Covert timing channels, caching, and cryptography

Side-channel analysis is a cryptanalytic technique that targets not the formal description of a cryptographic primitive but the implementation of it. Examples of side-channels include power consumption or timing measurements. This is a young but very active field within applied cryptography. Modern processors are equipped with numerous mechanisms to improve the average performance of a program, including but not limited to caches. These mechanisms can often be used as side-channels to attack software implementations of cryptosystems. This area within side-channel analysis is called microarchitecture attacks, and those dealing with caching mechanisms cache-timing attacks. This dissertation presents a number of contributions to the field of side-channel analysis. The introductory portion consists of a review of common cache architectures, a literature survey of covert channels focusing mostly on covert timing channels, and a literature survey of cache-timing attacks, including selective related results that are more generally categorized as side-channel attacks such as traditional timing attacks. This dissertation includes eight publications relating to this field. They contain contributions in areas such as side-channel analysis, data cache-timing attacks, instruction cache-timing attacks, traditional timing attacks, and fault attacks. Fundamental themes also include attack mitigations and efficient yet secure software implementation of cryptosystems. Concrete results include, but are not limited to, four practical side-channel attacks against OpenSSL, each implemented and leading to full key recovery

Secure and Fast Implementations of Two Involution Ciphers

Anubis and Khazad are closely related involution block ciphers. Building on two recent AES software results, this work presents a number of constant-time software implementations of Anubis and Khazad for processors with a byte-vector shuffle instruction, such as those that support SSSE3. For Anubis, the first is serial in the sense that it employs only one cipher instance and is compatible with all standard block cipher modes. Efficiency is largely due to the S-box construction that is simple to realize using a byte shuffler. The equivalent for Khazad runs two parallel instances in counter mode. The second for each cipher is a parallel bit-slice implementation in counter mode

Malware Finances and Operations: a Data-Driven Study of the Value Chain for Infections and Compromised Access

We investigate the criminal market dynamics of infostealer malware and publish three evidence datasets on malware infections and trade. We justify the value chain between illicit enterprises using the datasets, compare the prices and added value, and use the value chain to identify the most effective countermeasures. We begin by examining infostealer malware victim logs shared by actors on hacking forums, and extract victim information and mask sensitive data to protect privacy. We find access to these same victims for sale at Genesis Market. This technically sophisticated marketplace provides its own browser to access victim's online accounts. We collect a second dataset and discover that 91% of prices fall between 1--20 US dollars, with a median of 5 US dollars. Database Market sells access to compromised online accounts. We produce yet another dataset, finding 91% of prices fall between 1--30 US dollars, with a median of 7 US dollars.Comment: In The 18th International Conference on Availability, Reliability and Security (ARES 2023), August 29 -- September 1, 2023, Benevento, Ital

Triggerflow: Regression Testing by Advanced Execution Path Inspection

Cryptographic libraries often feature multiple implementations of primitives to meet both the security needs of handling private information and the performance requirements of modern services when the handled information is public. OpenSSL, the de-facto standard free and open source cryptographic library, includes mechanisms to differentiate the confidential data and its control flow, including runtime flags, designed for hardening against timing side-channels, but repeatedly accidentally mishandled in the past. To analyze and prevent these accidents, we introduce Triggerflow, a tool for tracking execution paths that, assisted by source annotations, dynamically analyzes the binary through the debugger. We validate this approach with case studies demonstrating how adopting our method in the development pipeline would have promptly detected such accidents. We further show-case the value of the tooling by presenting two novel discoveries facilitated by Triggerflow: one leak and one defect

SoK: A Systematic Review of TEE Usage for Developing Trusted Applications

Trusted Execution Environments (TEEs) are a feature of modern central processing units (CPUs) that aim to provide a high assurance, isolated environment in which to run workloads that demand both confidentiality and integrity. Hardware and software components in the CPU isolate workloads, commonly referred to as Trusted Applications (TAs), from the main operating system (OS). This article aims to analyse the TEE ecosystem, determine its usability, and suggest improvements where necessary to make adoption easier. To better understand TEE usage, we gathered academic and practical examples from a total of 223 references. We summarise the literature and provide a publication timeline, along with insights into the evolution of TEE research and deployment. We categorise TAs into major groups and analyse the tools available to developers. Lastly, we evaluate trusted container projects, test performance, and identify the requirements for migrating applications inside them.Comment: In The 18th International Conference on Availability, Reliability and Security (ARES 2023), August 29 -- September 01, 2023, Benevento, Italy. 15 page

Set It and Forget It! Turnkey ECC for Instant Integration

Historically, Elliptic Curve Cryptography (ECC) is an active field of applied cryptography where recent focus is on high speed, constant time, and formally verified implementations. While there are a handful of outliers where all these concepts join and land in real-world deployments, these are generally on a case-by-case basis: e.g.\ a library may feature such X25519 or P-256 code, but not for all curves. In this work, we propose and implement a methodology that fully automates the implementation, testing, and integration of ECC stacks with the above properties. We demonstrate the flexibility and applicability of our methodology by seamlessly integrating into three real-world projects: OpenSSL, Mozilla's NSS, and the GOST OpenSSL Engine, achieving roughly 9.5x, 4.5x, 13.3x, and 3.7x speedup on any given curve for key generation, key agreement, signing, and verifying, respectively. Furthermore, we showcase the efficacy of our testing methodology by uncovering flaws and vulnerabilities in OpenSSL, and a specification-level vulnerability in a Russian standard. Our work bridges the gap between significant applied cryptography research results and deployed software, fully automating the process

OpenSSLNTRU : Faster post-quantum TLS key exchange

Google's CECPQ1 experiment in 2016 integrated a post-quantum key-exchange algorithm, newhope1024, into TLS 1.2. The Google-Cloudflare CECPQ2 experiment in 2019 integrated a more efficient key-exchange algorithm, ntruhrss701, into TLS 1.3. This paper revisits the choices made in CECPQ2, and shows how to achieve higher performance for post-quantum key exchange in TLS 1.3 using a higher-security algorithm, sntrup761. Previous work had indicated that ntruhrss701 key generation was much faster than sntrup761 key generation, but this paper makes sntrup761 key generation much faster by generating a batch of keys at once. Batch key generation is invisible at the TLS protocol layer, but raises software-engineering questions regarding the difficulty of integrating batch key exchange into existing TLS libraries and applications. This paper shows that careful choices of software layers make it easy to integrate fast post-quantum software, including batch key exchange, into TLS with minor changes to TLS libraries and no changes to applications. As a demonstration of feasibility, this paper reports successful integration of its fast sntrup761 library, via a lightly patched OpenSSL, into an unmodified web browser and an unmodified TLS terminator. This paper also reports TLS 1.3 handshake benchmarks, achieving more TLS 1.3 handshakes per second than any software included in OpenSSL.acceptedVersionPeer reviewe

SoK : Remote Power Analysis

In recent years, numerous attacks have appeared that aim to steal secret information from their victim using the power side-channel vector, yet without direct physical access. These attacks are called Remote Power Attacks or Remote Power Analysis, utilizing resources that are natively present inside the victim environment. However, there is no unified definition about the limitations that a power attack requires to be defined as remote. This paper aims to propose a unified definition and concrete threat models to clearly differentiate remote power attacks from non-remote ones. Additionally, we collect the main remote power attacks performed so far from the literature, and the principal proposed countermeasures to avoid them. The search of such countermeasures denoted a clear gap in preventing remote power attacks at the technical level. Thus, the academic community must face an important challenge to avoid this emerging threat, given the clear room for improvement that should be addressed in terms of defense and security of devices that work with private information.acceptedVersionPeer reviewe

A Formula for Disaster : A Unified Approach to Elliptic Curve Special-Point-Based Attacks

The Refined Power Analysis, Zero-Value Point, and Exceptional Procedure attacks introduced side-channel techniques against specific cases of elliptic curve cryptography. The three attacks recover bits of a static ECDH key adaptively, collecting information on whether a certain multiple of the input point was computed. We unify and generalize these attacks in a common framework, and solve the corresponding problem for a broader class of inputs. We also introduce a version of the attack against windowed scalar multiplication methods, recovering the full scalar instead of just a part of it. Finally, we systematically analyze elliptic curve point addition formulas from the Explicit-Formulas Database, classify all non-trivial exceptional points, and find them in new formulas. These results indicate the usefulness of our tooling, which we released publicly, for unrolling formulas and finding special points, and potentially for independent future work.acceptedVersionPeer reviewe

Port Contention for Fun and Profit

Simultaneous Multithreading (SMT) architectures are attractive targets for side-channel enabled attackers, with their inherently broader attack surface that exposes more per physical core microarchitecture components than cross-core attacks. In this work, we explore SMT execution engine sharing as a side-channel leakage source. We target ports to stacks of execution units to create a high-resolution timing side-channel due to port contention, inherently stealthy since it does not depend on the memory subsystem like other cache or TLB based attacks. Implementing said channel on Intel Skylake and Kaby Lake architectures featuring Hyper-Threading, we mount and end-to-end attack that recovers a P-384 private key from an OpenSSL-powered TLS server using a small number of repeated TLS handshake attempts. Furthermore, we show that traces targeting shared libraries, static builds, and SGX enclaves are essentially identical, hence our channel has wide target application