These two men are responsible for many technological advancements that formed themodern Internet, and their names appear several times throughout this book.</P><P>Let's discuss a few basic characteristics of the C programming language. To start,C is a compiled as opposed to an interpreted language. I want to take a moment toexplain this critical distinction because many of you may lack programming experience.<H3><FONT COLOR="#000077"><B>Interpreted Programming Languages</B></FONT></H3><P>Most programs are written in plain, human-readable text. This text is made upof various commands and blocks of programming code called <I>functions</I>. In interpretedlanguages, this text remains in human-readable form. In other words, such a programfile can be loaded into a text editor and read without event.</P><P>For instance, examine the program that follows. It is written for the PracticalExtraction and Report Language (Perl). The purpose of this Perl program is to getthe user's first name and print it back out to the screen.<BLOCKQUOTE> <P><HR><FONT COLOR="#000077"><B>NOTE:</B></FONT><B> </B>Perl is strictly defined as an interpreted language, but it does perform a form of compilation. However, that compilation occurs in memory and never actually changes the physical appearance of the programming code. <HR></BLOCKQUOTE><P>This program is written in plain English:</P><PRE><FONT COLOR="#0066FF">#!/usr/bin/perlprint "Please enter your first name:";$user_firstname = <STDIN>;chop($user_firstname);print "Hello, $user_firstname\n"print "Are you ready to hack?\n"</FONT></PRE><P>Its construction is designed to be interpreted by Perl. The program performs fivefunctions:</P><UL> <LI><FONT COLOR="#000000">Start the Perl interpreter<BR> <BR> </FONT> <LI><FONT COLOR="#000000">Print a message to the user, asking for his or her first name<BR> <BR> </FONT> <LI><FONT COLOR="#000000">Get the user's first name<BR> <BR> </FONT> <LI><FONT COLOR="#000000">Remove the carriage return at the end of the user input<BR> <BR> </FONT> <LI><FONT COLOR="#000000">Print a new message to the user, identifying him or her by name</FONT></UL><PRE></PRE><P>Interpreted languages are commonly used for programs that perform trivial tasksor tasks that need be done only once. These are sometimes referred to as <I>throwaway</I><I>programs</I>. They can be written quickly and take virtually no room on the localdisk.</P><P>Such interpreted programs are of limited use. For example, in order to run, theymust be executed on a machine that contains the command interpreter. If you takea Perl script and install it on a DOS-based machine (without first installing thePerl interpreter), it will not run. The user will be confronted with an error message(<TT>Bad command or file name</TT>). Thus, programs written in Perl are dependenton the interpreter for execution.</P><P>Microsoft users will be vaguely familiar with this concept in the context of applicationswritten in Visual Basic (VB). VB programs typically rely on runtime libraries suchas <TT>VBRUN400.DLL</TT>. Without such libraries present on the drive, VB programswill not run.⌨️ 快捷键说明
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