Multiple timing variability issues in operations intended to be constant-time

## Summary Several operations intended to be constant-time could execute secret-dependent branches, depending on the compiler and target CPU. These include subtraction, zero counting, division, and Montgomery multiplication. Additionally, `UintRef` equality could terminate at the first unequal limb, and `BoxedMontyForm::invert` branched on whether an inverse exists. ## Impact Applications using affected operations on secret integers may leak information through timing or microarchitectural side channels. This includes information about intermediate arithmetic values, matching limbs, and invertibility. Such leakage could potentially enable recovery of cryptographic secrets. Practical exploitability depends on the downstream algorithm, compiler, target CPU, and an attacker's ability to observe the side channel. ## Resolution Upgrade to v0.7.6, which removes the identified branches, updates `ctutils` to include its constant-time fixes, and adds BINSEC-based regression checks using `cargo checkct` for arithmetic on multiple targets.

Source published

23 Oct 2026 12:00:00 UTC

Source modified

24 Oct 2026 03:45:02 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

OSV · upstream source license applies

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