Editing Covert channel (section)

===TCSEC criteria===

The [[TCSEC|Trusted Computer Security Evaluation Criteria]] (TCSEC) was a set of criteria, now deprecated, that had been established by the [[National Computer Security Center]], an agency managed by the United States' [[National Security Agency]].

Lampson's definition of a ''covert channel'' was paraphrased in the TCSEC<ref>[http://www.fas.org/irp/nsa/rainbow/tg030.htm NCSC-TG-030, ''Covert Channel Analysis of Trusted Systems (Light Pink Book)'', 1993] from the [[United States Department of Defense]] (DoD) [[Rainbow Series]] publications.</ref> specifically to refer to ways of transferring information from a higher classification compartment to a lower classification.  In a shared processing environment, it is difficult to completely insulate one process from the effects another process can have on the operating environment.  A covert channel is created by a sender process that modulates some condition (such as free space, availability of some service, wait time to execute) that can be detected by a receiving process.

The TCSEC defines two kinds of covert channels:
*[[Storage channels]] - Communicate by modifying a "storage location", such as a hard drive.
*[[Timing channels]] - Perform operations that affect the "real response time observed" by the receiver. 
The TCSEC, also known as the ''Orange Book'',<ref>[http://csrc.ncsl.nist.gov/publications/secpubs/rainbow/std001.txt 5200.28-STD], [[TCSEC|''Trusted Computer System Evaluation Criteria (Orange Book)'', 1985]]  {{Webarchive|url=https://web.archive.org/web/20061002160143/http://csrc.ncsl.nist.gov/publications/secpubs/rainbow/std001.txt |date=2006-10-02 }} from the DoD [[Rainbow Series]] publications.</ref> requires analysis of covert storage channels to be classified as a B2 system and analysis of covert timing channels is a requirement for class B3.