IPsec Security Associations

An IPsec security association (SA) specifies security properties that are recognized by communicating hosts. A single SA protects data in one direction. The protection is either to a single host or to a group (multicast) address. Because most communication is either peer-to-peer or client-server, two SAs must be present to secure traffic in both directions.

The following three elements uniquely identify an IPsec SA:

• The security protocol (AH or ESP)

• The destination IP address

• The security parameter index (SPI)

The SPI, an arbitrary 32-bit value, is transmitted with an AH or ESP packet. The ipsecah(7P) and ipsecesp(7P) man pages explain the extent of protection that is provided by AH and ESP. An integrity checksum value is used to authenticate a packet. If the authentication fails, the packet is dropped.

Security associations are stored in a security associations database (SADB). A socket-based administration engine, the pf_key interface, enables privileged applications to manage the database.

• For a more complete description of the IPsec SADB, see Security Associations Database for IPsec.

• For more information about how to manage the SADB, see the pf_key(7P) man page.

Key Management in IPsec

Security associations (SAs) require material to create the keys for authentication and for encryption. The managing of this keying material is called key management. The Internet Key Exchange (IKE) protocol handles key management automatically. You can also manage keys manually with the ipseckey command.

SAs on IPv4 and IPv6 packets can use either method of key management. Unless you have an overriding reason to use manual key management, automatic key management is preferred. For example, to interoperate with systems other than Solaris systems might require manual key management.

• The in.iked daemon provides automatic key management. For a description of IKE, see Chapter 22, Internet Key Exchange (Overview). For more information on the in.iked daemon, see the in.iked(1M) man page.

• The ipseckey command provides manual key management. For a description of the command, see Utilities for Key Generation in IPsec. For a detailed description of the ipseckey command options, see the ipseckey(1M) man page.