Data Protection and Security

V

Access Control

V.VI

Covert Channels

A covert channel is an information flow that is not controlled by a security mechanism. In BLP, you could use the access control mechanism itself to construct a covert channel.

• A low level subject makes an object "dummy.obj" at its own level.
• Its high level accomplice either upgrades the security level of dummy.obj to high or leaves it unchanged.
• Later, the low level subject tries to read dummy.obj. Success or failure of this request disclose the action of the high-level subject. One bit of information has flown from high to low.
  

Other Examples for Covert Channels:

• Timing Channels
• Resource State
• Hidden Information in downgraded documents

Commonly used techniques for reducing covert channels:

• Reduce abusable functionality
• High level processes get lowest resource allocation priority and can be preempted by low level processes.
• Random delays, clock noise, randomized resource availability.
• Auditing the use of known channels
• Polyinstantiation
  

Animation V.VI-I: Covert channel animation. [click to enlarge]

V.VI.I Q