functionalscript/crypto/hmac/module.f.js

FunctionalScript is a purely functional subset of JavaScript

/**
 * Provides an implementation of HMAC (Hash-based Message Authentication Code).
 *
 * https://en.wikipedia.org/wiki/HMAC
 * https://www.rfc-editor.org/rfc/rfc2104
 *
 * @module
 *
 * @example
 *
 * ```ts
 * import { vec } from '../../types/bit_vec/module.f.ts'
 * import { msbUtf8 } from '../../text/module.f.ts'
 * import { sha256 } from '../sha2/module.f.ts'
 *
 * const r = hmac(sha256)(msbUtf8('key'))(msbUtf8('The quick brown fox jumps over the lazy dog'))
 * if (r !== vec(256n)(0xf7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8n)) { throw r }
 * ```
 */
import { length, msb, vec, vec8, repeat } from "../../types/bit_vec/module.f.js";
import { computeSync } from "../sha2/module.f.js";
const { concat, xor } = msb;
/**
 * Outer padding.
 */
const oPad = vec8(0x5cn);
/**
 * Inner padding.
 */
const iPad = vec8(0x36n);
/**
 * Generates an HMAC (Hash-based Message Authentication Code) using the specified hash function.
 *
 * @param hashFunc - The hash function implementation to use.
 * @returns - A function that takes a key and returns another function
 * that takes a message and computes the HMAC.
 */
export const hmac = (hashFunc) => {
    const { blockLength } = hashFunc;
    const p = repeat(blockLength >> 3n);
    const ip = p(iPad);
    const op = p(oPad);
    const c = computeSync(hashFunc);
    return k => {
        const k1 = length(k) > blockLength ? c([k]) : k;
        const k2 = concat(k1)(vec(blockLength - length(k1))(0n));
        const xk2 = xor(k2);
        const f = (p) => {
            const x = xk2(p);
            return (msg) => c([x, msg]);
        };
        const fip = f(ip);
        const fop = f(op);
        return m => fop(fip(m));
    };
};