//

// Copyright (c) 2008-2011, Kenneth Bell

//

// Permission is hereby granted, free of charge, to any person obtaining a

// copy of this software and associated documentation files (the "Software"),

// to deal in the Software without restriction, including without limitation

// the rights to use, copy, modify, merge, publish, distribute, sublicense,

// and/or sell copies of the Software, and to permit persons to whom the

// Software is furnished to do so, subject to the following conditions:

//

// The above copyright notice and this permission notice shall be included in

// all copies or substantial portions of the Software.

//

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER

// DEALINGS IN THE SOFTWARE.

//



namespace DiscUtils.Iscsi

{

    using System;

    using System.Globalization;

    using System.Security.Cryptography;

    using System.Text;



    internal class ChapAuthenticator : Authenticator

    {

        private State _state;



        private string _name;

        private string _password;



        private int _algorithm;

        private byte _identifier;

        private byte[] _challenge;



        public ChapAuthenticator(string name, string password)

        {

            _name = name;

            _password = password;

            _state = State.SendAlgorithm;

        }



        private enum State

        {

            SendAlgorithm,

            ReceiveChallenge,

            SendResponse,

            Finished

        }



        public override string Identifier

        {

            get { return "CHAP"; }

        }



        public override bool GetParameters(TextBuffer textBuffer)

        {

            switch (_state)

            {

                case State.SendAlgorithm:

                    textBuffer.Add("CHAP_A", "5");

                    _state = State.ReceiveChallenge;

                    return false;

                case State.SendResponse:

                    textBuffer.Add("CHAP_N", _name);

                    textBuffer.Add("CHAP_R", CalcResponse());

                    _state = State.Finished;

                    return true;

                default:

                    throw new InvalidOperationException("Unknown authentication state: " + _state);

            }

        }



        public override void SetParameters(TextBuffer textBuffer)

        {

            switch (_state)

            {

                case State.ReceiveChallenge:

                    _algorithm = int.Parse(textBuffer["CHAP_A"], CultureInfo.InvariantCulture);

                    _identifier = byte.Parse(textBuffer["CHAP_I"], CultureInfo.InvariantCulture);

                    _challenge = ParseByteString(textBuffer["CHAP_C"]);

                    _state = State.SendResponse;



                    if (_algorithm != 0x5)

                    {

                        throw new LoginException("Unexpected CHAP authentication algorithm: " + _algorithm);

                    }



                    return;

                default:

                    throw new InvalidOperationException("Unknown authentication state: " + _state);

            }

        }



        private static byte[] ParseByteString(string p)

        {

            if (!p.StartsWith("0x", StringComparison.OrdinalIgnoreCase))

            {

                throw new InvalidProtocolException("Invalid value in CHAP exchange");

            }



            byte[] data = new byte[(p.Length - 2) / 2];

            for (int i = 0; i < data.Length; ++i)

            {

                data[i] = byte.Parse(p.Substring(2 + (i * 2), 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture);

            }



            return data;

        }



        private string CalcResponse()

        {

            MD5 md5 = MD5CryptoServiceProvider.Create();



            byte[] toHash = new byte[1 + _password.Length + _challenge.Length];

            toHash[0] = _identifier;

            Encoding.ASCII.GetBytes(_password, 0, _password.Length, toHash, 1);

            Array.Copy(_challenge, 0, toHash, _password.Length + 1, _challenge.Length);



            byte[] hash = md5.ComputeHash(toHash);



            StringBuilder result = new StringBuilder("0x");

            for (int i = 0; i < hash.Length; ++i)

            {

                result.Append(hash[i].ToString("x2", CultureInfo.InvariantCulture));

            }



            return result.ToString();

        }

    }

}