using System;

using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Modes;
using Org.BouncyCastle.Crypto.Paddings;
using Org.BouncyCastle.Crypto.Parameters;

namespace Org.BouncyCastle.Crypto.Macs
{
	/**
	* DES based CBC Block Cipher MAC according to ISO9797, algorithm 3 (ANSI X9.19 Retail MAC)
	*
	* This could as well be derived from CBCBlockCipherMac, but then the property mac in the base
	* class must be changed to protected
	*/
	public class ISO9797Alg3Mac : IMac
	{
		private byte[] mac;
		private byte[] buf;
		private int bufOff;
		private IBlockCipher cipher;
		private IBlockCipherPadding padding;
		private int macSize;
		private KeyParameter lastKey2;
		private KeyParameter lastKey3;

		/**
		* create a Retail-MAC based on a CBC block cipher. This will produce an
		* authentication code of the length of the block size of the cipher.
		*
		* @param cipher the cipher to be used as the basis of the MAC generation. This must
		* be DESEngine.
		*/
		public ISO9797Alg3Mac(
			IBlockCipher cipher)
			: this(cipher, cipher.GetBlockSize() * 8, null)
		{
		}

		/**
		* create a Retail-MAC based on a CBC block cipher. This will produce an
		* authentication code of the length of the block size of the cipher.
		*
		* @param cipher the cipher to be used as the basis of the MAC generation.
		* @param padding the padding to be used to complete the last block.
		*/
		public ISO9797Alg3Mac(
			IBlockCipher		cipher,
			IBlockCipherPadding	padding)
			: this(cipher, cipher.GetBlockSize() * 8, padding)
		{
		}

		/**
		* create a Retail-MAC based on a block cipher with the size of the
		* MAC been given in bits. This class uses single DES CBC mode as the basis for the
		* MAC generation.
		* <p>
		* Note: the size of the MAC must be at least 24 bits (FIPS Publication 81),
		* or 16 bits if being used as a data authenticator (FIPS Publication 113),
		* and in general should be less than the size of the block cipher as it reduces
		* the chance of an exhaustive attack (see Handbook of Applied Cryptography).
		* </p>
		* @param cipher the cipher to be used as the basis of the MAC generation.
		* @param macSizeInBits the size of the MAC in bits, must be a multiple of 8.
		*/
		public ISO9797Alg3Mac(
			IBlockCipher	cipher,
			int				macSizeInBits)
			: this(cipher, macSizeInBits, null)
		{
		}

		/**
		* create a standard MAC based on a block cipher with the size of the
		* MAC been given in bits. This class uses single DES CBC mode as the basis for the
		* MAC generation. The final block is decrypted and then encrypted using the
		* middle and right part of the key.
		* <p>
		* Note: the size of the MAC must be at least 24 bits (FIPS Publication 81),
		* or 16 bits if being used as a data authenticator (FIPS Publication 113),
		* and in general should be less than the size of the block cipher as it reduces
		* the chance of an exhaustive attack (see Handbook of Applied Cryptography).
		* </p>
		* @param cipher the cipher to be used as the basis of the MAC generation.
		* @param macSizeInBits the size of the MAC in bits, must be a multiple of 8.
		* @param padding the padding to be used to complete the last block.
		*/
		public ISO9797Alg3Mac(
			IBlockCipher		cipher,
			int					macSizeInBits,
			IBlockCipherPadding	padding)
		{
			if ((macSizeInBits % 8) != 0)
				throw new ArgumentException("MAC size must be multiple of 8");

			if (!(cipher is DesEngine))
				throw new ArgumentException("cipher must be instance of DesEngine");

			this.cipher = new CbcBlockCipher(cipher);
			this.padding = padding;
			this.macSize = macSizeInBits / 8;

			mac = new byte[cipher.GetBlockSize()];
			buf = new byte[cipher.GetBlockSize()];
			bufOff = 0;
		}

		public string AlgorithmName
		{
			get { return "ISO9797Alg3"; }
		}

		public void Init(
			ICipherParameters parameters)
		{
			Reset();

			if (!(parameters is KeyParameter))
				throw new ArgumentException("parameters must be an instance of KeyParameter");

			// KeyParameter must contain a double or triple length DES key,
			// however the underlying cipher is a single DES. The middle and
			// right key are used only in the final step.

			KeyParameter kp = (KeyParameter)parameters;
			KeyParameter key1;
			byte[] keyvalue = kp.GetKey();

			if (keyvalue.Length == 16)
			{ // Double length DES key
				key1 = new KeyParameter(keyvalue, 0, 8);
				this.lastKey2 = new KeyParameter(keyvalue, 8, 8);
				this.lastKey3 = key1;
			}
			else if (keyvalue.Length == 24)
			{ // Triple length DES key
				key1 = new KeyParameter(keyvalue, 0, 8);
				this.lastKey2 = new KeyParameter(keyvalue, 8, 8);
				this.lastKey3 = new KeyParameter(keyvalue, 16, 8);
			}
			else
			{
				throw new ArgumentException("Key must be either 112 or 168 bit long");
			}

			cipher.Init(true, key1);
		}

		public int GetMacSize()
		{
			return macSize;
		}

		public void Update(
			byte input)
		{
			if (bufOff == buf.Length)
			{
				cipher.ProcessBlock(buf, 0, mac, 0);
				bufOff = 0;
			}

			buf[bufOff++] = input;
		}

		public void BlockUpdate(
			byte[]	input,
			int		inOff,
			int		len)
		{
			if (len < 0)
				throw new ArgumentException("Can't have a negative input length!");

			int blockSize = cipher.GetBlockSize();
			int resultLen = 0;
			int gapLen = blockSize - bufOff;

			if (len > gapLen)
			{
				Array.Copy(input, inOff, buf, bufOff, gapLen);

				resultLen += cipher.ProcessBlock(buf, 0, mac, 0);

				bufOff = 0;
				len -= gapLen;
				inOff += gapLen;

				while (len > blockSize)
				{
					resultLen += cipher.ProcessBlock(input, inOff, mac, 0);

					len -= blockSize;
					inOff += blockSize;
				}
			}

			Array.Copy(input, inOff, buf, bufOff, len);

			bufOff += len;
		}

		public int DoFinal(
			byte[]	output,
			int		outOff)
		{
			int blockSize = cipher.GetBlockSize();

			if (padding == null)
			{
				// pad with zeroes
				while (bufOff < blockSize)
				{
					buf[bufOff++] = 0;
				}
			}
			else
			{
				if (bufOff == blockSize)
				{
					cipher.ProcessBlock(buf, 0, mac, 0);
					bufOff = 0;
				}

				padding.AddPadding(buf, bufOff);
			}

			cipher.ProcessBlock(buf, 0, mac, 0);

			// Added to code from base class
			DesEngine deseng = new DesEngine();

			deseng.Init(false, this.lastKey2);
			deseng.ProcessBlock(mac, 0, mac, 0);

			deseng.Init(true, this.lastKey3);
			deseng.ProcessBlock(mac, 0, mac, 0);
			// ****

			Array.Copy(mac, 0, output, outOff, macSize);

			Reset();

			return macSize;
		}

		/**
		* Reset the mac generator.
		*/
		public void Reset()
		{
			Array.Clear(buf, 0, buf.Length);
			bufOff = 0;

			// reset the underlying cipher.
			cipher.Reset();
		}
	}
}
