1ef4afc82d
Co-authored-by: GCHQDeveloper581 <63102987+GCHQDeveloper581@users.noreply.github.com> (initial tests)
74 lines
1.6 KiB
JavaScript
74 lines
1.6 KiB
JavaScript
/**
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* @author p-leriche [philip.leriche@cantab.net]
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* @copyright Crown Copyright 2025
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* @license Apache-2.0
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*/
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import OperationError from "../errors/OperationError.mjs";
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/**
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* Number theory utilities used by cryptographic operations.
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*
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* Currently provides:
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* - parseBigInt
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* - Extended Euclidean Algorithm
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* - Modular Exponentiation
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*
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* Additional algorithms may be added as required.
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*/
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/**
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* parseBigInt helper operation
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*/
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export function parseBigInt(value, param) {
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const v = (value ?? "").trim();
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if (/^0x[0-9a-f]+$/i.test(v)) return BigInt(v);
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if (/^[+-]?[0-9]+$/.test(v)) return BigInt(v);
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throw new OperationError(param + " must be decimal or hex (0x...)");
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}
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/**
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* Extended Euclidean Algorithm
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*
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* Returns [g, x, y] such that:
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* a*x + b*y = g = gcd(a, b)
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*
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* (Uses an iterative algorithm to avoid possible stack overflow)
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*/
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export function egcd(a, b) {
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let oldR = a, r = b;
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let oldS = 1n, s = 0n;
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let oldT = 0n, t = 1n;
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while (r !== 0n) {
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const quotient = oldR / r;
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[oldR, r] = [r, oldR - quotient * r];
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[oldS, s] = [s, oldS - quotient * s];
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[oldT, t] = [t, oldT - quotient * t];
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}
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// oldR is the gcd
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// oldS and oldT are the Bézout coefficients
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return [oldR, oldS, oldT];
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}
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/**
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* Modular exponentiation
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*/
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export function modPow(base, exponent, modulus) {
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let result = 1n;
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base %= modulus;
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while (exponent > 0n) {
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if (exponent & 1n) {
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result = (result * base) % modulus;
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}
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base = (base * base) % modulus;
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exponent >>= 1n;
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}
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return result;
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}
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