Cloud computing relies on hypervisors to isolate virtual machines running on shared hardware. Since perfect isolation is difficult to achieve, sharing hardware induces threats. Covert channels were demonstrated to violate isolation and, typically, allow data exfiltration. Several covert channels have been proposed that rely on the processor’s cache. However, these covert channels are either slo...

While the secure transaction schedulers in multilevel secure database systems synchronize transactions cleared at different security levels, they must consider the problem of covert channel. Through the covert channel, malicious users leak secret information in a way of intentional interference among the transactions that they invoked. Much work had been done for closing the covert channel. Alt...

Covert timing channels aim at transmitting hidden messages by controlling the time between transmissions of consecutive payload packets in overt network communication. Previous results used encoding mechanisms that are either easy to detect with statistical analysis, thus spoiling the purpose of a covert channel, and/or are highly sensitive to channel noise, rendering them useless in practice. ...

We present a protocol for sending data over a common class of low-bandwidth covert channels. Covert channels exist in most communications systems and allow individuals to communicate truly undetectably. However, covert channels are seldom used due to their complexity. Our protocol is both practical and secure against attack by powerful adversaries. We implement our protocol on a standard platfo...

A general framework for exploiting covert channels in combinatorial games is presented. The framework is applicable to all combinatorial games, including Chess and Go, but is applied to the game of Tic-Tac-Toe for ease of experimental analysis. The security and capacity of the resulting covert channel are analyzed experimentally. By considering the ways in which a passive adversary can attempt ...

Covert channels may be dangerous to company networks as they can lead to the leakage of confidential information. However, it is hard to assess what bandwidth of a covert channel poses a serious threat. Generally, it depends on the security policy that is implemented by the organisation concerned. The ideal case will be to eliminate all possibilities of hidden communication, but practically it ...

Lost audio packet steganography (LACK) is a steganography technique established on the VoIP network. LACK provides a high-capacity covert channel over VoIP network by artificially delaying and dropping a number of packets in use to convey stegnogram. However, the increasing loss of packets will hurt the quality of the VoIP service. The quality deterioration will not only affect the legitimate V...

Previous research has demonstrated categorical perception (CP) of facial expressions from American Sign Language (ASL) in hearing, English-speaking non-signers. Notably, CP was observed even for faces with no obvious linguistic labels in English, suggesting the existence of covert categories based on nonlinguistic facial properties. However, in the earlier work, CP was assessed using memory pro...

In this paper, we evaluate available steganographic techniques for SIP (Session Initiation Protocol) that can be used for creating covert channels during signaling phase of VoIP (Voice over IP) call. Apart from characterizing existing steganographic methods we provide new insights by introducing new techniques. We also estimate amount of data that can be transferred in signalling messages for t...