Security association 

SA 

A unique connection between two nodes on a network. The connection is defined by a triplet: a security protocol, a security parameter index, and an IP destination. The IP destination can be an IP address or a socket. 

Security associations database 

SADB 

Database that contains all active security associations. 

Security parameter index 

SPI 

The indexing value for a security association. An SPI is a 32-bit value that distinguishes among SAs that have the same IP destination and security protocol. 

Security policy database

SPD 

Database that determines if outbound packets and inbound packets have the specified level of protection. 

Key exchange 

The process of generating keys for asymmetric cryptographic algorithms. The two main methods are RSA protocols and the Diffie-Hellman protocol. 

Diffie-Hellman protocol 

DH 

A key exchange protocol that involves key generation and key authentication. Often called authenticated key exchange.

RSA protocol 

RSA 

A key exchange protocol that involves key generation and key distribution. The protocol is named for its three creators, Rivest, Shamir, and Adleman. 

Internet Security Association and Key Management Protocol 

ISAKMP 

The common framework for establishing the format of SA attributes, and for negotiating, modifying, and deleting SAs. ISAKMP is the IETF standard for handling IPsec SAs.