//
// MACAlgorithm.cs: Handles MAC with any symmetric algorithm
//
// Author:
//	Sebastien Pouliot (spouliot@motus.com)
//
// (C) 2002, 2003 Motus Technologies Inc. (http://www.motus.com)
// Copyright (C) 2004 Novell, Inc (http://www.novell.com)
//
// 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.
//

using System;
using System.Security.Cryptography;

namespace Mono.Security.Cryptography {

	// References:
	// a.	FIPS PUB 81: DES MODES OF OPERATION 
	//	MAC: Appendix F (MACDES not MACTripleDES but close enough ;-)
	//	http://www.itl.nist.gov/fipspubs/fip81.htm
	
	// Generic MAC mechanims - most of the work is done in here
	// It should work with any symmetric algorithm function e.g. DES for MACDES (fips81)
	internal class MACAlgorithm {

		private SymmetricAlgorithm algo;
		private ICryptoTransform enc;
		private byte[] block;
		private int blockSize;
		private int blockCount;

		public MACAlgorithm (SymmetricAlgorithm algorithm) 
		{
			algo = (SymmetricAlgorithm) algorithm;
			algo.Mode = CipherMode.CBC;
			blockSize = (algo.BlockSize >> 3); // in bytes
			algo.IV = new byte [blockSize];
			block = new byte [blockSize];
		}
	
		public void Initialize (byte[] key) 
		{
			algo.Key = key;
			// note: the encryptor transform may be reusable - see Final
			if (enc == null) {
				enc = algo.CreateEncryptor ();
			}
			Array.Clear (block, 0, blockSize);
			blockCount = 0;
		}
		
		public void Core (byte[] rgb, int ib, int cb) 
		{
			// 1. fill the rest of the "block"
			int n = System.Math.Min (blockSize - blockCount, cb);
			Array.Copy (rgb, ib, block, blockCount, n); 
			blockCount += n;
	
			// 2. if block is full then transform it
			if (blockCount == blockSize) {
				enc.TransformBlock (block, 0, blockSize, block, 0);
	
				// 3. transform any other full block in specified buffer
				int b = (int) ((cb - n) / blockSize);
				for (int i=0; i < b; i++) {
					enc.TransformBlock (rgb, n, blockSize, block, 0);
					n += blockSize;
				}
	
				// 4. if data is still present fill the "block" with the remainder
				blockCount = cb - n;
				if (blockCount > 0)
					Array.Copy (rgb, n, block, 0, blockCount);
			}
		}
	
		public byte[] Final () 
		{
			byte[] result;
			if ((blockCount > 0) || ((algo.Padding != PaddingMode.Zeros) && (algo.Padding != PaddingMode.None))) {
				result = enc.TransformFinalBlock (block, 0, blockCount);
			} else {
#if NET_1_0
				// add an empty (zeros) block for MAC padding
				byte[] emptyBlock = new byte [blockSize];
				result = enc.TransformFinalBlock (emptyBlock, 0, blockSize);
#else
				result = (byte[]) block.Clone ();
#endif
			}

			if (!enc.CanReuseTransform) {
				enc.Dispose ();
				enc = null;
			}
			return result;
		}
	}
}