IKE Key Negotiation

The IKE daemon, in.iked, negotiates and authenticates keying material for IPsec SAs in a secure manner. The daemon uses random seeds for keys from internal functions provided by the OS. IKE provides perfect forward secrecy (PFS). In PFS, the keys that protect data transmission are not used to derive additional keys. Also, seeds used to create data transmission keys are not reused. See the in.iked(1M) man page.

IKE Key Terminology

The following table lists terms that are used in key negotiation, provides their commonly used acronyms, and gives a definition and use for each term.

Table 17-1 Key Negotiation Terms, Acronyms, and Uses

Key Negotiation Term	Acronym	Definition and Use
Key exchange		The process of generating keys for asymmetric cryptographic algorithms. The two main methods are the RSA and the Diffie-Hellman protocols.
Diffie-Hellman algorithm	DH	A key exchange algorithm that provides key generation and key authentication. Often called authenticated key exchange.
RSA algorithm	RSA	A key exchange algorithm that provides key generation and key transport. The protocol is named for its three creators, Rivest, Shamir, and Adleman.
Perfect forward secrecy	PFS	Applies to authenticated key exchange only. In PFS, the key that is used to protect transmission of data is not used to derive additional keys. Also, the source of the key that is used to protect data transmission is never used to derive additional keys.
Oakley group		A method for establishing keys for Phase 2 in a secure manner. The Oakley method is used to negotiate PFS.

IKE Phase 1 Exchange

The Phase 1 exchange is known as Main Mode. In the Phase 1 exchange, IKE uses public key encryption methods to authenticate itself with peer IKE entities. The result is an Internet Security Association and Key Management Protocol (ISAKMP) security association (SA). An ISAKMP SA is a secure channel for IKE to negotiate keying material for the IP datagrams. Unlike IPsec SAs, the ISAKMP SAs are bidirectional, so only one security association is needed.

How IKE negotiates keying material in the Phase 1 exchange is configurable. IKE reads the configuration information from the /etc/inet/ike/config file. Configuration information includes the following:

Global parameters, such as the names of public key certificates
Whether perfect forward secrecy (PFS) is used
The interfaces that are affected
The security protocols and their algorithms
The authentication method

The two authentication methods are preshared keys and public key certificates. The public key certificates can be self-signed. Or, the certificates can be issued by a certificate authority (CA) from a public key infrastructure (PKI) organization.

IKE Phase 2 Exchange

The Phase 2 exchange is known as Quick Mode. In the Phase 2 exchange, IKE creates and manages the IPsec SAs between systems that are running the IKE daemon. IKE uses the secure channel that was created in the Phase 1 exchange to protect the transmission of keying material. The IKE daemon creates the keys from a random number generator by using the /dev/random device. The daemon refreshes the keys at a configurable rate. The keying material is available to algorithms that are specified in the configuration file for IPsec policy, ipsecinit.conf.

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