Anonymity and pseudonymity are important concepts in the domain of the Internet of Things. The existing privacy-preserving key agreement schemes are only concerned with maintaining the privacy of the communicated data that appears on the channel established between two honest entities. However, privacy should also include anonymity or pseudonymity of the device identity. This means there should not exist any correlation handle to associate different communications done by the device.

Anonymous credential schemes are commonly used to implement privacy-preserving cryptographic protocols. While Trusted Computing platforms are used to establish trust within a network. In this paper we show how a recently proposed Anonymous Authenticated Credential Key Agreement scheme (AACKA) can be used with a off-the-shelf TPM and what is necessary for it. We also introduce promising TPM-related use cases where the AACKA protocol can be applied. Finally, we evaluate the implementation with a hardware TPM and propose extensions for a standard TPM2.0 in order to enhance security.

Anonymous credential schemes based on elliptic curve pairings are often used to implement privacy-friendly cryptographic protocols, with Direct Anonymous Attestation and Enhanced Privacy IDentification being the most prominent anonymous credential schemes. However, all those schemes are signature-based and do not immediately provide for agreement of (symmetric) encryption keys.In this paper we present a scheme for Anonymous Authenticated Credential Key Agreement, which can be used in anonymously authenticated encryption schemes. This novel building-block combines Camenisch-Lysyanskaya credentials with elliptic curve Diffie-Hellman key agreement.We show how the Authenticated Anonymous Key Agreement protocol can be used to design an anonymous credential based Elliptic Curve Integrated Encryption scheme and argue that it is more efficient than conventional hybrid approaches. We show the applicability of our scheme on performance-restricted Internet of Things devices in Cloud-, Fog-, or Edge-Computing scenarios. In particular, we provide an implementation and a performance evaluation for a standard-compliant Java Card 3.1 device.

The Trusted Platform Module (TPM) is an international standard for a security chip that can be used for the management of cryptographic keys and for remote attestation. The specification of the most recent TPM 2.0 interfaces for direct anonymous attestation unfortunately has a number of severe shortcomings. First of all, they do not allow for security proofs (indeed, the published proofs are incorrect). Second, they provide a Diffie-Hellman oracle w.r.t. the secret key of the TPM, weakening the security and preventing forward anonymity of attestations. Fixes to these problems have been proposed, but they create new issues: they enable a fraudulent TPM to encode information into an attestation signature, which could be used to break anonymity or to leak the secret key. Furthermore, all proposed ways to remove the Diffie-Hellman oracle either strongly limit the functionality of the TPM or would require significant changes to the TPM 2.0 interfaces. In this paper we provide a better specification of the TPM 2.0 interfaces that addresses these problems and requires only minimal changes to the current TPM 2.0 commands. We then show how to use the revised interfaces to build q-SDH-and LRSW-based anonymous attestation schemes, and prove their security. We finally discuss how to obtain other schemes addressing different use cases such as key-binding for U-Prove and e-cash.