Building higher resolution synthetic clocks for signaling in covert timing channels

We report on our study of a timing channel countermeasure within the context of the National Computer Security Center´s evaluation of the Boeing multilevel secure local area network (MLS LAN) secure network server (SNS). The countermeasure restricts the throughput of internal timing channels by explicitly limiting the time reference clock granularity that is made available to untrusted processes running on the SNS. We describe details of an internal covert timing channel implementation experiment, which was used to informally validate certain assumptions and results in the formal mathematical covert channel analysis. More specifically, we describe a method used for synthetically generating a fine-grained signaling clock to achieve timing channel throughput that approaches the capacity derived in Boeing´s worst-case analysis of timing channel capacities