Run-Time Effect by Inserting Hardware Trojans, in Combinational Circuits

Abstract

Integrated circuits can be modified with malicious circuitries, like hardware trojans. The use of these circuitries, is either to leak confidential information, or disable security fence of a system, or even to the total destroy of the chip. In this work, several shift registers and a set of logic gates were used to implement key generators. A malicious hardware trojan circuit was added in the combinational circuit, to leak information that were generated. Only a few logical gates are needed to effectively trigger the malicious circuitry, in combination with a flip-flop. These additional gates, have to be included between the shift registers, to be triggered by certain signals, and not to leak in every clock cycle. Taking the advantage of the trigger effect, the malicious circuitry is not delaying the key generators. By implementing the above system, the ability of a hardware trojan to be stealthy under many circumstances, is proven. It is also introduced, from the low demand of logic gates, the little space that is obtained as the effect. It is also proven by the implementation, the very low cost of additional time, which is really needed to perform the leak. Merging those two advantages, the modified circuit that is resulted, is hard to be detected, by a number of applied methods. In particular, in this work a hardware trojan is implemented and added in a stream cipher hardware integration. It is proven, by the implementation results, that the spatial burden is about 2% while the temporal burden is about 3%.