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Speed Up signatures and strengthen verifications #47

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Speed Up signatures and strengthen verifications #47

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21 changes: 15 additions & 6 deletions src/ecdsa.js
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Original file line number Diff line number Diff line change
Expand Up @@ -68,7 +68,7 @@ function sign(curve, hash, d, nonce) {
var n = curve.n
var G = curve.G

var r, s
var r, s, RyPar
var k = deterministicGenerateK(curve, hash, d, function (k) {
// find canonically valid signature
var Q = G.multiply(k)
Expand All @@ -77,6 +77,7 @@ function sign(curve, hash, d, nonce) {

r = Q.affineX.mod(n)
if (r.signum() === 0) return false
RyPar = Q.affineY.testBit(0)

s = k.modInverse(n).multiply(e.add(d.multiply(r))).mod(n)
if (s.signum() === 0) return false
Expand All @@ -87,14 +88,19 @@ function sign(curve, hash, d, nonce) {
var N_OVER_TWO = n.shiftRight(1)

// enforce low S values, see bip62: 'low s values in signatures'
var sigparity
if (s.compareTo(N_OVER_TWO) > 0) {
s = n.subtract(s)
sigparity = RyPar ? 0 : 1
}
else {
sigparity = RyPar ? 1 : 0
}

return ECSignature(r, s)
return ([ECSignature(r, s), sigparity])
}

function verifyRaw(curve, e, signature, Q) {
function verifyRaw(curve, e, signature, Q, Rypar) {
var n = curve.n
var G = curve.G

Expand Down Expand Up @@ -125,15 +131,18 @@ function verifyRaw(curve, e, signature, Q) {
// 1.4.7 Set v = xR mod n
var v = xR.mod(n)

// Extract R.y parity
var RyParComputed = R.affineY.testBit(0) ? 1 : 0

// 1.4.8 If v = r, output "valid", and if v != r, output "invalid"
return v.equals(r)
return v.equals(r) && RyParComputed === Rypar
}

function verify(curve, hash, signature, Q) {
function verify(curve, hash, signature, Q, Rpar) {
// 1.4.2 H = Hash(M), already done by the user
// 1.4.3 e = H
var e = BigInteger.fromBuffer(hash)
return verifyRaw(curve, e, signature, Q)
return verifyRaw(curve, e, signature, Q, Rpar-31)
}

/**
Expand Down
9 changes: 5 additions & 4 deletions src/signature.js
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Original file line number Diff line number Diff line change
Expand Up @@ -54,7 +54,8 @@ function Signature(r, s, i) {
return ecdsa.verify(
curve, dataSha256,
{ r: r, s: s },
publicKey.Q
publicKey.Q,
i
);
};

Expand Down Expand Up @@ -202,17 +203,17 @@ Signature.signHash = function(dataSha256, privateKey, encoding = 'hex') {
privateKey = PrivateKey(privateKey)
assert(privateKey, 'privateKey required')

var der, e, ecsignature, i, lenR, lenS, nonce;
var der, e, ecsignature, i, lenR, lenS, nonce, ypar;
i = null;
nonce = 0;
e = BigInteger.fromBuffer(dataSha256);
while (true) {
ecsignature = ecdsa.sign(curve, dataSha256, privateKey.d, nonce++);
[ecsignature, ypar] = ecdsa.sign(curve, dataSha256, privateKey.d, nonce++);
der = ecsignature.toDER();
lenR = der[3];
lenS = der[5 + lenR];
if (lenR === 32 && lenS === 32) {
i = ecdsa.calcPubKeyRecoveryParam(curve, e, ecsignature, privateKey.toPublic().Q);
i = ypar;// ecdsa.calcPubKeyRecoveryParam
i += 4; // compressed
i += 27; // compact // 24 or 27 :( forcing odd-y 2nd key candidate)
break;
Expand Down