C# Steam WebRequests

i am beginner. I encountered a problem when trying to login to Steam.

 public Steam(string password, string login)
{
    Password = password;
    Login = login;
    _client.DefaultRequestHeaders.Add("User-Agent",
        "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36");
    _rsa = new RSACryptoServiceProvider();
    _rsaParameters = new RSAParameters();
    _params = new Dictionary<string, string>();

}
 public async Task GetRsa()
    {
        var request = await _client.GetAsync($"http://ift.tt/2oSwFes" + Login);
        var content = await request.Content.ReadAsStringAsync();                
        Timestamp = content.Between("timestamp\":\"", "\"", StringComparison.InvariantCulture);
        TokenGid = content.Between("token_gid\":\"", "\"", StringComparison.InvariantCulture);
        Mod = content.Between("publickey_mod\":\"", "\"", StringComparison.InvariantCulture);
        Exp = content.Between("publickey_exp\":\"", "\"", StringComparison.InvariantCulture);
        _rsaParameters.Modulus = HexToByte(Mod);
        _rsaParameters.Exponent = HexToByte(Exp);
        _rsa.ImportParameters(_rsaParameters);
        var bytePassword = Encoding.ASCII.GetBytes(Password);
        var encodedPassword = _rsa.Encrypt(bytePassword, false);
        EncryptedBase64Password = Convert.ToBase64String(encodedPassword);
    }
    public async Task TryLogin()
    {
        var unixTimestamp = (int)(DateTime.UtcNow.Subtract(new DateTime(1970, 1, 1))).TotalSeconds;
        //_params["donotcache"] = unixTimestamp + "000";
        _params["username"] = Login;
        _params["password"] = EncryptedBase64Password;
        _params["twofactorcode"] = "";
        _params["emailauth"] = "";
        _params["loginfriendlyname"] = "";
        _params["captchagid"] = "-1";
        _params["captcha_text"] = "";
        _params["emailsteamid"] = "";
        _params["rsatimestamp"] = Timestamp;
        _params["remember_login"] = "false";

        var responce2 =
            await _client.PostAsync($"http://ift.tt/2oyAKBp", new FormUrlEncodedContent(_params));
        var content2 = await responce2.Content.ReadAsStringAsync();
    }

In answer i have this:

"success":false,"requires_twofactor":false,"message":"The account name or password that you have entered is incorrect.","clear_password_field":true,"captcha_needed":false,"captcha_gid":-1

And i don't understand where is my mistakes. May be my RSA crypt is wrong or some trouble with coockies.