staticrypt/lib/cryptoEngine.js

Password protect a static HTML file without a backend - StatiCrypt uses AES-256 wiht WebCrypto to encrypt your input with your long password and put it in a HTML file with a password prompt that can decrypted in-browser (client side).

const crypto = typeof window === "undefined" ? require("node:crypto").webcrypto : window.crypto;
const { subtle } = crypto;

const IV_BITS = 16 * 8;
const HEX_BITS = 4;
const ENCRYPTION_ALGO = "AES-CBC";

/**
 * Translates between utf8 encoded hexadecimal strings
 * and Uint8Array bytes.
 */
const HexEncoder = {
    /**
     * hex string -> bytes
     * @param {string} hexString
     * @returns {Uint8Array}
     */
    parse: function (hexString) {
        if (hexString.length % 2 !== 0) throw "Invalid hexString";
        const arrayBuffer = new Uint8Array(hexString.length / 2);

        for (let i = 0; i < hexString.length; i += 2) {
            const byteValue = parseInt(hexString.substring(i, i + 2), 16);
            if (isNaN(byteValue)) {
                throw "Invalid hexString";
            }
            arrayBuffer[i / 2] = byteValue;
        }
        return arrayBuffer;
    },

    /**
     * bytes -> hex string
     * @param {Uint8Array} bytes
     * @returns {string}
     */
    stringify: function (bytes) {
        const hexBytes = [];

        for (let i = 0; i < bytes.length; ++i) {
            let byteString = bytes[i].toString(16);
            if (byteString.length < 2) {
                byteString = "0" + byteString;
            }
            hexBytes.push(byteString);
        }
        return hexBytes.join("");
    },
};

/**
 * Translates between utf8 strings and Uint8Array bytes.
 */
const UTF8Encoder = {
    parse: function (str) {
        return new TextEncoder().encode(str);
    },

    stringify: function (bytes) {
        return new TextDecoder().decode(bytes);
    },
};

/**
 * Salt and encrypt a msg with a password.
 */
async function encrypt(msg, hashedPassword) {
    // Must be 16 bytes, unpredictable, and preferably cryptographically random. However, it need not be secret.
    // https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/encrypt#parameters
    const iv = crypto.getRandomValues(new Uint8Array(IV_BITS / 8));

    const key = await subtle.importKey("raw", HexEncoder.parse(hashedPassword), ENCRYPTION_ALGO, false, ["encrypt"]);

    const encrypted = await subtle.encrypt(
        {
            name: ENCRYPTION_ALGO,
            iv: iv,
        },
        key,
        UTF8Encoder.parse(msg)
    );

    // iv will be 32 hex characters, we prepend it to the ciphertext for use in decryption
    return HexEncoder.stringify(iv) + HexEncoder.stringify(new Uint8Array(encrypted));
}
exports.encrypt = encrypt;

/**
 * Decrypt a salted msg using a password.
 *
 * @param {string} encryptedMsg
 * @param {string} hashedPassword
 * @returns {Promise<string>}
 */
async function decrypt(encryptedMsg, hashedPassword) {
    const ivLength = IV_BITS / HEX_BITS;
    const iv = HexEncoder.parse(encryptedMsg.substring(0, ivLength));
    const encrypted = encryptedMsg.substring(ivLength);

    const key = await subtle.importKey("raw", HexEncoder.parse(hashedPassword), ENCRYPTION_ALGO, false, ["decrypt"]);

    const outBuffer = await subtle.decrypt(
        {
            name: ENCRYPTION_ALGO,
            iv: iv,
        },
        key,
        HexEncoder.parse(encrypted)
    );

    return UTF8Encoder.stringify(new Uint8Array(outBuffer));
}
exports.decrypt = decrypt;

/**
 * Salt and hash the password so it can be stored in localStorage without opening a password reuse vulnerability.
 *
 * @param {string} password
 * @param {string} salt
 * @returns {Promise<string>}
 */
async function hashPassword(password, salt) {
    // we hash the password in multiple steps, each adding more iterations. This is because we used to allow less
    // iterations, so for backward compatibility reasons, we need to support going from that to more iterations.
    let hashedPassword = await hashLegacyRound(password, salt);

    hashedPassword = await hashSecondRound(hashedPassword, salt);

    return hashThirdRound(hashedPassword, salt);
}
exports.hashPassword = hashPassword;

/**
 * This hashes the password with 1k iterations. This is a low number, we need this function to support backwards
 * compatibility.
 *
 * @param {string} password
 * @param {string} salt
 * @returns {Promise<string>}
 */
function hashLegacyRound(password, salt) {
    return pbkdf2(password, salt, 1000, "SHA-1");
}
exports.hashLegacyRound = hashLegacyRound;

/**
 * Add a second round of iterations. This is because we used to use 1k, so for backwards compatibility with
 * remember-me/autodecrypt links, we need to support going from that to more iterations.
 *
 * @param hashedPassword
 * @param salt
 * @returns {Promise<string>}
 */
function hashSecondRound(hashedPassword, salt) {
    return pbkdf2(hashedPassword, salt, 14000, "SHA-256");
}
exports.hashSecondRound = hashSecondRound;

/**
 * Add a third round of iterations to bring total number to 600k. This is because we used to use 1k, then 15k, so for
 * backwards compatibility with remember-me/autodecrypt links, we need to support going from that to more iterations.
 *
 * @param hashedPassword
 * @param salt
 * @returns {Promise<string>}
 */
function hashThirdRound(hashedPassword, salt) {
    return pbkdf2(hashedPassword, salt, 585000, "SHA-256");
}
exports.hashThirdRound = hashThirdRound;

/**
 * Salt and hash the password so it can be stored in localStorage without opening a password reuse vulnerability.
 *
 * @param {string} password
 * @param {string} salt
 * @param {int} iterations
 * @param {string} hashAlgorithm
 * @returns {Promise<string>}
 */
async function pbkdf2(password, salt, iterations, hashAlgorithm) {
    const key = await subtle.importKey("raw", UTF8Encoder.parse(password), "PBKDF2", false, ["deriveBits"]);

    const keyBytes = await subtle.deriveBits(
        {
            name: "PBKDF2",
            hash: hashAlgorithm,
            iterations,
            salt: UTF8Encoder.parse(salt),
        },
        key,
        256
    );

    return HexEncoder.stringify(new Uint8Array(keyBytes));
}

function generateRandomSalt() {
    const bytes = crypto.getRandomValues(new Uint8Array(128 / 8));

    return HexEncoder.stringify(new Uint8Array(bytes));
}
exports.generateRandomSalt = generateRandomSalt;

async function signMessage(hashedPassword, message) {
    const key = await subtle.importKey(
        "raw",
        HexEncoder.parse(hashedPassword),
        {
            name: "HMAC",
            hash: "SHA-256",
        },
        false,
        ["sign"]
    );
    const signature = await subtle.sign("HMAC", key, UTF8Encoder.parse(message));

    return HexEncoder.stringify(new Uint8Array(signature));
}
exports.signMessage = signMessage;

function getRandomAlphanum() {
    const possibleCharacters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

    let byteArray;
    let parsedInt;

    // Keep generating new random bytes until we get a value that falls
    // within a range that can be evenly divided by possibleCharacters.length
    do {
        byteArray = crypto.getRandomValues(new Uint8Array(1));
        // extract the lowest byte to get an int from 0 to 255 (probably unnecessary, since we're only generating 1 byte)
        parsedInt = byteArray[0] & 0xff;
    } while (parsedInt >= 256 - (256 % possibleCharacters.length));

    // Take the modulo of the parsed integer to get a random number between 0 and totalLength - 1
    const randomIndex = parsedInt % possibleCharacters.length;

    return possibleCharacters[randomIndex];
}

/**
 * Generate a random string of a given length.
 *
 * @param {int} length
 * @returns {string}
 */
function generateRandomString(length) {
    let randomString = "";

    for (let i = 0; i < length; i++) {
        randomString += getRandomAlphanum();
    }

    return randomString;
}
exports.generateRandomString = generateRandomString;