Simon Willison • 11/25/2025

Constant-time support lands in LLVM: Protecting cryptographic code at the compiler level

Trail of Bits has contributed constant-time support to LLVM 21, introducing new intrinsics like __builtin_ct_select. This prevents optimizing compilers from inadvertently introducing timing vulnerabilities into cryptographic algorithms, providing compiler-level guarantees against branching-related timing attacks.

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#cryptography #Llvm #Compiler Security