Constant-time review › sign-25 · Report

Constant-time review — 25 SQIsign2D2

Scope: reference implementation, representative instance only: Implementations/Reference_Implementation/SQISign2Dsquare-Level2-sec/sqisign/sign.c. Other instances and optimized implementations have not been proven source-equivalent. This is a source-level triage, not a constant-time certification.

Secret: ideal/isogeny trapdoor, signing randomness and intermediate quaternion/curve values. Public: verification key, challenge and final signature.

• Branch/loop trace: Implementations/Reference_Implementation/SQISign2Dsquare-Level2-sec/sqisign/sign.c:253 — A search loop exits when found becomes true during isogeny response construction; secret ideal inputs reach this path, but no observable secret-dependent value is yet isolated.
• Table lookups and division/remainder: this source triage does not certify their absence or constant-time compilation. Only the explicitly traced operands above are classified. Public lengths, fixed parameters and verifier checks are not findings.

Assessment: No new vulnerability report is promoted from this representative source triage. A compiler/architecture-specific timing and cache test is still needed before claiming constant-time behavior or exploitable leakage.

Recheck the cited source line and its caller before reusing this result. A timing claim requires controlled same-public-input tests with changed secret state and a public-value control.