Injectable RNG for the constant-time EC scalar multipliers - #202
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The constant-time scalar multipliers — the variable-base CT multiplier and the fixed-base comb — drew their scalar blind and projective randomizer from a TSecureRandom they lazily created, bypassing any caller-supplied ISecureRandom. Thread a caller-owned RNG through both so a caller can supply one DRBG for every constant-time multiplication instead of each multiplier instantiating its own. - IECCTMultiplierFactory gains CreateCTMultiplier(ARandom, ABlindBits) and CreateBasePointCTMultiplier(ARandom); the four Fp custom curves implement both. - TEphemeralECDHAgreement and TFpAffineCombMultiplier gain random-accepting constructors. - Key generation and ECDSA signing route the fixed-base blind through their injected RNG. Deterministic signing has no injected RNG, so it keeps the curve's shared multiplier rather than building a fresh DRBG-backed comb per signature. - The injected-RNG entry points reject a nil random instead of silently degrading, and the curve's lazily-cached multipliers are now built under the existing lock. The blind remains transparent to the result (checked against a WNAF reference on secp256r1, secp256k1, secp384r1 and secp521r1), and a counting RNG proves both randomness draws come from the injected source.
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What
The constant-time EC scalar multipliers lazily created their own
TSecureRandomfor the scalar blind and projective-coordinate randomizer, ignoring any
caller-supplied
ISecureRandom. This adds injectable-RNG overloads so a callercan own that randomness with a single DRBG rather than one instantiated per operation.
Changes
IECCTMultiplierFactory:CreateCTMultiplier(const ARandom: ISecureRandom; ABlindBits)(overload) and
CreateBasePointCTMultiplier(const ARandom: ISecureRandom); implemented bythe four Fp custom curves (secp256r1/k1, secp384r1, secp521r1).
TEphemeralECDHAgreementandTFpAffineCombMultiplier: random-accepting constructors.Deterministic (RFC 6979) signing has no injected RNG, so it keeps the curve's cached
multiplier instead of building a fresh DRBG per signature.
lock (pre-existing race on the interface field).
Behaviour
Additive and backward-compatible: the existing non-RNG constructors and factory methods are
unchanged; the blind stays transparent to the result.