decode.cs

public void DecodeTEST(string uri, string bearer)
{
    var u = new System.Uri(uri, System.UriKind.RelativeOrAbsolute);
    var args = HttpUtility.ParseQueryString(u.Query).Get("args");

    Debug.Log("READ Query: args = " + args);

    using (var aes = new AesCryptoServiceProvider())
    {
        aes.Mode = CipherMode.CBC;
        aes.BlockSize = 128;
        aes.IV = new byte[] { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, };

        using (var md5 = MD5.Create())
        {
            aes.Key = md5.ComputeHash(Encoding.UTF8.GetBytes(bearer));
        }

        using (var ms = new System.IO.MemoryStream())
        {
            using (var cs = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Write))
            {
                var b = System.Convert.FromBase64String(args);
                cs.Write(b, 0, b.Length);
            }

            var decode = Encoding.UTF8.GetString(ms.GetBuffer());
            Debug.Log("DECODE Query: " + decode);

            var ds = HttpUtility.ParseQueryString(decode);
            for (int i = 0; i < ds.Count; i++)
            {
                Debug.Log(ds.GetKey(i) + ": " + ds.Get(i));
            }
        }
    }
}

test.cs

var url = "http://example.com:80/?args=QoSiR2w1QWf4fsgYsTuGocd6k%2BkQz55rN164cVJD2hZ3u3lBYrU4B9nQ3XB0%2F%2Bt%2FEGDXDiIb7UASdE8jYcePkJpnYzjb%2FFNmuWQgh0YrRTNXX%2FxciIcHVxpsOzxKmQ%2BrhLqBLp9iFbPgzG8ZRR8%2F%2BCmRyZmuU%2BqSP%2B8SEP%2FmAeg%3D";
var bearer = "DB270E0074BAD27C1177F31627818618";

DecodeTEST(url, bearer);

// DECODE Query: bearer=DB270E0074BAD27C1177F31627818618&time=4/18/2017 3:13:22 PM&salt=p70hmLGa/EDgmfmKxLwXqDORm1pZ/g2Y+ivtiwwurlk=
// bearer: DB270E0074BAD27C1177F31627818618
// time: 4/18/2017 3:13:22 PM
// salt: p70hmLGa/EDgmfmKxLwXqDORm1pZ/g2Y ivtiwwurlk=