/// <summary>
/// Creates a new session paket crypto service.
/// </summary>
/// <param name="sessionKey"></param>
/// <param name="isForEncryption"></param>
/// <param name="hmacKey"></param>
public SessionARC4NPacketCryptoService([NotNull] byte[] sessionKey, bool isForEncryption, [NotNull] byte[] hmacKey)
{
if (sessionKey == null)
{
throw new ArgumentNullException(nameof(sessionKey));
}
if (hmacKey == null)
{
throw new ArgumentNullException(nameof(hmacKey));
}
//RC4-Drop[n] for security
//Build an RC4 cipher service for the provided session key.
using (HMACSHA1 hmacsha = new HMACSHA1(hmacKey))
rc4CryptoService = new RC4DropNCryptoServiceProvider(hmacsha.ComputeHash(sessionKey), 1024, isForEncryption);
}
/// <summary>
/// Creates a new RC4 service with the provided <see cref="key"/> and follows
/// RC4-Drop[n].
/// </summary>
/// <param name="key">The RC4 key.</param>
/// <param name="n">The n value to be used in RC4-Drop[n]</param>
public RC4DropNCryptoServiceProvider([NotNull] byte[] key, int n, bool forEncryption)
{
if (key == null)
{
throw new ArgumentNullException(nameof(key));
}
internalRC4Engine = new RC4CryptoServiceProvider(key, forEncryption);
//TODO: Create a shared n buffer to be used. Only matters for server. Client only makes one usually.
byte[] dropNByteArray = new byte[n];
//Once initialized we need to drop the first n bytes.
//This prevents a common RC4 exploit that can determine key values otherwise.
internalRC4Engine.ProcessBytes(dropNByteArray, 0, n, dropNByteArray, 0);
}
