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weierstrass, bls: improve randomPrivateKey security and decrease bias

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This commit is contained in:
Paul Miller 2023-08-11 10:22:37 +00:00
parent ca5583f713
commit 05794c0283
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GPG Key ID: 697079DA6878B89B
2 changed files with 10 additions and 5 deletions
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5
src/abstract/bls.ts
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@ -189,7 +189,10 @@ export function bls<Fp2, Fp6, Fp12>(
const utils = { const utils = {
randomPrivateKey: (): Uint8Array => { randomPrivateKey: (): Uint8Array => {
return Fr.toBytes(hashToPrivateScalar(CURVE.randomBytes(groupLen + 8), CURVE.params.r)); const bytesTaken = groupLen + Math.ceil(groupLen / 2); // e.g. 48b for 32b field
const rand = CURVE.randomBytes(bytesTaken);
const num = hashToPrivateScalar(rand, Fr.ORDER);
return Fr.toBytes(num);
}, },
calcPairingPrecomputes, calcPairingPrecomputes,
}; };

10
src/abstract/weierstrass.ts
View File

@ -845,13 +845,15 @@ export function weierstrass(curveDef: CurveType): CurveFn {
normPrivateKeyToScalar: normPrivateKeyToScalar, normPrivateKeyToScalar: normPrivateKeyToScalar,
/** /**
* Produces cryptographically secure private key from random of size (nBitLength+64) * Produces cryptographically secure private key from random of size
* as per FIPS 186 B.4.1 with modulo bias being neglible. * (groupLen + ceil(groupLen / 2)) with modulo bias being negligible.
*/ */
randomPrivateKey: (): Uint8Array => { randomPrivateKey: (): Uint8Array => {
const rand = CURVE.randomBytes(Fp.BYTES + 8); const groupLen = CURVE.nByteLength;
const bytesTaken = groupLen + Math.ceil(groupLen / 2); // e.g. 48b for 32b field
const rand = CURVE.randomBytes(bytesTaken);
const num = mod.hashToPrivateScalar(rand, CURVE_ORDER); const num = mod.hashToPrivateScalar(rand, CURVE_ORDER);
return ut.numberToBytesBE(num, CURVE.nByteLength); return ut.numberToBytesBE(num, groupLen);
}, },
/** /**