Network Security Considerations in the Internet in Java

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712 Network Security Considerations in the Internet
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Before delving into the technical aspects of network security in the following sections, let's conclude our introduction by relating our fictitious characters - Alice, Bob, and Trudy - to "real world" scenarios in today's Internet Let's begin with Trudy, the network intruder Can a "real world" network intruder really listen to and record network messages Is it easy to do so Can an intruder actively inject or remove messages from the network The answer to all of these questions is an emphatic "YES" A packet sniffer is a program running in a network attached device that
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What is Network Security
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passively receives all data-link-layer frames passing by the device's network interface In a broadcast environment such as an Ethernet LAN, this means that the packet sniffer receives all frames being transmitted from or to all hosts on the local area network Any host with an Ethernet card can easily serve as a packet sniffer, as the Ethernet interface card needs only be set to "promiscuous mode" to receive all passing Ethernet frames These frames can then be passed on to application programs that extract application-level data For example, in the telnet scenario shown in Figure 712, the login password prompt sent from A to B, as well as the password entered at B are "sniffed" at host C Packet sniffing is a double-edged sword - it can be invaluable to a network administrator for network monitoring and management (see 8) but also used by the unethical hacker Packet-sniffing software is freely available at various WWW sites, and as commercial products Professors teaching a networking course have been known to assign lab exercises that involve writing a packet-sniffing and application-level-data-reconstruction program
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Figure 71-2: packet sniffing Any Internet-connected device (eg, a host) necessarily sends IP datagrams into the network Recall from 4 that these datagrams carry the sender's IP address, as well as application-layer data A user with complete control over that device's software (in particular its operating system) can easily modify the device's protocols to place an arbitrary IP address into a datagram's source address field This is known as IP spoofing A user can thus craft an IP packet containing any payload (application-level) data it desires and make it appear as if that data was sent from an arbitrary IP host Packet sniffing and IP spoofing are just two of the more common forms of security "attacks" on the Internet These and other network attacks are discussed in the collection of essays [Denning 1997] A summary of reported attacks is maintained at the CERT Coordination Center [CERT 1999] Having established that there are indeed real bogeymen (aka "Trudy") loose in the Internet, what are the Internet equivalents of Alice and Bob, our two friends who need to communicate securely Certainly, "Bob" and "Alice" might be human user at two end systems, eg, a real Alice and a real Bob who really do want to exchange secure email (e g, a user wanting to enter a credit card in a WWW form for an electronic purchase) They might also be participants in an electronic commerce transaction, eg, a real Alice might want to securely transfer her credit card number to a WWW server to purchase an item on-line Similarly, a real Alice might want to interact with her back on-line As noted in [RFC 1636], however, the parties needing secure communication might also themselves be part of the network infrastructure Recall that the domain name system (DNS, see section 25), or routing daemons that exchange routing tables (see section 45) require secure communication between two parties The same is true for network management applications, a topic we examine in the following chapter An intruder that could actively interfere with, control, or
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