FaCT: A Flexible, Constant-Time Programming Language

We argue that C is unsuitable for writing timingchannel free cryptographic code that is both fast and readable. Readable implementations of crypto routines would contain highlevel constructs like if statements, constructs that also introduce timing vulnerabilities. To avoid vulnerabilities, programmers must rewrite their code to dodge intuitive yet dangerous constructs, cluttering the codebase and potentially introducing new errors. Moreover, even when programmers are diligent, compiler optimization passes may still introduce branches and other sources of timing side channels. This status quo is the worst of both worlds: tortured source code that can still yield vulnerable machine code. We propose to solve this problem with a domainspecific language that permits programmers to intuitively express crypto routines and reason about secret values, and a compiler that generates efficient, timing-channel free assembly code.