Tools to help you resolve and network problems

C

cable segment: A section of network cable separated by switches, routers, or bridges.
cascade: A command that arranges windows so that they are overlapped, with the active window in front.
Category 3 cabling: A cabling specification for 10BaseT networks, which are capable of handling up to 10 mega bits of data per second.
Category 5 cabling: A cabling specification for 100BaseT networks, which are capable of handling up to 100 mega bits of data per second.
CBC (Cipher Block Chaining): A technique commonly used by encryption algorithms like Data Encryption Standard (DES) - CBC, where a plain text message is broken into sequential blocks. The first block is encrypted using a given cipher, creating cipher text. That cipher text is used to encrypt the second block of plain text. This pattern continues, with each subsequent block of plain text being encrypted using the cipher text encrypted just before it.
CD-ROM (Compact Disc Read-Only Memory): A compact disk on which data is stored.
certificate: An electronic document attached to someone's public key by a trusted third party, which attests that the public key belongs to a legitimate owner and has not been compromised. Certificates are intended to help you verify that a file or message actually comes from the entity it claims to come from.
certificate authority (CA): A trusted third party (TTP) who verifies the identity of a person or entity, then issues digital certificates vouching that various attributes (e. g., name, a given public key) have a valid association with that entity.
certificate revocation list: See CRL.
channel: 1. A communications path between two computers or devices.
CHAP (Challenge Handshake Authentication Protocol): A type of authentication where the person logging in uses secret information and some special mathematical operations to come up with a number value. The server he or she is logging into knows the same secret value and performs the same mathematical operations. If the results match, the person is authorized to access the server. One of the numbers in the mathematical operation is changed after every log-in, to protect against an intruder secretly copying a valid authentication session and replaying it later to log in. Often contrasted with PAP.
CIDR (Classless Inter-Domain Routing): Originally, Internet addresses were classified as A, B, or C. The early classification system did not envision the massive popularity of the Internet, and is in danger of running out of new unique addresses. CIDR is an addressing scheme that allows one IP address to designate many IP addresses. A CIDR IP address looks like a normal IP address except that it ends with a slash followed by a number; for example, 192.168.0.0/16. CIDR is described in RFC 1519.
cipher block chaining: See CBC.
cipher text: The result of encrypting either characters or bits using some algorithm. Cipher text is unreadable until it is decrypted.
Class A, Class B, Class C: See Internet address class.
clear-signed message: A message that is digitally signed but not encrypted.
See digital signature.
clear text: Characters in a human readable form prior to encryption or after decryption. Also called plain text.
client: A computer process that requests a service from another computer and accepts the server's responses.
Client/Server: A network computing system in which individual computers (clients) use a central computer (server) for services such as file storage, printing, and communications.
See peer-to-peer.
coax (coaxial) cable: A type of cable, used in Ethernet networking, with a solid central conductor surrounded by an insulator, in turn surrounded by a cylindrical shield woven from fine wires. The shield minimizes electrical and radio frequency interference.
cold boot: The process of starting a computer by turning on the power to the system unit.
collisions: Conflicts that occur when two packets are sent over the network simultaneously. When packets collide, both packets are rejected. Ethernet automatically resends them at altered timing.
compress: To compact a file or group of files so that they occupy less disk space.
See also decompress.
compression function: A function that accepts input and returns a shorter output. One common program that performs this is WinZIP.
Control Panel: The set of Microsoft Windows programs used to change system hardware, software, and settings.
conventional encryption: See symmetric algorithm.
cookie: A text file passed from the Web server to the Web client (a user's browser) that is used to identify a user and could record personal information such as ID and password, mailing address, credit card number, and more. A cookie is what enables your favorite Web site to "recognize" you each time you revisit it.
coprocessor: A microprocessor designed to assist another microprocessor in specific functions, such as handling complex mathematics or graphics, and to temporarily reduce the workload of the other microprocessor.
CPU (Central Processing Unit): The microprocessor chip that interprets and carries out most of the instructions you give your computer. Also, simply, a term for a computer.
cracker: Another term for someone who attempts to defeat network security measures, with hostile intent. Commonly used in popular media as a synonym for hacker.
CRL (Certificate Revocation List): An up-to-date list of previously issued certificates that are no longer valid.
See also revocation.
cross-certification: A status where two or more organizations or certificate authorities share some level of trust.
crossover cable: Ethernet cables have multiple wires inside them. Some are dedicated to sending; some are dedicated to receiving. A crossover cable is a special cable in which the receive and send wires cross so that the sending leads on one device can directly connect to the receiving leads on the other device.
cross-site scripting: An attack performed through Web browsers, taking advantage of poorly-written Web applications. Cross-site scripting attacks can take many forms. One common form is for an attacker to trick a user into clicking on a specially-crafted, malicious hyperlink. The link appears to lead to an innocent site, but the site is actually the attacker's, and includes embedded scripts. What the script does is up to the attacker; commonly, it collects data the victim might enter, such as a credit card number or password. The malicious link itself might also collect the victim's cookie data.
cryptanalysis: The art or science of transferring cipher text into plain text without initial knowledge of the key used to encrypt the plain text.
CRYPTOCard: One element in a proprietary authentication system, which uses an offline card containing a large secret key to answer security "challenges" from the network. The large number inside the card, called a key, is like a hard-to-guess password used in encrypting and decrypting. The key is never stored on a computer, which increases its safety against unauthorized discovery.
cryptography: The art and science of encoding and decoding messages using mathematical algorithms that utilize a secret key. The concept has broadened to include managing messages that have some combination of: privacy (by being unreadable to anyone but the sender and receiver); integrity (not modified while en route), and non-repudiation (digitally signed in such a way that the originator cannot plausibly claim he or she did not originate it).
CSLIP (Compressed Serial Line Internet Protocol): A protocol for exchanging IP packets over a serial line, which compresses the headers of many TCP/IP packets.