Direct Anonymous Attestation (Daa) is a set of cryptographic schemes used to create anonymous digital signatures. To provide additional assurance, Daa schemes can utilise a Trusted Platform Module (Tpm) that is a tamper-resistant hardware device embedded in a computing platform and which provides cryptographic primitives and secure storage. We extend Chen and Li’s Daa scheme to support: 1) signing a message anonymously, 2) self-certifying Tpm keys, and 3) ascertaining a platform’s state as recorded by the Tpm’s platform configuration registers (PCR) for remote attestation, with explicit reference to Tpm 2.0 API calls.We perform a formal analysis of the scheme and are the first symbolic models to explicitly include the low-level Tpm call details. Our analysis reveals that a fix proposed by Whitefield et al. to address an authentication attack on an Ecc-Daa scheme is also required by our scheme. Developing a finegrained, formal model of a Daa scheme contributes to the growing body of work demonstrating the use of formal tools in supporting security analyses of cryptographic protocols. We additionally provide and benchmark an open-source C++ implementation of this Daa scheme supporting both a hardware and a software Tpm and measure its performance.
Passwords are the de facto standard for authentication despite their significant weaknesses. While businesses are currently focused on implementing multi-factor authentication to provide greater security, user adoption is still low. An alternative, WebAuthn, uses cryptographic key pairs to provide password-less authentication. WebAuthn has been standardised and is resilient to phishing attacks. However, its adoption is also very low; the barriers to adoption include usability and resilience of keys. We propose a novel architecture for password-less authentication designed to improve usability and deployability. Our architecture is based on the WebAuthn standards and supports registration and login to web-services. We support a WebAuthn authenticator that generates and uses the key pairs on the client device by providing resilience for these key pairs by using a backup key store in the cloud. We also propose a WebAuthn authenticator using a key store in the cloud so that password-less authentication can be used interoperably between devices. We also assess the properties of these architectures against identified threats and how they can form the basis for improving usability and lowering the technical barriers to adoption of password-less authentication.