Ruhr-Universität Bochum (RUB): Open Journal Systems
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Designing a General-Purpose 8-bit (T)FHE Processor Abstraction
Get PDFMaking the most of TFHE programmable bootstrapping to evaluate functions or operators otherwise challenging to perform with only the native addition and multiplication of the scheme is a very active line of research. In this paper, we systematize this approach and apply it to build an 8-bit FHE processor abstraction, i.e., a software entity that works over FHE-encrypted 8-bit data and presents itself to the programmer by means of a conventional-looking assembly instruction set. In doing so, we provide several homomorphic LookUp Table (LUT) dereferencing operators based on variants of the tree-based method and show that they are the most efficient option for manipulating encryptions of 8-bit data (optimally represented as two basis 16 digits). We then systematically apply this approach over a set of around 50 instructions, including, notably, conditional assignments, divisions, or fixed-point arithmetic operations. We further test the approach on several simple algorithms, including the execution of a neuron with a sigmoid activation function with 16-bit precision. We conclude the paper by comparing our work to the FHE compilers available in the state of the art. Finally, this work reveals that a very limited set of functional bootstrapping patterns is versatile and efficient enough to achieve general-purpose FHE computations beyond the boolean circuit approach. As such, these patterns may be an appropriate target for further works on advanced software optimizations or hardware implementations
Skyscraper: Fast Hashing on Big Primes
Get PDFArithmetic hash functions defined over prime fields have been actively developed and used in verifiable computation (VC) protocols. Among those, ellipticcurve- based SNARKs require large (256-bit and higher) primes. Such hash functions are notably slow, losing a factor of up to 1000 compared to regular constructions like SHA-2/3.In this paper, we present the hash function Skyscraper, which is aimed at large prime fields and provides major improvements compared to Reinforced Concrete and Monolith. First, the design is exactly the same for all large primes, which simplifies analysis and deployment. Secondly, it achieves a performance comparable to cryptographic hash standards by using low-degree non-invertible transformations and minimizing modulo reductions. Concretely, it hashes two 256-bit prime field (BLS12-381 curve scalar field) elements in 135 nanoseconds, whereas SHA-256 needs 42 nanoseconds on the same machine.The low circuit complexity of Skyscraper, together with its high native speed, should allow a substantial reduction in many VC scenarios, particularly in recursive proofs
Tailorable codes for lattice-based KEMs with applications to compact ML-KEM instantiations
Get PDFCompared to elliptic curve cryptography, a primary drawback of latticebased schemes is the larger size of their public keys and ciphertexts. A common procedure for compressing these objects consists essentially of dropping some of their least significant bits. Albeit effective for compression, there is a limit to the number of bits to be dropped before we get a noticeable decryption failure rate (DFR), which is a security concern. To address this issue, this paper presents a family of error-correction codes that, by allowing an increased number of dropped bits while preserving a negligible DFR, can be used for both ciphertext and publickey compression in modern lattice-based schemes. To showcase the impact and practicality of our proposal, we use the highly optimized ML-KEM, a post-quantum lattice-based scheme recently standardized by NIST. We provide detailed procedures for tailoring our codes to ML-KEM’s specific noise distributions, and show how to analyze the DFR without independence assumptions on the noise coefficients. Among our results, we achieve between 4% and 8% ciphertext compression for MLKEM. Alternatively, we obtain 8% shorter public keys compared to the current standard. We also present isochronous implementations of the decoding procedure, achieving negligible performance impact in the full ML-KEM decapsulation even when considering optimized implementations for AVX2, Cortex-M4, and Cortex-A53
The information-processing perspective on representation
Get PDFI introduce a novel framework for theorizing about representations in cognitive science, which relies on two theses. First, representations are, primarily, signals for information transmission, not as a side effect of other functions these signals may have, but for its own sake. Second, these signals aim at efficiently trading-off three cognitive budgets: rate (or transmission and storage costs), distortion (or faithfulness of the transmitted information), and computational complexity of coders. The way to provide empirical evidence that some entity is a representation—and hence that it is involved in information transmission for the sake of information transmission, as per the first thesis—is to show that it present adaptations for efficient information transmission—as per the second thesis. The kinds of properties that cognitive scientists routinely associate with paradigmatic instances of representations are generated by adaptations for rate-distortion-complexity efficiency
The promise and perils of moral enhancement with neurotechnology
Get PDFJoshua May’s Neuroethics: Agency in the Age of Brain Science is a landmark achievement in the field. I discuss May’s chapter on the topic of moral enhancement. May examines whether it is morally permissible to go beyond treatment and enhance our moral capacities and character via direct brain interventions. May argues for a permissive stance in which the safe experimentation by individuals of some currently available forms of direct brain interventions are permissible. I contend that May’s discussion overlooks some central distinctions and arguments in the literature on moral enhancement. Specifically, I argue that the discussion would benefit from: a closer look at the Bioethics literature on the treatment/enhancement distinction, the relevant sense of ‘moral’ in this debate, arguments in favor of a moral duty to develop and widely deploy neurotechnologies that could be used for moral enhancement, and examining how radical enhancements, transhumanism and moral status issues are central to the topic
Diversifying Learning Goals in Philosophy Education: A Report From the Netherlands
Get PDFThis article examines how the curricular anchor points outlined in the Dutch Scientific Curriculum Commission\u27s 2021 study, Kaders voor kansen [A Framework for Equal Opportunity], can be applied to the philosophy curriculum in secondary schools. The analysis is informed by the findings of the professional learning community Adding Voices to the Philosophy Curriculum at ICLON, Leiden University Graduate School of Teaching. Using the learning goals architecture developed by the Netherlands Institute for Curriculum Development, the paper offers several examples of learning goals that demonstrate strategies for diversifying the curriculum
Review: Franke, Manuela; Lachmund, Anne-Marie (2024): Digitales Lesen im Fremdsprachenunterricht.
No full textRezension: Franke, Manuela; Lachmund, Anne-Marie (2024): Digitales Lesen im Fremdsprachenunterricht. Review: Franke, Manuela; Lachmund, Anne-Marie (2024): Digitales Lesen im Fremdsprachenunterricht.  
Talk: Blurring Enclave Page Accesses in Space and Time with Compile-Time Instrumentation
Get PDFThis talk overviews our recent work on TLBlur, a novel approach that leverages compiler instrumentation and the recent AEX-Notify hardware extension in modern, off-the-shelf Intel SGX processors to limit the bandwidth of controlled-channel attacks at acceptable performance overhead. We also discuss ongoing efforts to reduce instrumentation costs through binary layout optimizations
Hidden in Plain Sight: Scriptless Microarchitectural Attacks via TrueType Font Hinting
Get PDFMicroarchitectural attacks threaten system security and privacy, especially if they can be mounted without native code execution. Recent research has shown that such attacks are possible from within web browsers via JavaScript and WebAssembly. Moreover, recent works have demonstrated that "scriptless" attacks, using only CSS, can be leveraged for side-channel attacks, including cache contention and user fingerprinting.
In this paper, we introduce a new class of scriptless attacks that use the hinting instructions embedded within TrueType font files. We show that the hinting language is sufficiently robust to craft cache attacks, demonstrating cache-contention attacks and precise L1 Prime+Probe attacks. We demonstrate a website fingerprinting attack, as well as a method to track which page of a PDF is currently displayed. Our results demonstrate the practicality of font-based scriptless attacks in real-world scenarios. This emphasizes the need for future mitigations that go beyond traditional scripting languages
Talk: Transient-execution attacks on the CHERI Morello platform
Get PDFCHERI (Capability Hardware Enhanced RISC Instructions) is a capability-based ISA extension providing spatial memory protection and compartmentalisation. CHERI capabilities show a lot of promise in securing computer systems from common access control and memory safety exploits, but as CHERI implementations continue to mature it is important to consider other attack vectors.
One class of attacks that become relevant with the introduction of superscalar and out-of-order CHERI-based processors are transient-execution attacks such as Spectre and Meltdown. Given the ISA overhaul required when porting any given architecture to a CHERI model, these changes will necessarily affect the efficacy of these microarchitectural attacks. This is particularly apparent when looking at design decisions such as how and when capabilities are invalidated in the speculative path, or what triggers an exception as opposed to simply making the capability invalid. Reproducing these attacks is the first step, as new architectural primitives also opens the door for new CHERI-specific microarchitectural exploits that bypass protection model guarantees.
Our current work involves exploring what CHERI does to both mitigate and exacerbate transient-execution attacks, focussing on the Arm Morello prototype implementation of the CHERI ISA to ARMv8-A. The talk will cover porting the Spectre-PHT and Spectre-BTB attacks to CheriBSD, an operating system designed to take full advantage of CHERI\u27s protection model. We will discuss current Arm Morello test results about how changes to capability metadata such as bounds, addresses, and permissions behave in the speculative path - in particular, how good practice that makes full use of capabilities protects systems from Spectre-style vulnerabilities. Design considerations unique to not only the CHERI model but to the OS and compiler will also be demonstrated, such as compiling in hybrid vs \u27purecap\u27 mode, and compiler options determining how capability bounds are set