Bringing Zero-Knowledge Proofs of Knowledge to Practice

This paper describes the direct anonymous attestation scheme (DAA). This scheme was adopted by the Trusted Computing Group (TCG) as the method for remote authentication of a hardware module, called Trusted Platform Module (TPM), while preserving the privacy of the user of the platform that contains the module. DAA can be seen as a group signature without the feature that a signature can be opened, i.e., the anonymity is not revocable. Moreover, DAA allows for pseudonyms, i.e., for each signature a user (in agreement with the recipient of the signature) can decide whether or not the signature should be linkable to another signature. DAA furthermore allows for detection of known keys: if the DAA secret keys are extracted from a TPM and published, a verifier can detect that a signature was produced using these secret keys. The scheme is provably secure in the random oracle model under the strong RSA and the decisional Diffie-Hellman assumption.

Direct Anonymous Attestation (DAA) has been adopted in Trusted Platform Module v 1.2 (TPM v1.2) Specification, described by Trusted Computing Group (TCG). It intends to solve the trusted platform attestation and the platform privacy protection. In DAA, the certificate can be used repeatedly and this will provide the opportunities for rogue TPMs to initiate the replay attacks. For identifying the rogue platform, DAA cannot but use a relatively fixed pseudonym rather than a random pseudonym, which would badly weaken the anonymity of the platform. To tackle this problem, a time-and-times-limited strong DAA (TTLS-DAA) scheme, which extends DAA by adding valid period of time and restriction of times into the certificate, is put forward. Since the pseudonym of the user platform is different for each attestation, TTLS-DAA provides stronger anonymity. Being able to control the use of the certificate, it can be widely used in practice especially in commercial fields.

Direct Anonymous Attestation (DAA) is a scheme that enables the remote authentication of a Trusted Platform Module (TPM) while preserving the user's privacy. A TPM can prove to a remote party that it is a valid TPM without revealing its identity and without linkability. In the DAA scheme, a TPM can be revoked only if the DAA private key in the hardware has been extracted and published widely so that verifiers obtain the corrupted private key. If the unlinkability requirement is relaxed, a TPM suspected of being compromised can be revoked even if the private key is not known. However, with the full unlinkability requirement intact, if a TPM has been compromised but its private key has not been distributed to verifiers, the TPM cannot be revoked. Furthermore, a TPM cannot be revoked from the issuer, if the TPM is found to be compromised after the DAA issuing has occurred. In this paper, we present a new DAA scheme called Enhanced Privacy ID (EPID) scheme that addresses the above limitations. While still providing unlinkability, our scheme provides a method to revoke a TPM even if the TPM private key is unknown. This expanded revocation property makes the scheme useful for other applications such as for driver's license. Our EPID scheme is efficient and secure in the same security model as DAA, i.e. in the random oracle model under the strong RSA assumption and the decisional Diffie-Hellman assumption.

Similar to verifiable shuffling (mixing), we consider the problem of verifiable rotating a given list of homomorphic encryptions. The offset by which the list is rotated (cyclic shift) should remain hidden. Basically, we will present zero-knowledge proofs of knowledge of a rotation offset and re-encryption exponents, which define how the input list is transformed into the output list. We also briefly address various applications of verifiable rotation, ranging from `fragile mixing' as introduced by Reiter and Wang at CCS'04 to applications in protocols for secure multiparty computation and voting. We present two new, efficient protocols. Our first protocol is quite elegant and involves the use of the Discrete Fourier Transform (as well as the Fast Fourier Transform algorithm), and works under some reasonable conditions. We believe that this is the first time that Fourier Transforms are used to construct an efficient zero-knowledge proof of knowledge. Our second protocol is more general (requiring no further conditions) and only slightly less efficient than the DFT-based protocol. Unlike the previously best protocol by Reiter and Wang, however, which relies on extensive use of verifiable shuffling as a building block (invoking it four times as a sub-protocol), our construction is direct and its performance is comparable to the performance of a single run of the best protocol for verifiable shuffling.

Trusted Computing (TC) is a technology developed and promoted by the Trusted Computing Group (TCG), and aims to enhance the overall security, privacy and trustworthiness of a variety of computing devices. The core of the trusted computing technologies of TCG is the Trusted Platform Module (TPM), a tamper-resistant module embedded in a platform, which is implemented by a TPM chip and designed to resist software attacks and moderate hardware attacks. TPM includes non-volatile storage, a set of Platform Configuration Registers (PCRs) and an engine for cryptographic operations. Based on TPM and TCG Software Stack (TSS), a suite of mechanisms can be realized, including memory curtaining, protected execution, secure I/O, sealed storage, platform measurement and remote attestation. As a fundamental secure computing module, TPM is the root trust module to establish security and trust in digital computing, communication and networking. Basically, it can support secure booting and trustworthy software installation, private data protection and Digital Rights Management (DRM), as well as remote attestation- based trusted communications and collaboration. There is significant research currently in the field of trusted computing, in both academia and industry. Recent efforts focus on TC module development and extension, trustworthy software assurance, Trusted Execution Environment (TEE), trusted collaboration and trusted storage. The recent advance of Intel Software Guard Extensions (Intel® SGX) offers hardware-assistant TEE, which allows user code execution in a private region of memory, called enclave, in an untrusted third party. This technology attracts special attention and motivates innovations of many applications.

Trusted Platform Module (TPM) is a key component designed to enable computers achieve greater security. Several vulnerabilities discovered in the TPM highlight the necessity of formal analysis. The procedure invoking an API may be regarded as several interactive processes between the TPM and a user. As a result, the current study formalized the API specifications proposed by Trusted Computing Group (TCG) using applied pi calculus. Meanwhile, two authentication properties between them were also described in a formalized way. With the help of the tool ProVerif, the flaw of the command TPM_CertifyKey was discovered. It was also confirmed on the TPM emulator. Subsequently, the modified API was presented and its authentication properties could be satisfied after verifying again. Results show the model is valid. DOI: http://dx.doi.org/10.11591/telkomnika.v11i2.2034

3 - Overview of the TPM Architecture

As the platform mobility increases, it becomes increasingly susceptible to theft. Stolen data is often regarded as being more valuable than the notebook hardware itself. Thus, the need to protect user data and secrets is underscored in a mobile computing environment. The Trusted Platform Module (TPM) is defined as a hardware instantiation which has been proposed by the TCG (Trusted Computing Group) for trust computing. TPM offers facilities for the secure generation of cryptographic keys, and limitations on their use, in addition to a hardware pseudo-random number generator. It also includes capabilities such as remote attestation and sealed storage. A TPM can be used to authenticate hardware devices. Since each TPM chip has a unique and secret RSA key burned in during production, it is capable of performing platform authentication. The TPB (Trusted Platform Board) is an expansion of the TPM for enhancing the efficiency and usability of the TPM chip. In addition to the TPB functions supporting high-standard trust environments within the hardware standard of the system in this paper, we develop the v-TMS (Visual Trustworthy Monitoring System) that provides visualization of real-time monitoring for the behavior of system resources (process, memory, network, users, etc.) with TPB and system software for hardening of OS and applications. Moreover, v-TMS is not only a web-based computing environment for system resources but also a real-time monitoring system for a trust computing environment.

Trusted computing (TC) is considered to be one of the newly developed technologies on improving computer security and creating a trustworthy environment. Although the Trusted Computing Group (TCG) has defined specifications/or TC, including that of trusted platform module (TPM), criteria on compliance testing is still not available. It is important that the design and implementation of TPM and other components follow the specifications, as incompliance may lead to crucial security impacts. In this paper, a test mechanism checking TPM commands is instrumented into TPM application, so that conformance to standards can be examined before TPM's functional execution to validate its compliance with the specifications. Furthermore, this paper also initially puts forward the concept of "chain of compliance", which enhances the trustworthiness of computing platforms by verifying the conformance of their components.

In network-connected UAV (NC-UAV) communication systems, user authentication is replaced by platform identity authentication and integrity check because many NC-UAVs are operated without human intervention. Direct anonymous attestation (DAA) is an attractive cryptographic scheme that provides an elegant balance between platform authentication and anonymity. However, because of the low-level computing capability and limited transmission bandwidth in UAV, the existing DAA schemes are not suitable for NC-UAV communication systems. In this paper, we propose an enhanced DAA scheme with mutual authentication (MA-DAA scheme), which meets the security requirements of NC-UAV communication systems. The proposed MA-DAA scheme, which is based on asymmetric pairings, bundles the identities of trusted platform module (TPM) and Host to solve the malicious module changing attacks. Credential randomization, batch proof and verification, and mutual authentication are realized in the MA-DAA scheme. The computational workload in TPM and Host is reduced in order to meet the low computation and resource requirements in TPM and Host. The entire scheme and protocols are presented, and the security and efficiency of the proposed MA-DAA scheme are proved and analyzed. Our experiment results also confirm the high efficiency of the proposed scheme.

<p>A computer hijacked by a malware may pretend that it is normal as usual and retrieve secrets from storage of itself and other victim computers. By adopting trusted computing technology a computer’s former health status cannot be forged. Computers can thus detect the change of health status of a hijacked computer and prevent the leakage of the secrets. As Trusted Computing Group (TCG) proposed Trusted Platform Module (TPM) specification, IBM implemented software TPM (sTPM) and utilities for engineer who wants to learn the operating principle of TPM. Meanwhile, the blooming of tiny size, but powerful, computers, e.g. Raspberry Pi 2 (Rpi2), attract ones to develop some dedicated applications on the computers. In this article, we report the verified steps for installing new sTPM version on RPi2. After the installation, we also test the functionality and evaluate the performance of the sTPM with some major TPM Commands. The real behaviour of and the traffic between the host computer and the emulated TPM can thus be learned easily.</p>

Direct anonymous attestation (DAA) is an anonymous authentication scheme adopted by the Trusted Computing Group in its specifications for trusted computing platforms. This paper presents an efficient construction that implements all anonymous authentication features specified in DAA, including authentication with total anonymity, authentication with variable anonymity, and rogue TPM tagging. The current DAA construction is mainly targeted for powerful devices such as personal computers, and their corresponding application areas, but is not entirely suitable for embedded devices with limited computing capabilities (e.g., cell phones or hand-held PDAs). We propose a new construction with more efficient sign and verify protocols, making it more attractive for embedded devices. We prove that the new construction is secure under the strong RSA assumption and the decisional Diffie-Hellman assumption.

Cloud computing platforms constructed on Trusted Computing Technology are commonly referred to as trusted cloud computing. The core component of this technology is known as Trusted Platform Module (TPM). Its specifications are given by the consortium known as Trusted Computing Group (TCG). Though TPM is an immovable module and is fixed inside any computer, yet its credentials can be shared with other devices. This paper presents the accessibility model for Virtual Machine (VM) of a distributed trust protocol which is based on TPM, through which consumer's credentials are shared to other trusted devices. These credentials essentially describe the integrity of VM.

: The design of a trusted system based on the Trusted Computing Group's Trusted Platform Module (TPM) was analyzed to understand the role and trust relationships of the TPM, firmware, and software modules involved. The objective was to confirm that the measurements stored and reported by the TPM can successfully discriminate a normal boot sequence, which leaves trusted system software in control, from an insecure one, where some trusted modules might have been replaced by malicious ones. The principal tool used in the analysis was the SMV symbolic model checker.

To prevent unauthorized access to protected trusted platform module (TPM) objects, authorization protocols, such as the object-specific authorization protocol (OSAP), have been introduced by the trusted computing group (TCG). By using OSAP, processes trying to gain access to the protected TPM objects need to prove their knowledge of relevant authorization data before access to the objects can be granted. Chen and Ryan's 2009 analysis has demonstrated OSAP's authentication vulnerability in sessions with shared authorization data. They also proposed the Session Key Authorization Protocol (SKAP) with fewer stages as an alternative to OSAP. Chen and Ryan's analysis of SKAP using ProVerif proves the authentication property. The purpose of this paper was to examine the usefulness of Colored Petri Nets (CPN) and CPN Tools for security analysis. Using OSAP and SKAP as case studies, we construct intruder and authentication property models in CPN. CPN Tools is used to verify the authentication property using a Dolev---Yao-based model. Verification of the authentication property in both models using the state space tool produces results consistent with those of Chen and Ryan.