CVE-2026-18036

CVE-2026-18036 · NTRU leaks private key information by reducing secret values with a non-constant-time integer division

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In Bouncy Castle for Java before 1.86, NTRU reduced secret values with the % operator in three helpers whose reference implementations are deliberately division-free, so each reduction was carried out by an integer division whose latency depends on the secret operand. Polynomial.modQ divided by a variable divisor, which a compiler cannot strength-reduce to a multiply the way it can a constant one, so it emitted a division on every call including on the decapsulation path where the dividend derives from the private key; Polynomial.mod3 and NTRUSampling.mod3 divided the secret key polynomials f and g during key generation, the message polynomials r and m during encapsulation, and coefficients recovered during decapsulation. An attacker able to measure that timing can recover information about the NTRU private key. modQ now masks, which is exact because q is always a power of two, and mod3 uses the reference implementation's division-free fold and select; the results are unchanged.

CVSS 8.2 · Élevée · EPSS 0,3% · Correctif disponible

Publication

2026-10-02T07:54:16.063Z

Mise à jour

2026-10-02T17:42:56.393Z

Pile logicielle: system

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