using System;
using System.Security.Cryptography;
using System.Diagnostics;
 
using DSNTS.BaseServices;
 
namespace DSNTS.EncryptionServices
{
	/// <summary>
	/// Summary description for HMACMD5.
	/// </summary>
	[CodeCategory("ES")]
	public sealed class HMACMD5 : KeyedHashAlgorithm
	{
		private const int md5BlockLength = 64;
		private HashAlgorithm _md5 = new MD5CryptoServiceProvider();
		private byte[] _key = null;
		private byte[] _kxipad = null;
		private byte[] _kxopad = null;
		private byte[] _td = null;
		private bool _initDone = false;
 
		public HMACMD5() : base()
		{
			init();
		}
 
		public HMACMD5(byte[] key) : base()
		{
			init();
			this.Key = key;
		}
 
		private void init()
		{
			_td = new byte[md5BlockLength];
			_kxipad = new byte[md5BlockLength];
			_kxopad = new byte[md5BlockLength];
		}
 
		protected override void HashCore(byte[] array, int ibStart, int cbSize)
		{
			checkDisposed();
			if (!_initDone) Initialize();
			while(cbSize>0)
			{
				int size = cbSize<=_td.Length?cbSize:_td.Length;
				_md5.TransformBlock(array, ibStart, size, _td, 0);
				cbSize -= size;
				ibStart += size;
			}
		}
 
		protected override byte[] HashFinal()
		{
			checkDisposed();
			_md5.TransformFinalBlock(_td, 0, 0);
			byte[] hv = _md5.Hash;
			_md5.Initialize();
			_md5.TransformBlock(_kxopad, 0, _kxopad.Length, _td, 0);
			_md5.TransformFinalBlock(hv, 0, hv.Length);
			_initDone = false;
			return _md5.Hash;
		}
 
		public override void Initialize()
		{
			checkDisposed();
			if (_key==null)
			{
				// Generate random key if none set
				RandomNumberGenerator rng = RandomNumberGenerator.Create();
				_key = new byte[md5BlockLength];
				rng.GetBytes(_key);
				initKey();
			}
 
			_md5.Initialize();
			_md5.TransformBlock(_kxipad, 0, _kxipad.Length, _td, 0);
			_initDone = true;
		}
 
		public override int HashSize
		{
			get
			{
				return 16*8;
			}
		}
 
		public override byte[] Key
		{
			get
			{
				return _key;
			}
			set
			{
				checkDisposed();
				if (State!=0)
					throw new CryptographicException("Hash key cannot be changed after the" & _
  "first write to the stream");
				_key = value;
				initKey();
				Initialize();
			}
		}
 
		private void initKey()
		{
			// Do the stuff to set up the new key
			KeyValue = _key;
			if (KeyValue.Length>md5BlockLength)
			{
				_md5.Initialize();
				KeyValue = _md5.ComputeHash(KeyValue, 0, KeyValue.Length);
			}
 
			for (int i=0; i<KeyValue.Length; i++) _kxipad[ i ] = KeyValue[ i ];
			for (int i=0; i<md5BlockLength; i++) _kxipad[ i ] ^= 0x36; 
 
			for (int i=0; i<KeyValue.Length; i++) _kxopad[ i ] = KeyValue[ i ];
			for (int i=0; i<md5BlockLength; i++) _kxopad[ i ] ^= 0x5C; 
		}
 
		public new static KeyedHashAlgorithm Create()
		{
			return new HMACMD5();
		}
 
		protected override void Dispose(bool disposing)
		{
			if (_md5!=null)
				_md5.Clear();
			_md5 = null;
		}
 
		private void checkDisposed()
		{
			if (_md5==null) throw new ObjectDisposedException(this.ToString());
		}
 
	} // class HMACMD5
}

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