Biblio

We would like to compute RSA signatures with the help of a Hardware Security Module (HSM). But what can we do when we want to use a certain public exponent that the HSM does not allow or support? Surprisingly, this scenario comes up in real-world settings such as code-signing of Intel SGX enclaves. Intel SGX enclaves have to be signed in order to execute in release mode, using 3072-bit RSA signature scheme with a particular public exponent. However, we encountered commercial hardware security modules that do not support storing RSA keys corresponding to this exponent. We ask whether it is possible to overcome such a limitation of an HSM and answer it in the affirmative (under stated assumptions). We show how to convert RSA signatures corresponding to one public exponent, to valid RSA signatures corresponding to another exponent. We define security and show that it is not compromised by the additional public knowledge available to an adversary in this setting.

Sensitive computation often has to be performed in a trusted execution environment (TEE), which, in turn, requires tamper-proof hardware. If the computational fabric can be tampered with, we may no longer be able to trust the correctness of the computation. We study the (wild and crazy) idea of using computational platforms in space as a means to protect data from adversarial physical access. In this paper, we propose SpaceTEE - a practical implementation of this approach using low-cost nano-satellites called CubeSats. We study the constraints of such a platform, the cost of deployment, and discuss possible applications under those constraints. As a case study, we design a hardware security module solution (called SpaceHSM) and describe how it can be used to implement a root-of-trust for a certificate authority (CA).