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Certificates are typically requested from a certificate server at the site of a CA. To request a certificate, you send a certificate signing request (CSR) to the CA's certificate server, along with some other information to identify yourself. The information required is determined by the CA, and it varies from CA to CA. The CA staff then processes your CSR and generates a public and private key pair for you if they grant your request. They will most likely send you a public key over e-mail, but they should require that you retrieve your private key from them using some secure means, such as a secure Web connection download. Remote Authentication with CHAP Challenge Handshake Authentication Protocol (CHAP) is a protocol that can be used when a remote client needs to authenticate itself to a network server or when two routers need to authenticate themselves to each other to begin a Point-to-Point Protocol (PPP) session. CHAP avoids transmission of the actual password on the established connection. The authentication process used by CHAP involves a three-way handshake in which the network access server (NAS) sends a challenge to the client consisting of the session ID and a random string of data to the remote client.

The remote client uses a Message Digest 5 (MD5) function hash to return the following information: The user name

A password As discussed in 3, MD5 takes the variable-length string of data (the information just listed), and produces a 128-bit message digest that is used for validation. CHAP protects against replay attacks by using an arbitrary challenge string for each authentication attempt and protects against remote client impersonation by sending repeated challenges at unpredictable intervals to the remote client throughout the duration of the connection. Tokens A token is a device that can be issued to a user for use in the authentication process. For example, there are token devices that, when enabled, synchronize with a server. Each minute the numbers in the server and on the device change to a predetermined number, as long as the battery in the device is working. For a user to authenticate, he or she must type in the number on the display, which must match the number in the server for the user to be authenticated. Tokens are often small handheld devices, with or without keypads, that can range in size from a credit

card to a small pocket calculator. Among other forms, they can be smart cards with small computer chips in them, requiring a reader when used with a PC. One type of authentication process used with hardware tokens involves a challenge-response process: 1. 1. Enter your user name at a workstation and send it to the authentication server. 1. 2. 2. The server responds with a challenge to the token. 2. 3. 3. You reply using the token (or information provided by the token). 3. 4. 4. The server validates the information you provided and authenticates you. 4. Tokens are difficult to duplicate and are generally tamper resistant. Some can be carried with you for use on any workstation, although others require appropriate hardware peripherals and software on a workstation. Although tokens offer reliable security, they can be costly and difficult to deploy in an enterprise environment. Tokens can either provide a one-time-use password or store information about the user. The user information can be a certificate and a password, as with smart cards. Smart card technologies provide strong security through encryption as well as access control. Smart cards require a reader that is used when the authentication is required. Biometrics Biometric authentication is an automated method of identifying a person based on a physical characteristic, such as a thumbprint or the retina of his or her eye. Using this type of authentication requires comparing a registered sample against a new captured biometric sample, for example, a fingerprint captured during a logon. The biometric authentication mechanism typically has two modes, enrolling and verifying. Enrolling For initial use of the biometric, a system administrator must enroll each user to verify that each individual being enrolled is authorized. The enrolling process includes storing the user's biological feature that will be used later to verify the user's identity. This is typically acquired by using a sensor (hardware device) that can record the particular feature, such as a thumbprint scanner. Verifying For the verification process, the user has a sensor on his or her computer that can capture the same biological information that was used for enrollment and then transmit that information to the authenticating server. The server can then compare the information presented by the user with the stored information to validate the user.