function importSecretKey(rawKey) {
  return crypto.subtle.importKey(
    "raw",
    rawKey,
    {length: 128, name: "AES-GCM"},
    true,
    ["encrypt", "decrypt"]
  );
}

function StrToBuffer(AInput) {
    return new Uint8Array(AInput.match(/[\da-f]{2}/gi).map(function (h) { return parseInt(h, 16) } ) )
}

function decryptMessage(aKey, aCipherText, aIV, aAAD, aTagLength = 96) {

  return crypto.subtle.decrypt(
    {
        name: "AES-GCM",
        iv: aIV,
        additionalData: aAAD,
        tagLength: aTagLength
    },
    aKey,
    aCipherText,
    )
}

function encryptMessage(aKey, aClearText, aIV, aAAD, aTagLength = 96) {

  return crypto.subtle.encrypt({
        name: 'AES-GCM',
        iv: aIV,
        additionalData: aAAD,
        tagLength: aTagLength
    }, aKey, aClearText);

}


var key = await importSecretKey(StrToBuffer('11111111111111111111111111111111'))
var iv = StrToBuffer('4D4554000000000100000000')
var aad = StrToBuffer('3033333333333333333333333333333333')

var ciphertext = StrToBuffer('b662a493a5dfdbccc1dc832271bae416945f2e0474d102d2c7941fcd50c678534083e5d1520ae04c3038a281d176b6b2a1ce6e15fe861f4689b7fe7909f309908a40f843e9ceff7675f00b0e217b7620')
var cleartext = StrToBuffer('0fc00000010c07e6091a0103272e5aff8880020209060001190900ff01010206090c07e6091a0103230000ff8880115a1749cb251d1749cb251d1749cb251d1749cb251d')

// encrypt to a 128 bit tag

var encMsg = await encryptMessage(key, cleartext, iv, aad, 128);

// decrypt and verify
var decMsg = await decryptMessage(key, encMsg, iv, aad, 128);

// decrypt original and verify
var decMsg = await decryptMessage(key, ciphertext, iv, aad, 96);

// decrypt truncated and verify
var decMsg = await decryptMessage(key, encMsg.slice(0, -4), iv, aad, 96)