Abstract: Covert network timing channels control time between transmissions of packets in overt network communication and transmits hidden messages. This paper presents an overview of different concepts of covert timing channels such as types, features and properties. There is range of terms used for security of information such as encryption, covert channels, network steganography or information hiding in network protocols. Information is hided into network protocols in case of covert channel, but information is hided into content in case of steganography. Different applications such as VoIP, SSH use covert timing channels for the purpose of security. In earlier days, encryption was only the parameter used for security; so information was not secure however simply using encryption does not prevent detection of communication patterns, so various techniques are developed. The main properties of covert timing channels are undetectability and robustness. Unauthorized access from criminals, hackers & terrorists is avoided by using covert timing channels etc. But there are some negativities of covert timing channels, e.g. terrorists misuse covert channels to coordinate their actions. This paper also discusses about use of covert timing channels and types along with applications and problems occur in covert timing channels.

Keywords: Covert Timing Channels, Security, Typesof covert channels.