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
 *
 * @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 } from "../../types/bit_vec/module.f.js";
import { empty, msb, vec, vec8 } from "../../types/bit_vec/module.f.js";
import { flip } from "../../types/function/module.f.js";
import { repeat } from "../../types/monoid/module.f.js";
import { computeSync } from "../sha2/module.f.js";
const { concat } = msb;
/**
 * Outer padding.
 */
const oPad = vec8(0x5cn);
/**
 * Inner padding.
 */
const iPad = vec8(0x36n);
/**
 * Repeats a vector to create a padded block of the desired length.
 */
const padRepeat = repeat({ identity: empty, operation: concat });
/**
 * Generates an HMAC (Hash-based Message Authentication Code) using the specified SHA-2 hash function.
 *
 * @param sha2 - The SHA-2 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 = (sha2) => {
    const { blockLength } = sha2;
    const p = flip(padRepeat)(blockLength >> 3n);
    const ip = p(iPad);
    const op = p(oPad);
    const c = computeSync(sha2);
    const vbl = vec(blockLength);
    const xor = (a) => (b) => vbl(a ^ b);
    return k => m => {
        const k1 = length(k) > blockLength ? c([k]) : k;
        const k2 = concat(k1)(vec(blockLength - length(k1))(0n));
        const xk2 = xor(k2);
        const f = (p, msg) => c([xk2(p), msg]);
        const m1 = f(ip, m);
        return f(op, m1);
    };
};