Packet - The unit of data sent across a packet switching network. the term is used loosely. While some TCP/IP literature uses it to refer specifically to data sent across a physical network, other literature views an entire TCP/IP internet as a packet switching network and describes IP datagrams as packets.

Packet Filter - Inspects each packet for user defined content, such as an IP address but does not track the state of sessions. This is the least secure type of firewall.

Packet Filtering - A feature incorporated into routers and bridges to limit the flow of information based on pre-determined communications such as source, destination, or type of service being provided by the network. Packet filters let the administrator limit protocol specific traffic to one network segment, isolate email domains, and perform many other traffic control functions.

Packet Sniffer - A device or program that monitors the data traveling between computers on a network. Packet Switched Network - A network of devices that communicate between each other by transmitting packets addressed to particular destinations. A transmission technique that maximizes the use of digital transmission facilities by transmitting packets of digital data from many customers simultaneously on a single communications channel.

Packet Switching - The process of routing and transferring data by means of addressed packets so that a channel is occupied during the transmission of the packet only, and upon completion of the transmission the channel is mad available for the transfer of other traffic.

Packet Switching Network (PSN) - A value-added network offering long distance computer communications allowing the user to access a remote computer, by dialing a local node, or access point. PSNs use high-speed digital links, which can be land lines or satellite communications. They use synchronous communications, usually with the X.25 protocol. The original ARPANET was a packet-switching network, as was Telenet and TYMNET.

Parallel - Means of communication in which digital data is sent multiple bits at a time, with one line per bit.

Partition - A discrete portion of a disk, configured using the format program in Unix, and Fdisk in DOS.

Passive Attack - Attack which does not result in an unauthorized state change, such as an attack that only monitors and/or records data.

Passive Threat - The threat of unauthorized disclosure of information without changing the state of the system. A type of threat that involves the interception, not the alteration, of information.

Passphrase - A sequence of characters, longer than the acceptable length of a password, that is transformed by a password system into a virtual password of acceptable length.

passwd - A Unix command to change a user's password.

Password - A protected word or string of characters that identifies or authenticates a user for access to a specific resource such as a system, data set, file, record, and so forth.

Password Shadowing - Password shadowing is a security system where the encrypted password field of /etc/passwd file is replaced with a special token and the encrypted password is stored in a separate file which is not readable by normal system users.

Race Conditions - Races between processes operating on a system. Such conditions can be abused by skillful attackers.

RAID (Redundant Array of Inexpensive Disks) - A disk subsystem composed of more than one disk drive to provide improved reliability, response time, and/or storage capacity.

RAM (Random Access Memory) - Also known as read-write memory; the memory used to execute application programs.

Rainbow - Any of several series of technical manuals distinguished by cover color. The original rainbow series was the NCSC security manuals. See Orange Book.

RARP (Reverse Address Resolution Protocol) - The TCP/IP protocol a diskless machine uses at startup to find its IP address. The machine broadcasts a request that contains its physical hardware address and a server responds by sending the machine its IP address. RARP takes its name and message format from another IP address resolution protocol, ARP rcp - A Unix command to copy files to and from remote systems. See sunrpc

RFC (Request For Comment) - One of a long-established series of Internet informational documents and standards.

RFS (Remote File Service) - One of the many distributed file system network protocols that allow one computer to use the files and peripherals of another as if they were local. Developed by AT&T and adopted by other vendors as a part of Unix V. see SMB

Read-only - A file, program, directory, disk, file system etc. that is readable by authorized users but cannot be edited due to not having write privileges.

Repeater - A device that amplifies and regenerates signals so they can travel on additional cable segments. Replicator - Any program that acts to produce copies of itself; a program, a worm, a fork bomb or virus. It is even claimed by some that UNIX and C are the symbiotic halves of an extremely successful replicator.

Repudiation - The denial by someone who did something in a system (e.g. sent a message) that he actually did perform that action.

Reserved Words - A word with a specific, built-in meaning to a compiler; all commands in programming languages and operating systems are known as such.

Resident Memory - Section of the central processing unit that, during processing, holds program instructions, input data, calculation results, and data to be output.

Residual Risk - The portion of risk that remains after security measures have been applied. Response Time - The time a system or functional unit takes to react to a given input.

Retro-Virus - A retro-virus is a virus that waits until all possible backup media are infected too, sot that it is not possible to restore the system to an uninfected state.

Reverse Engineering - A process by which people take a computer chip or machine-code executable version of a program and figure out what the program or chip is doing.

rexd - This Unix command is the Sun RPC server for remote program execution. This daemon is tarted by inetd whenever a remote execution request is made. see rpc

RF (Radio Frequency) - A broad spectrum of electromagnetic radiation. RF radiation is used primarily for the purpose of communications.

RFC (Request For Comments) - The name of a series of notes that contain surveys, measurements, ideas, techniques, and observations, as well as proposed and accepted TCP/IP protocol standards. RFCs are edited but not refereed. They are available on-line from the Network Information Center.

Risk - The possibility that a particular system vulnerability will be exploited.

Risk Assessment - A study of the vulnerabilities, threats, likelihood, loss or impact, and theoretical effectiveness of security measures. The process of evaluating threats and vulnerabilities, known and postulated, to determine expected loss and establish the degree of acceptability to system operations.

Risk Management - The total process to identify, control, and minimize the impact of uncertain events. The objective of the risk management program is to reduce risk and obtain and maintain DAA approval.

RJE (Remote Job Entry) - Refers to the programs used to submit processing jobs from terminals. rlogin - Unix command to remotely login to another machine. User must have a user account on the remote machine.

rm - A Unix command to remove files from a directory. The "rm *" will remove all files from a subdirectory, and the most dangerous is "rm * -r" which will recursively remove files and entire subdirectories without warning.

Robust - Said of a system that has demonstrated an ability to recover gracefully from the whole range of exceptional inputs and situations in a given environment. One step below bulletproof.

ROM (Read-Only Memory) - Memory containing preloaded programs that cannot be rewritten or changed by the CPU.

Root - By extension, the privileged system-maintenance login on any OS. The superuser account with user name `root' that ignores permission bits, user num ber 0 on a Unix system. The top node of a system directory structure.

Rootkit - A hacker security tool that captures passwords and message traffic to and from a computer. A collection of tools that allows an attack hacker to provide a backdoor into a system, collect information on other systems on the network, mask the fact that the system is compromised, and much more. Rootkit is a classic example of Trojan Horse software. Rootkit is widely distributed for a wide range of operating systems.

Router - An interconnection device that is similar to a bridge but serves packets or frames containing certain protocols. Routers link LANs at the network layer.

Routing Control - The application of rules during the process of routing so as to chose or avoid specific networks, links or relays.

rpc - This is a set of library routines for performing remote procedure calls from one machine to other machines across a network.

rsh - A Unix command that starts a remote shell on a remote machine, executing a command on the remote machine. On some systems, rsh refers to the restricted shell.

RS232 - A standard by EIA that specifies the electrical characteristics of slow speed interconnections between terminals and computers or between two computers. The specification limits speed to 20 Kbps and distance to 500 feet, but many manufacturers support speeds of 38.4 Kbps and/or longer distances.

RTT (Round Trip Time) - A measure of delay between two hosts. The round trip time consists of teh total time taken for a single packet or datagram to leave one machine, reach the other, and return.