baseline: OpenMU upstream b5a0961 (fresh source)

src/Network/Xor/Xor3Encryptor.cs

@@ -0,0 +1,43 @@
+// <copyright file="Xor3Encryptor.cs" company="MUnique">
+// Licensed under the MIT License. See LICENSE file in the project root for full license information.
+// </copyright>
+
+namespace MUnique.OpenMU.Network.Xor;
+
+/// <summary>
+/// An encryptor which XOR-encrypts data using a 3-byte key.
+/// </summary>
+public class Xor3Encryptor : ISpanEncryptor
+{
+    private readonly byte[] _xor3Keys;
+
+    private readonly int _startOffset;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="Xor3Encryptor"/> class.
+    /// </summary>
+    /// <param name="startOffset">The start offset.</param>
+    public Xor3Encryptor(int startOffset)
+    {
+        this._startOffset = startOffset;
+        this._xor3Keys = DefaultKeys.Xor3Keys;
+    }
+
+    /// <inheritdoc/>
+    public void Encrypt(Span<byte> data)
+    {
+        this.InternalEncrypt(data.Slice(this._startOffset));
+    }
+
+    /// <summary>
+    /// Internal encrypt function. XORs each byte with one byte of the 3-byte key.
+    /// </summary>
+    /// <param name="data">The data.</param>
+    protected void InternalEncrypt(Span<byte> data)
+    {
+        for (var i = 0; i < data.Length; i++)
+        {
+            data[i] ^= this._xor3Keys[i % 3];
+        }
+    }
+}