Constant-time review › kem-28

Constant-time review — kem-28 OAEP-NTRU

Scope: representative reference instance Implementations/Reference_Implementation/OAEP-NTRU-648/KEM_AlgorithmInstance.c; other levels, optimized copies and compiled machine code are not certified by this source review.

Secret-bearing values: private decapsulation key, recovered message/error state, rejection secret and shared secret. Public values: public key, ciphertext and encoded lengths. A decoder result is not automatically public merely because its ciphertext input is public.

• Source trace: Implementations/Reference_Implementation/OAEP-NTRU-648/KEM_AlgorithmInstance.c:190 — The decapsulation accumulator incorporates private decryption/check results and is returned as fail at line 209; the API already exposes this validity result.
• Branches, indexed accesses and division/remainder: this first pass classifies only the traced operand above. Public-seed rejection and fixed-divisor arithmetic are not treated as leaks; absence of other leaks has not been proved.

Assessment: No new side-channel report is promoted from this representative path. Lower-level decoding, sampling and compiler output remain open audit work.

Reproduction is source/dataflow inspection at the cited location. A remote timing claim needs repeated same-public-input tests with changed secret state and an independent public-value control.