Abstract
Covert channels aim to hide the existence of communication between two or more parties. Such channels typically utilise pre-existing overt data transmissions to carry hidden messages. Recently, Murdoch proposed a temperature-based covert channel where information is transmitted by remotely inducing and measuring changes of temperature of an intermediate/target host. The channel was invented mainly for the purpose of attacking anonymous servers, but could also be used for general-purpose covert communications. We propose a method for estimating the channel capacity, which largely depends on the intermediate host. Evaluation of two different intermediate hosts shows upper bounds for the channel capacity of 10.8– 15.4 and 16.4–21.1 bits per hour depending on the noise.