/// <summary>
/// Update the decryption keys
/// </summary>
/// <param name="ch">Character to update the keys with</param>
protected void UpdateKeys(byte ch)
{
keys[0] = Crc32.ComputeCrc32(keys[0], ch);
keys[1] = keys[1] + (byte)keys[0];
keys[1] = keys[1] * 134775813 + 1;
keys[2] = Crc32.ComputeCrc32(keys[2], (byte)(keys[1] >> 24));
}
/// <summary>
/// Generates new encryption keys based on given seed
/// </summary>
/// <param name="seed">The seed value to initialise keys with.</param>
/// <returns>A new key value.</returns>
static public byte[] GenerateKeys(byte[] seed)
{
if (seed == null)
{
throw new ArgumentNullException("seed");
}
if (seed.Length == 0)
{
throw new ArgumentException("Length is zero", "seed");
}
uint[] newKeys = new uint[] {
0x12345678,
0x23456789,
0x34567890
};
for (int i = 0; i < seed.Length; ++i)
{
newKeys[0] = Crc32.ComputeCrc32(newKeys[0], seed[i]);
newKeys[1] = newKeys[1] + (byte)newKeys[0];
newKeys[1] = newKeys[1] * 134775813 + 1;
newKeys[2] = Crc32.ComputeCrc32(newKeys[2], (byte)(newKeys[1] >> 24));
}
byte[] result = new byte[12];
result[0] = (byte)(newKeys[0] & 0xff);
result[1] = (byte)((newKeys[0] >> 8) & 0xff);
result[2] = (byte)((newKeys[0] >> 16) & 0xff);
result[3] = (byte)((newKeys[0] >> 24) & 0xff);
result[4] = (byte)(newKeys[1] & 0xff);
result[5] = (byte)((newKeys[1] >> 8) & 0xff);
result[6] = (byte)((newKeys[1] >> 16) & 0xff);
result[7] = (byte)((newKeys[1] >> 24) & 0xff);
result[8] = (byte)(newKeys[2] & 0xff);
result[9] = (byte)((newKeys[2] >> 8) & 0xff);
result[10] = (byte)((newKeys[2] >> 16) & 0xff);
result[11] = (byte)((newKeys[2] >> 24) & 0xff);
return(result);
}