We present a Horn-clause-based framework for analysing security protocols that use platform configuration registers (PCRs), which are registers for maintaining state inside the Trusted Platform Module (TPM). In our model, the PCR state space is unbounded, and our experience shows that a naïve analysis using ProVerif or SPASS does not terminate. To address this, we extract a set of instances of the Horn clauses of our model, for which ProVerif does terminate on our examples. We prove the soundness of this extraction process: no attacks are lost, that is, any query derivable in the more general set of clauses is also derivable from the extracted instances. The effectiveness of our framework is demonstrated in two case studies: a simplified version of Microsoft Bitlocker, and a digital envelope protocol that allows a user to choose whether to perform a decryption, or to verifiably renounce the ability to perform the decryption.
PKCS#11 defines an API for cryptographic devices that has been widely adopted in industry. However, it has been shown to be vulnerable to a variety of attacks that could, for example, compromise the sensitive keys stored on the device. In this paper, we set out a formal model of the operation of the API, which differs from previous security API models notably in that it accounts for non-monotonic mutable global state. We give decidability results for our formalism, and describe an implementation of the resulting decision procedure using the model checker NuSMV. We report some new attacks and prove the safety of some configurations of the API in our model. We also analyse proprietary extensions proposed by nCipher (Thales) and Eracom (Safenet), designed to address the shortcomings of PKCS#11.
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