public static byte[] UnbundleKeyFetchResponse(string key, string bundleHex)
{
byte[] bundle = BinaryHelper.FromHexString(bundleHex); // bundle
byte[] bundleKey = BinaryHelper.FromHexString(key); // key
BundleKeys keys = DeriveBundleKeys(bundleKey, "account/keys");
byte[] cipherText = bundle.Take(64).ToArray();
byte[] expectedHmac = bundle.Skip(bundle.Length - 32).Take(32).ToArray();
using (var hmac = new HMACSHA256(keys.HmacKey))
{
if (!BinaryHelper.AreEqual(expectedHmac, hmac.ComputeHash(cipherText)))
{
throw new Exception("Bad HMac.");
}
}
byte[] keyAWrapB = BinaryHelper.Xor(bundle.Take(64).ToArray(), keys.XorKey);
byte[] kA = keyAWrapB.Take(32).ToArray();
byte[] wrapKB = keyAWrapB.Skip(32).ToArray();
return(wrapKB);
}