R

RADIUS (Remote Authentication Dial-In User Service)

A method widely used on the Internet by ISPs and large organizations to validate usernames and passwords for dial-up users, and to provide proper accounting. RADIUS is distributed in source-code form, making it highly modifiable.

random number

A number generated from a large set of numbers, using an algorithm that gives every number an equal probability of occurring. Random numbers are used as an ingredient in encryption keys; thus, a random number generator is a necessary element in creating unique keys that are unpredictable to an adversary.

RC4 (Rivest Cipher 4)

One of many symmetric key algorithms. Once a proprietary algorithm of RSA Data Security, Inc., RC4 creates keys of variable size which are called streaming ciphers; that is, they are used to encrypt a stream of data byte-by-byte as it goes by.

RC5 (Rivest Cipher 5)

A cipher that encrypts a block (many bytes) of data at a time. The RC5 algorithm enables the user to specify block size, key length, and how many times the encrypted message should be re-encrypted (referred to as encryption rounds).

related networks

A legacy term synonymous with secondary network.
See secondary network.

remote user

Someone you allow to access your office network, who is geographically removed from the office.

repeater

A network device that regenerates signals so that they can travel farther along a cable without losing or distorting data. A repeater is not as smart as a router, but it can relay messages between subnetworks that use different protocols or cable types.

reverse lookup; reverse DNS lookup

The opposite of a DNS lookup. DNS works like the phone book: in a DNS lookup, you have a name (such as domain.com) but you want the number (an IP address). In a reverse lookup, you have the number (e.g., 154.119.131.128), but you want to find the domain name associated with it (e.g., domain.com).

revocation

This term is most often used in the context of digital certificates. A Certificate Authority assures that all parties in a digital transaction are who they claim to be and that all documents are genuine. The Certificate Authority (CA) vouches for your digital certificate, which is like ID the CA issued you. If the CA subsequently finds out one of the parties misrepresented themselves (as happened in March of 2001, when Verisign issued digital certificates to imposters claiming to represent Microsoft), the CA can revoke the digital certificate. Thus, revocation is the retraction of certification or authorization.

RFC (Request for Comments)

RFC documents describe standards used or proposed for the Internet. Each RFC is identified by a number, such as RFC 1700. The Internet Engineering Task Force maintains RFCs on the World Wide Web, at www.ietf.org/rfc.html.

ring topology

A basic networking configuration in which all nodes are connected in a circle with no terminated ends on the cable.

route

1. The sequence of computerized devices through which information travels to reach its target machine. Each device the information travels through delineates one stage of the route, referred to as a "hop."

2. An entry stored on a computer, telling it how to reach other devices or networks. These entries can be automatically generated when you set up your network and can also be entered manually. They are stored in your local host's routing table.

router

A device, connected to at least two networks, that receives and sends data packets between those networks. Routers refer to packet headers and a forwarding table to decide where to forward packets to.

routine

See function.

RPC (Remote Procedure Call)

A protocol that allows a computer to ask some other computer to perform a task or service and return the result. The computer making the request is often referred to as a client, and the computer doing the task is called the server. The client computer does not need to know how to perform the task itself, it just sends an RPC request to a server and gets some result.

RUVPN (Remote User Virtual Private Networking)

RUVPN establishes a secure connection over the Internet between a remote computer and your protected network.