Online Glossary of Security Terms

This glossary contains a list of terms, abbreviations, and acronyms frequently used when discussing networks, security, firewalls, and technical products.

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T

TCP (Transmission Control Protocol)

A set of rules that enables a broad spectrum of different kinds of computers to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent, so it is considered "reliable." Most long-haul traffic on the Internet uses TCP.

TCP handshake

A three-step process computers go through when negotiating a connection with one another. Simplistically described, in a normal TCP handshake:

1. Computer A sends a SYN packet (for "synchronize");

2. Computer B acknowledges the connection attempt and sends back its own SYN packet (thus, a SYN/ACK packet), and

3. Computer A acknowledges Computer B's response.

Once both computers are synchronized and acknowledged, they can begin passing data back and forth. To learn how attackers might exploit this, see SYN flood attack.

TCP/IP (Transmission Control Protocol/Internet Protocol)

A common networking standard with the ability to connect a diverse array of systems. This is one of the underlying protocols of the Internet. For others, see ICMP, IP, TCP, and UDP.

TCP session hijacking

See session hijacking.

Telnet

A remote control program typically found on Unix systems in TCP/IP networks. A telnet client runs on your PC and connects it to a remote server on a network. You can then enter commands through the Telnet program and they will be executed as if you were entering them directly on the server console. This enables you to control the server and communicate with other servers on that remote network.

timestamping

Recording the time when an event happens (typically in a log) or when a piece of information is created or modified.

TLS (Transport Layer Security)

A general-purpose protocol for encrypting Web, e-mail, and other stream-oriented information sent over the Internet. TLS is a relatively recent (first published in 1999) derivative of the Secure Sockets Layer (SSL) version 3.0 protocol, and is described in RFCs 2246, 2712, 2817, and 2818.

token

Also called a security token or an authentication token. Something a person has that evidences validity, or identity. It is usually a hardware device that resembles a hand-held calculator, since it often has some sort of display and perhaps a keypad for entering numbers. Tokens achieve the goal of "two-factor authentication," considered a strong standard of security when validating who a user is, because accessing a network that uses tokens requires two factors: something the person knows (a password) and something the person has (the token).

tooltip

A name or phrase that appears when the mouse pointer pauses over a button or icon.

topology

A wiring configuration used for a network. Also referred to as a network's architecture.

transposition cipher

A cipher in which the plain text remains the same but the order of the characters is scrambled. Thus, the word "DOG" might become "OGD." Transposition is sometimes used as one step in the midst of several mathematical operations that, together, make up a cryptographic algorithm.

Triple-DES (3DES)

A cryptographic algorithm using three keys (rather than one or two). Triple DES is simply another mode of DES operation, where the DES algorithm is applied three times on the data to be encrypted, using a different key each time. 3DES is currently one of two US federal government standards for encrypting non-classified data.

Trojan Horse

Trojan horse secretly carries often-damaging software in a "plain wrapper." The plain wrapper is normally an e-mail file attachment from someone you may or may not know.

trust

Confidence in the honesty, integrity, or reliability of a person, company, or other entity. The concept also extends to believing that an unseen remote party is who he or she claims to be.

Trusted interface

The Ethernet port that connects it to your internal network. See Trusted network.

Trusted network

The private network which you intend your firewall to primarily protect. The Trusted network is usually where your most sensitive corporate resources reside or where home office employees do their work. This contrasts with the semi-public Optional network.

tunnel

In Virtual Private Networks (VPN), an encrypted connection between sites. Only the originator and the receiver of the message see it in its clear state. Any hacker trying to intercept the message en route gets nothing but a scrambled mess. Because the path of a VPN message has "light" (clear text) at each end but "darkness" (obscurity) at all the between-points, it is called, metaphorically, a VPN tunnel.

twisted-pair cable

A cable used for both network and telephone communications. Also known as UTP (unshielded twisted pair) and 10Base-T/100Base-T cable.