Dr Christopher J P Newton

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.

Relay attackers can forward messages between a contactless EMV bank card and a shop reader, making it possible to wirelessly pickpocket money. To protect against this, Apple Pay requires a user's fingerprint or Face ID to authorise payments, while Mastercard and Visa have proposed protocols to stop such relay attacks. We investigate transport payment modes and find that we can build on relaying to bypass the Apple Pay lock screen, and illicitly pay from a locked iPhone to any EMV reader, for any amount, without user authorisation. We show that Visa's proposed relay-countermeasure can be bypassed using rooted smart phones. We analyse Mastercard's relay protection, and show that its timing bounds could be more reliably imposed at the ISO 14443 protocol level, rather than at the EMV protocol level. With these insights, we propose a new relay-resistance protocol (L1RP) for EMV. We use the Tamarin prover to model mobile-phone payments with and without user authentication, and in different payment modes. We formally verify solutions to our attack suggested by Apple and Visa, and used by Samsung, and we verify that our proposed protocol provides protection from relay attacks.

Direct Anonymous Attestation (DAA) is an anonymous signature scheme, which allows the Trusted Platform Module (TPM), a small chip embedded in a host computer, to attest to the state of the host system, while preserving the privacy of the user. DAA provides two signature modes: fully anonymous signatures and pseudonymous signatures. One main goal of designing DAA schemes is to reduce the TPM signing workload as much as possible, as the TPM has only limited resources. In an optimal DAA scheme, the signing workload on the TPM will be no more than that required for a normal signature like ECSchnorr. To date, no scheme has achieved the optimal signing efficiency for both signature modes. In this paper, we propose the first DAA scheme which achieves the optimal TPM signing efficiency for both signature modes. In this scheme, the TPM takes only a single exponentiation to generate a signature, and this single exponentiation can be pre-computed. Our scheme can be implemented using the existing TPM 2.0 commands, and thus is compatible with the TPM 2.0 specification. We benchmarked the TPM 2.0 commands needed for three DAA use cases on an Infineon TPM 2.0 chip, and also implemented the host signing and verification algorithm for our DAA scheme on a laptop with 1.80GHz Intel Core i7-8550U CPU. Our experimental results show that our DAA scheme obtains a total signing time of about 144 ms for either signature mode, while with pre-computation we can obtain a signing time of about 65 ms. Based on our benchmark results for the pseudonymous signature mode, our scheme is roughly 2\times (resp., 5\times ) faster than the existing DAA schemes supported by TPM 2.0 in terms of total (resp., online) signing efficiency.

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.