Trust and Trustworthy Computing

Direct Anonymous Attestation (DAA) is a cryptographic protocol for privacy-protecting authentication. It is standardized in the TPM standard and implemented in millions of chips. A variant of DAA is also used in Intel’s SGX. Recently, Camenisch et al. (PKC 2016) demonstrated that existing security models for DAA do not correctly capture all security requirements, and showed a number of flaws in existing schemes based on the LRSW assumption. In this work, we identify flaws in security proofs of a number of qSDH-based DAA schemes and point out that none of the proposed schemes can be proven secure in the recent model by Camenisch et al. (PKC 2016). We therefore present a new, provably secure DAA scheme that is based on the qSDH assumption. The new scheme is as efficient as the most efficient existing DAA scheme, with support for DAA extensions to signature-based revocation and attributes. We rigorously prove the scheme secure in the model of Camenisch et al., which we modify to support the extensions. As a side-result of independent interest, we prove that the BBS+ signature scheme is secure in the type-3 pairing setting, allowing for our scheme to be used with the most efficient pairing-friendly curves.