Glossary

Diffie-Hellman

DES has been cracked (data encoded using DES has been decoded by a third party).

Diffie-HellmanMethod to generate a symmetric key where two parties can publicly exchange values and generate the same symmetric key. Start with prime p and generator g, which may be publicly known (typically these numbers are from a well-known “Diffie-Hellman Group”). Each party selects a private value (a and b) and generates a public value (g**a mod p) and (g**b mod p). They exchange the public values. Each party then uses its private value and the other party's public value to generate the same symmetric key, (g**a)**b mod p and (g**b)**a mod p, which both evaluate to g**(a*b) mod p for future communication.

The Diffie-Hellman method must be combined with authentication to prevent man-in-the-middle or third party attacks (spoofing) attacks. Typically, it is combined with public/private key certificates (when sending the public value, each party signs the public value with its private key and includes a certificate).

Encryption The process of converting data from one format to another.

Encapsulating Security Payload (ESP)

The ESP provides confidentiality (encryption) and an anti-replay service. It should be used with authentication, either with the optional ESP authentication field (authenticated ESP) or nested in an Authentication Header message. Authenticated ESP also provides data origin authentication and connectionless integrity. When used in tunnel mode, ESP also provides limited traffic flow confidentiality.

ESP See Encapsulating Security Payload.

Filter A term used to refer to preferences in encryption, authentication, compression and protocol etc. for a particular end-user system.

HMAC Hashed Message Authentication Code. See also MAC.

IKE The Internet Key Exchange (IKE) protocol is used before the ESP or AH protocol exchanges to determine which encryption and/or authentication services will be used. IKE also manages the distribution and update of the symmetric (shared) encryption keys used by ESP and AH.

The IKE protocol is a hybrid of three other protocols: ISAKMP (Internet Security Association and Key Management Protocol), Oakley and SKEME. ISAKMP provides a framework for authentication and key exchange, but does not define the actual key exchange. (ISAKMP) defines most of the message format, with non-specific key-exchange information fields). The Oakley Key Determination protocol and SKEME protocol define key exchange techniques.

IPSec Policy IPSec Policies specify the rules according to which data is transferred securely. IPSec policies generally contain packet filter information and an action. The packet filter is used to select a policy for a packet and the action is applied to the packets using the policy

IPSec/QM SA See IPSec/Quick Mode Security Association.

306

Glossary