VRCX/html/src/security.js

const defaultAESKey = new TextEncoder().encode(
    'https://github.com/pypy-vrc/VRCX'
);

const hexToUint8Array = (hexStr) => {
    const r = hexStr.match(/.{1,2}/g);
    if (!r) return null;
    return new Uint8Array(r.map((b) => parseInt(b, 16)));
};

const uint8ArrayToHex = (arr) =>
    arr.reduce((str, byte) => str + byte.toString(16).padStart(2, '0'), '');

function stdAESKey(key) {
    const tKey = new TextEncoder().encode(key);
    let sk = tKey;
    if (key.length < 32) {
        sk = new Uint8Array(32);
        sk.set(tKey);
        sk.set(defaultAESKey.slice(key.length, 32), key.length);
    }
    return sk.slice(0, 32);
}

async function encrypt(plaintext, key) {
    let iv = window.crypto.getRandomValues(new Uint8Array(12));
    let sharedKey = await window.crypto.subtle.importKey(
        'raw',
        stdAESKey(key),
        {name: 'AES-GCM', length: 256},
        true,
        ['encrypt']
    );
    let cipher = await window.crypto.subtle.encrypt(
        {name: 'AES-GCM', iv},
        sharedKey,
        new TextEncoder().encode(plaintext)
    );
    let ciphertext = new Uint8Array(cipher);
    let encrypted = new Uint8Array(iv.length + ciphertext.byteLength);
    encrypted.set(iv, 0);
    encrypted.set(ciphertext, iv.length);
    return uint8ArrayToHex(encrypted);
}

async function decrypt(ciphertext, key) {
    let text = hexToUint8Array(ciphertext);
    if (!text) return '';
    let sharedKey = await window.crypto.subtle.importKey(
        'raw',
        stdAESKey(key),
        {name: 'AES-GCM', length: 256},
        true,
        ['decrypt']
    );
    let plaintext = await window.crypto.subtle.decrypt(
        {name: 'AES-GCM', iv: text.slice(0, 12)},
        sharedKey,
        text.slice(12)
    );
    return new TextDecoder().decode(new Uint8Array(plaintext));
}

export default {
    decrypt,
    encrypt
};