init commit

output/Libraries/BouncyCastle.Crypto/Org/BouncyCastle/Crypto/Engines/XSalsa20Engine.cs

@@ -0,0 +1,36 @@
+using System;
+using Org.BouncyCastle.Crypto.Utilities;
+
+namespace Org.BouncyCastle.Crypto.Engines;
+
+public class XSalsa20Engine : Salsa20Engine
+{
+	public override string AlgorithmName => "XSalsa20";
+
+	protected override int NonceSize => 24;
+
+	protected override void SetKey(byte[] keyBytes, byte[] ivBytes)
+	{
+		if (keyBytes == null)
+		{
+			throw new ArgumentException(AlgorithmName + " doesn't support re-init with null key");
+		}
+		if (keyBytes.Length != 32)
+		{
+			throw new ArgumentException(AlgorithmName + " requires a 256 bit key");
+		}
+		base.SetKey(keyBytes, ivBytes);
+		Pack.LE_To_UInt32(ivBytes, 8, engineState, 8, 2);
+		uint[] array = new uint[engineState.Length];
+		Salsa20Engine.SalsaCore(20, engineState, array);
+		engineState[1] = array[0] - engineState[0];
+		engineState[2] = array[5] - engineState[5];
+		engineState[3] = array[10] - engineState[10];
+		engineState[4] = array[15] - engineState[15];
+		engineState[11] = array[6] - engineState[6];
+		engineState[12] = array[7] - engineState[7];
+		engineState[13] = array[8] - engineState[8];
+		engineState[14] = array[9] - engineState[9];
+		Pack.LE_To_UInt32(ivBytes, 16, engineState, 6, 2);
+	}
+}