// Copyright (c) 2010 Gareth Lennox (garethl@dwakn.com)
// All rights reserved.

// Redistribution and use in source and binary forms, with or without modification,
// are permitted provided that the following conditions are met:

//     * Redistributions of source code must retain the above copyright notice,
//       this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright notice,
//       this list of conditions and the following disclaimer in the documentation
//       and/or other materials provided with the distribution.
//     * Neither the name of Gareth Lennox nor the names of its
//       contributors may be used to endorse or promote products derived from this
//       software without specific prior written permission.

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
// THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

using System;
using System.Security.Cryptography;

namespace libhac.XTSSharp
{
    /// <summary>
    /// Xts. See <see cref="XtsAes128"/> and <see cref="XtsAes256"/>.
    /// </summary>
    public class Xts
    {
        private readonly SymmetricAlgorithm _key1;
        private readonly SymmetricAlgorithm _key2;

        /// <summary>
        /// Creates a new Xts implementation.
        /// </summary>
        /// <param name="create">Function to create the implementations</param>
        /// <param name="key1">Key 1</param>
        /// <param name="key2">Key 2</param>
        protected Xts(Func<SymmetricAlgorithm> create, byte[] key1, byte[] key2)
        {
            if (create == null)
                throw new ArgumentNullException("create");
            if (key1 == null)
                throw new ArgumentNullException("key1");
            if (key2 == null)
                throw new ArgumentNullException("key2");

            _key1 = create();
            _key2 = create();

            if (key1.Length != key2.Length)
                throw new ArgumentException("Key lengths don't match");

            //set the key sizes
            _key1.KeySize = key1.Length * 8;
            _key2.KeySize = key2.Length * 8;

            //set the keys
            _key1.Key = key1;
            _key2.Key = key2;

            //ecb mode
            _key1.Mode = CipherMode.ECB;
            _key2.Mode = CipherMode.ECB;

            //no padding - we're always going to be writing full blocks
            _key1.Padding = PaddingMode.None;
            _key2.Padding = PaddingMode.None;

            //fixed block size of 128 bits.
            _key1.BlockSize = 16 * 8;
            _key2.BlockSize = 16 * 8;
        }

        /// <summary>
        /// Creates an xts encryptor
        /// </summary>
        public XtsCryptoTransform CreateEncryptor()
        {
            return new XtsCryptoTransform(_key1.CreateEncryptor(), _key2.CreateEncryptor(), false);
        }

        /// <summary>
        /// Creates an xts decryptor
        /// </summary>
        public XtsCryptoTransform CreateDecryptor()
        {
            return new XtsCryptoTransform(_key1.CreateDecryptor(), _key2.CreateEncryptor(), true);
        }

        /// <summary>
        /// Verify that the key is of an expected size of bits
        /// </summary>
        /// <param name="expectedSize">Expected size of the key in bits</param>
        /// <param name="key">The key</param>
        /// <returns>The key</returns>
        /// <exception cref="ArgumentNullException">If the key is null</exception>
        /// <exception cref="ArgumentException">If the key length does not match the expected length</exception>
        protected static byte[] VerifyKey(int expectedSize, byte[] key)
        {
            if (key == null)
                throw new ArgumentNullException("key");

            if (key.Length * 8 != expectedSize)
                throw new ArgumentException(string.Format("Expected key length of {0} bits, got {1}", expectedSize, key.Length * 8));

            return key;
        }
    }
}