TALUS: Reinforcing TEE Confidentiality with Cryptographic Coprocessors (Technical Report)

Platforms are nowadays typically equipped with tristed execution environments (TEES), such as Intel SGX and ARM TrustZone. However, recent microarchitectural attacks on TEEs repeatedly broke their confidentiality guarantees, including the leakage of long-term cryptographic secrets. These systems are typically also equipped with a cryptographic coprocessor, such as a TPM or Google Titan. These coprocessors offer a unique set of security features focused on safeguarding cryptographic secrets. Still, despite their simultaneous availability, the integration between these technologies is practically nonexistent, which prevents them from benefitting from each other's strengths. In this paper, we propose TALUS, a general design and a set of three main requirements for a secure symbiosis between TEEs and cryptographic coprocessors. We implement a proof-of-concept of TALUS based on Intel SGX and a hardware TPM. We show that with TALUS, the long-term secrets used in the SGX life cycle can be moved to the TPM. We demonstrate that our design is robust even in the presence of transient execution attacks, preventing an entire class of attacks due to the reduced attack surface on the shared hardware.Comment: In proceedings of Financial Cryptography 2023. This is the technical report of the published pape

Type-Based Analysis of Protected Storage in the TPM (full version)

The Trusted Platform Module (TPM) is designed to enable trustworthy computation and communication over open networks. The TPM provides a way to store cryptographic keys and other sensitive values in its shielded memory and act as \emph{Root of Trust for Storage} (RTS). The TPM interacts with applications via a predefined set of commands (an API). In this paper, we give an abstraction model for the TPM 2.0 specification concentrating on Protected Storage part. With identification and formalization of their secrecy properties, we devise a type system with asymmetric cryptographic primitives to statically enforce and prove their security

Security and trust in a Network Functions Virtualisation Infrastructure

L'abstract è presente nell'allegato / the abstract is in the attachmen

Proving Cryptographic C Programs Secure with General-Purpose Verification Tools

Security protocols, such as TLS or Kerberos, and security devices such as the Trusted Platform Module (TPM), Hardware Security Modules (HSMs) or PKCS#11 tokens, are central to many computer interactions. Yet, such security critical components are still often found vulnerable to attack after their deployment, either because the specification is insecure, or because of implementation errors. Techniques exist to construct machine-checked proofs of security properties for abstract specifications. However, this may leave the final executable code, often written in lower level languages such as C, vulnerable both to logical errors, and low-level flaws. Recent work on verifying security properties of C code is often based on soundly extracting, from C programs, protocol models on which security properties can be proved. However, in such methods, any change in the C code, however trivial, may require one to perform a new and complex security proof. Our goal is therefore to develop or identify a framework in which security properties of cryptographic systems can be formally proved, and that can also be used to soundly verify, using existing general-purpose tools, that a C program shares the same security properties. We argue that the current state of general-purpose verification tools for the C language, as well as for functional languages, is sufficient to achieve this goal, and illustrate our argument by developing two verification frameworks around the VCC verifier. In the symbolic model, we illustrate our method by proving authentication and weak secrecy for implementations of several network security protocols. In the computational model, we illustrate our method by proving authentication and strong secrecy properties for an exemplary key management API, inspired by the TPM

Car-to-Smartphone Interactions: Experimental Setup, Risk Analysis and Security Technologies

International audienceVehicle access control and in particular access to in-vehicle functionalities from smart mobile devices, e.g., phones or watches, has become an increasingly relevant topic. Security plays a critical part, due to both a long history of car keys that succumbed to attacks and recently reported intrusions that use various vehicle communication interfaces to further gain access to in-vehicle safety-critical components. In this work we discuss existing technologies and functionalities that should be embedded in an experimental setup that addresses such a scenario. We make emphasis on existing cryptographic technologies, from symmetric to asymmetric primitives, identity-based cryptography and group signatures. We also discuss risks associated with in-vehicle functionalities and mitigation, e.g., intrusion detection systems

TALUS: Reinforcing TEE Confidentiality with Cryptographic Coprocessors

Platforms are nowadays typically equipped with trusted execution environments (TEEs), such as Intel SGX or ARM TrustZone. However, recent microarchitectural attacks on TEEs repeatedly broke their confidentiality guarantees, including the leakage of long-term cryptographic secrets. These systems are typically also equipped with a cryptographic coprocessor, such as a TPM or Google Titan. These coprocessors offer a unique set of security features focused on safeguarding cryptographic secrets. Still, despite their simultaneous availability, the integration between these technologies is practically nonexistent, which prevents them from benefitting from each other’s strengths. In this paper, we propose TALUS , a general design and a set of three main requirements for a secure symbiosis between TEEs and cryptographic coprocessors. We implement a proof-of-concept of TALUS based on Intel SGX and a hardware TPM. We show that with TALUS, the long-term secrets used in the SGX life cycle can be moved to the TPM. We demonstrate that our design is robust even in the presence of transient execution attacks, preventing an entire class of attacks due to the reduced attack surface on the shared hardware

Trusted execution: applications and verification

Useful security properties arise from sealing data to specific units of code. Modern processors featuring Intel’s TXT and AMD’s SVM achieve this by a process of measured and trusted execution. Only code which has the correct measurement can access the data, and this code runs in an environment trusted from observation and interference. We discuss the history of attempts to provide security for hardware platforms, and review the literature in the field. We propose some applications which would benefit from use of trusted execution, and discuss functionality enabled by trusted execution. We present in more detail a novel variation on Diffie-Hellman key exchange which removes some reliance on random number generation. We present a modelling language with primitives for trusted execution, along with its semantics. We characterise an attacker who has access to all the capabilities of the hardware. In order to achieve automatic analysis of systems using trusted execution without attempting to search a potentially infinite state space, we define transformations that reduce the number of times the attacker needs to use trusted execution to a pre-determined bound. Given reasonable assumptions we prove the soundness of the transformation: no secrecy attacks are lost by applying it. We then describe using the StatVerif extensions to ProVerif to model the bounded invocations of trusted execution. We show the analysis of realistic systems, for which we provide case studies

Security and Trust in Safety Critical Infrastructures

Critical infrastructures such as road vehicles and railways are undergoing a major change, which increases the dependency of their operation and control on Information Technology (IT) and makes them more vulnerable to malicious intent. New complex communication infrastructures emerge using the increased connectivity of these safety-critical systems to enable efficient management of operational processes, service provisioning, and information exchange for various (third-party) actors. Railway Command and Control Systems (CCSs) turn with the introduction of digital interlocking into an “Internet of Railway Things”, where safety-critical railway signaling components are deployed on common-purpose platforms and connected via standard IP-based networks. Similarly, the mass adoption of Electric Vehicles (EVs) and the need to supply their batteries with energy for charging has given rise to a Vehicle-to-Grid (V2G) infrastructure, which connects vehicles to power grids and multiple service providers to coordinate charging and discharging processes and maintain grid stability under varying power demands. The Plug-and-Charge feature brought in by the V2G communication standard ISO 15118 allows an EV to access charging and value-added services, negotiate charging schedules, and support the grid as a distributed energy resource in a largely automated way, by leveraging identity credentials installed in the vehicle for authentication and payment. The fast deployment of this advanced functionality is driven by economical and political decisions including the EU Green Deal for climate neutrality. Due to the complex requirements and long standardization and development cycles, the standards and regulations, which play the key role in operating and protecting critical infrastructures, are under pressure to enable the timely and cost-effective adoption. In this thesis, we investigate security and safety of future V2G and railway command and control systems with respect to secure communication, platform assurance as well as safety and security co-engineering. One of the major goals in this context is the continuous collaboration and establishment of the proposed security solutions in upcoming domain-specific standards, thus ensuring their practical applicability and prompt implementation in real-world products. We first analyze the security of V2G communication protocols and requirements for secure service provisioning via charging connections. We propose a new Plug-and-Patch protocol that enables secure update of EVs as a value-added service integrated into the V2G charging loop. Since EVs can also participate in energy trading by storing and feeding previously stored energy to grid, home, or other vehicles, we then investigate fraud detection methods that can be employed to identify manipulations and misbehaving users. In order to provide a strong security foundation for V2G communications, we propose and analyze three security architectures employing a hardware trust anchor to enable trust establishment in V2G communications. We integrate these architectures into standard V2G protocols for load management, e-mobility services and value-added services in the V2G infrastructure, and evaluate the associated performance and security trade-offs. The final aspect of this work is safety and security co-engineering, i.e., integration of safety and security processes vital for the adequate protection of connected safety-critical systems. We consider two application scenarios, Electric Vehicle Charging System (EVCS) and Object Controller (OC) in railway CCS, and investigate how security methods like trusted computing can be applied to provide both required safety and security properties. In the case of EVCS, we bind the trust boundary for safety functionality (certified configuration) to the trust boundary in the security domain and design a new security architecture that enforces safety properties via security assertions. For the railway use case, we focus on ensuring non-interference (separation) between these two domains and develop a security architecture that allows secure co-existence of applications with different criticality on the same hardware platform. The proposed solutions have been presented to the committee ISO/TC 22/SC 31/JWG 1 that develops the ISO 15118 standard series and to the DKE working group “Informationssicherheit für Elektromobilität” responsible for the respective application guidelines. Our security extension has been integrated in the newest edition ISO 15118-20 released in April 2022. Several manufacturers have already started concept validation for their future products using our results. In this way, the presented analyses and techniques are fundamental contributions in improving the state of security for e-mobility and railway applications, and the overall resilience of safety-critical infrastructures to malicious attacks

Engineering Trustworthy Systems by Minimizing and Strengthening their TCBs using Trusted Computing

The Trusted Computing Base (TCB) describes the part of an IT system that is responsible for enforcing a certain security property of the system. In order to engineer a trustworthy system, the TCB must be as secure as possible. This can be achieved by reducing the number, size and complexity of components that are part of the TCB and by using hardened components as part of the TCB. Worst case scenario is for the TCB to span the complete IT system. Best case is for the TCB to be reduced to only a strengthened Root of Trust such as a Hardware Security Module (HSM). One such very secure HSMs with many capabilities is the Trusted Platform Module (TPM). This thesis demonstrates how the TCB of a system can be largely or even solely reduced to the TPM for a variety of security policies, especially in the embedded domain. The examined scenarios include the policies for securing of device resident data at rest also during firmware updates, the enforcement of firmware product lines at runtime, the securing of payment credentials in Plug and Charge controllers, the recording of audit trails over attestation data and a very generic role-based access management. In order to allow evaluating these different solutions, the notion of a dynamic lifecycle dimension for a TCB is introduced. Furthermore, an approach towards engineering such systems based on a formal framework is presented. These scenarios provide evidence for the potential to enforce even complex security policies in small and thus strong TCBs. The approach for implementing those policies can often be inspired by a formal methods based engineering process or by means of additive functional engineering, where a base system is expanded by increased functionality in each step. In either case, a trustworthy system with high assurance capabilities can be achieved