Network authentication service protocols

Kerberos protocol

The Kerberos protocol provides third-party authentication where users prove their identities to a centralized server, called a Kerberos server or key distribution center (KDC), which issues tickets to the users. The users can then use these tickets to prove their identities on the network. The ticket eliminates the need for multiple sign-ons to different systems. The Network Authentication Service APIs that the IBM i environment supports originated from Massachusetts Institute of Technology and have become the de facto standard for using the Kerberos protocol.

Security environment assumptions

The Kerberos protocol assumes that all data exchanges occur in an environment where packets can be inserted, changed, or intercepted at will. Use Kerberos as one layer of an overall security plan. Although the Kerberos protocol allows you to authenticate users and applications across your network, you should be aware of some limitations when you define your network security objectives:

• The Kerberos protocol does not protect against denial-of-service attacks. There are places in these protocols where an intruder can prevent an application from participating in the correct authentication steps. Detection and solution of such attacks are typically best left to human administrators and users.
• Key sharing or key theft can allow impersonation attacks. If intruders somehow steal a principal's key, they will be able to masquerade as that user or service. To limit this threat, prohibit users from sharing their keys and document this policy in your security regulations.
• The Kerberos protocol does not protect against typical password vulnerabilities, such as password guessing. If a user chooses a poor password, an attacker might successfully mount an offline dictionary attack by repeatedly attempting to decrypt messages that are encrypted under a key derived from the user's password.

Kerberos sources

Generic Security Services (GSS) APIs

Generic Security Services Application Programming Interfaces (GSS APIs) provide security services generically and are supported by a range of security technologies, like the Kerberos protocol. This allows GSS applications to be ported to different environments. Because of this reason, it is recommended that you use these APIs instead of Kerberos APIs. You can write applications that use GSS APIs to communicate with other applications and clients in the same network. Each of the communicating applications plays a role in this exchange. Using GSS APIs, applications can perform the following operations:

• Determine another application's user identification.
• Delegate access rights to another application.
• Apply security services, such as confidentiality and integrity, on a per-message basis.

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