77 lines
2.3 KiB
TypeScript
77 lines
2.3 KiB
TypeScript
function powMod(x: bigint, power: number, modulo: bigint): bigint {
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for (let i = 0; i < power; i++) {
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x = (x * x) % modulo;
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}
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return x;
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}
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function sqrtMod(x: bigint, P: bigint): bigint {
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const b2 = (x * x * x) % P;
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const b3 = (b2 * b2 * x) % P;
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const b6 = (powMod(b3, 3, P) * b3) % P;
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const b9 = (powMod(b6, 3, P) * b3) % P;
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const b11 = (powMod(b9, 2, P) * b2) % P;
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const b22 = (powMod(b11, 11, P) * b11) % P;
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const b44 = (powMod(b22, 22, P) * b22) % P;
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const b88 = (powMod(b44, 44, P) * b44) % P;
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const b176 = (powMod(b88, 88, P) * b88) % P;
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const b220 = (powMod(b176, 44, P) * b44) % P;
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const b223 = (powMod(b220, 3, P) * b3) % P;
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const t1 = (powMod(b223, 23, P) * b22) % P;
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const t2 = (powMod(t1, 6, P) * b2) % P;
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const root = powMod(t2, 2, P);
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return root;
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}
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const curveP = BigInt(`0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F`);
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/**
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* This function tells whether the point given is a DER encoded point on the ECDSA curve.
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* @param {string} pointHex The point as a hex string (*must not* include a '0x' prefix)
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* @returns {boolean} true if the point is on the SECP256K1 curve
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*/
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export function isPoint(pointHex: string): boolean {
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if (!pointHex?.length) {
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return false;
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}
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if (
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!(
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// is uncompressed
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(
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(pointHex.length === 130 && pointHex.startsWith('04')) ||
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// OR is compressed
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(pointHex.length === 66 &&
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(pointHex.startsWith('02') || pointHex.startsWith('03')))
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)
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)
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) {
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return false;
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}
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// Function modified slightly from noble-curves
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// Now we know that pointHex is a 33 or 65 byte hex string.
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const isCompressed = pointHex.length === 66;
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const x = BigInt(`0x${pointHex.slice(2, 66)}`);
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if (x >= curveP) {
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return false;
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}
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if (!isCompressed) {
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const y = BigInt(`0x${pointHex.slice(66, 130)}`);
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if (y >= curveP) {
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return false;
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}
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// Just check y^2 = x^3 + 7 (secp256k1 curve)
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return (y * y) % curveP === (x * x * x + 7n) % curveP;
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} else {
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// Get unaltered y^2 (no mod p)
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const ySquared = (x * x * x + 7n) % curveP;
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// Try to sqrt it, it will round down if not perfect root
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const y = sqrtMod(ySquared, curveP);
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// If we square and it's equal, then it was a perfect root and valid point.
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return (y * y) % curveP === ySquared;
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}
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} |