The fabrication process of integrated circuits (ICs) is complex and requires the use of off-shore foundries to lower the costs and to have access to leading-edge manufacturing facilities. Such an outsourcing trend leaves the possibility of inserting malicious circuitry (a.k.a. hardware Trojans) during the fabrication process, causing serious security concerns. Hardware Trojans are very hard and expensive to detect and can disrupt the entire circuit or covertly leak sensitive information via a subliminal channel. In this paper, we propose a formal model for assessing the security of ICs whose fabrication has been outsourced to an untrusted off-shore manufacturer. Our model captures that the IC specification and design are trusted but the fabrication facility(ies) may be malicious. Our objective is to investigate security in an ideal sense and follows a simulation based approach that ensures that Trojans cannot release any sensitive information to the outside. It follows that the Trojans’ impact in the overall IC operation, in case they exist, will be negligible up to simulation. We then establish that such level of security is in fact achievable for the case of a single and of multiple outsourcing facilities. We present two compilers for ICs for the single outsourcing facility case relying on verifiable computation (VC) schemes, and another two compilers for the multiple outsourcing facilities case, one relying on multi-server VC schemes, and the other relying on secure multiparty computation (MPC) protocols with certain suitable properties that are attainable by existing schemes.