using System;

using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Crypto.Utilities;

namespace Org.BouncyCastle.Crypto.Engines
{
	/**
	* HC-128 is a software-efficient stream cipher created by Hongjun Wu. It
	* generates keystream from a 128-bit secret key and a 128-bit initialization
	* vector.
	* <p>
	* http://www.ecrypt.eu.org/stream/p3ciphers/hc/hc128_p3.pdf
	* </p><p>
	* It is a third phase candidate in the eStream contest, and is patent-free.
	* No attacks are known as of today (April 2007). See
	*
	* http://www.ecrypt.eu.org/stream/hcp3.html
	* </p>
	*/
	public class HC128Engine
		: IStreamCipher
	{
		private uint[] p = new uint[512];
		private uint[] q = new uint[512];
		private uint cnt = 0;

		private static uint F1(uint x)
		{
			return RotateRight(x, 7) ^ RotateRight(x, 18) ^ (x >> 3);
		}

		private static uint F2(uint x)
		{
			return RotateRight(x, 17) ^ RotateRight(x, 19) ^ (x >> 10);
		}

		private uint G1(uint x, uint y, uint z)
		{
			return (RotateRight(x, 10) ^ RotateRight(z, 23)) + RotateRight(y, 8);
		}

		private uint G2(uint x, uint y, uint z)
		{
			return (RotateLeft(x, 10) ^ RotateLeft(z, 23)) + RotateLeft(y, 8);
		}

		private static uint RotateLeft(uint	x, int bits)
		{
			return (x << bits) | (x >> -bits);
		}

		private static uint RotateRight(uint x, int bits)
		{
			return (x >> bits) | (x << -bits);
		}

		private uint H1(uint x)
		{
			return q[x & 0xFF] + q[((x >> 16) & 0xFF) + 256];
		}

		private uint H2(uint x)
		{
			return p[x & 0xFF] + p[((x >> 16) & 0xFF) + 256];
		}

		private static uint Mod1024(uint x)
		{
			return x & 0x3FF;
		}

		private static uint Mod512(uint x)
		{
			return x & 0x1FF;
		}

		private static uint Dim(uint x, uint y)
		{
			return Mod512(x - y);
		}

		private uint Step()
		{
			uint j = Mod512(cnt);
			uint ret;
			if (cnt < 512)
			{
				p[j] += G1(p[Dim(j, 3)], p[Dim(j, 10)], p[Dim(j, 511)]);
				ret = H1(p[Dim(j, 12)]) ^ p[j];
			}
			else
			{
				q[j] += G2(q[Dim(j, 3)], q[Dim(j, 10)], q[Dim(j, 511)]);
				ret = H2(q[Dim(j, 12)]) ^ q[j];
			}
			cnt = Mod1024(cnt + 1);
			return ret;
		}

		private byte[] key, iv;
		private bool initialised;

		private void Init()
		{
			if (key.Length != 16)
				throw new ArgumentException("The key must be 128 bits long");

			cnt = 0;

			uint[] w = new uint[1280];

			for (int i = 0; i < 16; i++)
			{
				w[i >> 2] |= ((uint)key[i] << (8 * (i & 0x3)));
			}
			Array.Copy(w, 0, w, 4, 4);

			for (int i = 0; i < iv.Length && i < 16; i++)
			{
				w[(i >> 2) + 8] |= ((uint)iv[i] << (8 * (i & 0x3)));
			}
			Array.Copy(w, 8, w, 12, 4);

			for (uint i = 16; i < 1280; i++)
			{
				w[i] = F2(w[i - 2]) + w[i - 7] + F1(w[i - 15]) + w[i - 16] + i;
			}

			Array.Copy(w, 256, p, 0, 512);
			Array.Copy(w, 768, q, 0, 512);

			for (int i = 0; i < 512; i++)
			{
				p[i] = Step();
			}
			for (int i = 0; i < 512; i++)
			{
				q[i] = Step();
			}

			cnt = 0;
		}

		public string AlgorithmName
		{
			get { return "HC-128"; }
		}

		/**
		* Initialise a HC-128 cipher.
		*
		* @param forEncryption whether or not we are for encryption. Irrelevant, as
		*                      encryption and decryption are the same.
		* @param params        the parameters required to set up the cipher.
		* @throws ArgumentException if the params argument is
		*                                  inappropriate (ie. the key is not 128 bit long).
		*/
		public void Init(
			bool				forEncryption,
			ICipherParameters	parameters)
		{
			ICipherParameters keyParam = parameters;

			if (parameters is ParametersWithIV)
			{
				iv = ((ParametersWithIV)parameters).GetIV();
				keyParam = ((ParametersWithIV)parameters).Parameters;
			}
			else
			{
				iv = new byte[0];
			}

			if (keyParam is KeyParameter)
			{
				key = ((KeyParameter)keyParam).GetKey();
				Init();
			}
			else
			{
				throw new ArgumentException(
					"Invalid parameter passed to HC128 init - " + parameters.GetType().Name,
					"parameters");
			}

			initialised = true;
		}

		private byte[] buf = new byte[4];
		private int idx = 0;

		private byte GetByte()
		{
			if (idx == 0)
			{
				Pack.UInt32_To_LE(Step(), buf);				
			}
			byte ret = buf[idx];
			idx = idx + 1 & 0x3;
			return ret;
		}

		public void ProcessBytes(
			byte[]	input,
			int		inOff,
			int		len,
			byte[]	output,
			int		outOff)
		{
			if (!initialised)
				throw new InvalidOperationException(AlgorithmName + " not initialised");
			if ((inOff + len) > input.Length)
				throw new DataLengthException("input buffer too short");
			if ((outOff + len) > output.Length)
				throw new DataLengthException("output buffer too short");

			for (int i = 0; i < len; i++)
			{
				output[outOff + i] = (byte)(input[inOff + i] ^ GetByte());
			}
		}

		public void Reset()
		{
			idx = 0;
			Init();
		}

		public byte ReturnByte(byte input)
		{
			return (byte)(input ^ GetByte());
		}
	}
}
