Example AES-GCM encode-decode with string key

crypto-aes-gcm.js

// Sources:
// https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/importKey
// https://github.com/mdn/dom-examples/blob/main/web-crypto/encrypt-decrypt/aes-gcm.js
// https://github.com/diafygi/webcrypto-examples#aes-gcm

let enc = new TextEncoder();
let dec = new TextDecoder();

(async function () {
    additionalData = window.crypto.getRandomValues(new Uint8Array(32))
    iv = window.crypto.getRandomValues(new Uint8Array(12));
    key = await window.crypto.subtle.importKey(
        "raw",
        enc.encode("barracuda radish amenity pregame"),
        "AES-GCM",
        true,
        ["encrypt", "decrypt"]
    )

    function encrypt(key, text) {
        return window.crypto.subtle.encrypt(
            {
                name: "AES-GCM",

                //Don't re-use initialization vectors!
                //Always generate a new iv every time your encrypt!
                //Recommended to use 12 bytes length
                iv: iv,

                //Additional authentication data (optional)
                additionalData: additionalData,

                //Tag length (optional)
                tagLength: 128, //can be 32, 64, 96, 104, 112, 120 or 128 (default)
            },
            key, //from generateKey or importKey above
            enc.encode(text) //ArrayBuffer of data you want to encrypt
        )
    }

    function decrypt(key, text) {
        return window.crypto.subtle.decrypt(
            {
                name: "AES-GCM",
                iv: iv, //The initialization vector you used to encrypt
                additionalData: additionalData, //The addtionalData you used to encrypt (if any)
                tagLength: 128, //The tagLength you used to encrypt (if any)
            },
            key, //from generateKey or importKey above
            text //ArrayBuffer of the data
        )
    }

    function arrayBufferToBase64(buffer) {
        var binary = '';
        var bytes = new Uint8Array(buffer);
        var len = bytes.byteLength;
        for (var i = 0; i < len; i++) {
            binary += String.fromCharCode(bytes[i]);
        }
        return window.btoa(binary);
    }

    function base64ToArrayBuffer(base64) {
        var binary_string = window.atob(base64);
        var len = binary_string.length;
        var bytes = new Uint8Array(len);
        for (var i = 0; i < len; i++) {
            bytes[i] = binary_string.charCodeAt(i);
        }
        return bytes.buffer;
    }

    let encryptedBuffer = await encrypt(key, "Message For Encode"); // ArrayBuffer Encrypted Message
    let encryptedText = arrayBufferToBase64(encryptedBuffer); // Base64 Encrypted Message

    let arrayBufferEncrypted = base64ToArrayBuffer(encryptedText); // ArrayBuffer Encrypted Message
    let decryptedBuffer = await decrypt(key, arrayBufferEncrypted); // ArrayBuffer Decrypted Message
    let decryptedText = dec.decode(decryptedBuffer);

    console.log('Encrypted: ' + encryptedText)
    console.log('Decrypted: ' + decryptedText)
})()