SuperVAULT: Superparamagnetic Volatile Auxiliary Tamper-Proof Storage

Memory security has recently come into the spotlight as attackers have stepped up their efforts to gain illicit access to sensitive data or cause denial-of-memory service via a variety of avenues, such as cold boot attacks, bus snooping, and physical probing or tampering. In this letter, we propose SuperVAULT, a novel secure storage solution for protecting secret data/keys by exploiting the superparamagnetic regime of nanomagnets. Through materials and dimensional engineering of the magnetic tunnel junction (MTJ) free layer, the energy barrier of spin-transfer torque magnetoresistive random-access memory (STT-MRAM) cells can be designed to lie in the range of the thermal energy ( {k_{\textrm {B}}T} ). Such superparamagnetic MTJ (s-MTJ) cells, with an {\mathcal {O}} (10 ns) retention time, need to be refreshed frequently. In the absence of data refresh (under attack conditions), the data they hold is thermally corrupted to a random state after an arbitrary but short amount of time. We leverage this property to devise a secure memory primitive and showcase its potential against cold boot and Boolean satisfiability (SAT) attacks. Further, the overheads for s-MTJ-based STT-MRAMs are shown to be promising for on-chip implementations.