Paper 2024/1323

SoK: Instruction Set Extensions for Cryptographers

Abstract

Framed within the general context of cyber-security, standard cryptographic constructions often represent an enabling technology for associated solutions. Alongside or in combination with their design, therefore, the implementation of such constructions is an important challenge: beyond delivering artefacts that are usable in practice, implementation can impact many quality metrics (such as efficiency and security) which determine fitness-for-purpose. A rich design space of implementation techniques can be drawn on in order to address this challenge, but threat- and opportunity-driven innovation based on clear understanding and empirical evidence remains vital. In at least some use-cases, software-based implementation of cryptography is important, e.g., because it delivers an attractive trade off or is mandated for some reason. Such an implementation is heavily influenced both by 1) the Instruction Set Architecture (ISA) it is expressed using, and 2) the micro-architecture it is executed using. For example, the extent to which a general-purpose ISA can support more domain-specific requirements of a cryptographic construction will influence how the latter is mapped to the former (i.e., which implementation techniques are viable) and behavioural properties of doing so (e.g., the execution latency stemming from use of a given implementation technique). This paper attempts to systematise the topic of cryptographic Instruction Set Extensions (ISEs), which represent an approach to provision of a platform where such support is more explicit and extensive. At a high level, the goal is to improve understanding of what is an extensive and somewhat inter-disciplinary body of literature (e.g., spanning academia and industry, hardware and software, as well as cryptographic and non-cryptographic publication venues). We argue that doing so will help to maximise the quality of subsequent work on this and associated topics.