diff --git a/Dalamud.Bootstrap/SqexArg/EncryptedArgument.cs b/Dalamud.Bootstrap/SqexArg/EncryptedArgument.cs
new file mode 100644
index 000000000..54b449d86
--- /dev/null
+++ b/Dalamud.Bootstrap/SqexArg/EncryptedArgument.cs
@@ -0,0 +1,148 @@
+using System;
+using System.Buffers;
+using System.Buffers.Text;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Text.RegularExpressions;
+using Dalamud.Bootstrap.Crypto;
+
+namespace Dalamud.Bootstrap.SqexArg
+{
+    internal sealed class EncryptedArgument : IDisposable
+    {
+        private static char[] ChecksumTable = new char[]
+        {
+            'f', 'X', '1', 'p', 'G', 't', 'd', 'S',
+            '5', 'C', 'A', 'P', '4', '_', 'V', 'L'
+        };
+
+        /// <summary>
+        /// Denotes that no checksum is encoded.
+        /// </summary>
+        private const char NoChecksumMarker = '!';
+
+        /// <summary>
+        /// A data that is not encrypted.
+        /// </summary>
+        private IMemoryOwner<byte> m_data;
+
+        /// <summary>
+        /// Creates an object that can take (e.g. /T=1234)
+        /// </summary>
+        /// <param name="data">A data that is not encrypted.</param>
+        /// <remarks>
+        /// This takes the ownership of the data.
+        /// </remarks>
+        public EncryptedArgument(IMemoryOwner<byte> data)
+        {
+            m_data = data;
+        }
+        
+        public EncryptedArgument(string argument)
+        {
+            var buffer = MemoryPool<byte>.Shared.Rent(Encoding.UTF8.GetByteCount(argument));
+            Encoding.UTF8.GetBytes(argument, buffer.Memory.Span);
+
+            m_data = buffer;
+        }
+
+        public void Dispose()
+        {
+            m_data?.Dispose();
+            m_data = null!;
+        }
+
+        /// <summary>
+        /// 
+        /// </summary>
+        /// <param name="argument"></param>
+        /// <param name="payload">An encrypted payload encoded in url-safe base64 string extracted. The value is undefined if the function fails.</param>
+        /// <param name="checksum">A checksum of the key extracted. The value is undefined if the function fails.</param>
+        /// <returns>Returns true on success, false otherwise.</returns>
+        public static bool Extract(string argument, out string payload, out char checksum)
+        {
+            // must start with //**sqex0003, some characters, one checksum character and end with **//
+            var regex = new Regex(@"^\/\/\*\*sqex0003(?<payload>.+)(?<checksum>.)\*\*\/\/$");
+            
+            var match = regex.Match(argument);
+            if (!match.Success)
+            {
+                payload = "";
+                checksum = '\0';
+                return false;
+            }
+
+            payload = match.Groups["payload"].Value;
+            checksum = match.Groups["checksum"].Value[0];
+            return true;
+        }
+
+        public static EncryptedArgument FromEncryptedData(string argument, uint key)
+        {
+            // Create the key
+            Span<byte> keyBytes = stackalloc byte[8];
+            CreateKey(key, keyBytes);
+
+            // Allocate the buffer to store decrypted data
+            var decryptedData = CreateAlignedBuffer(encryptedData.Length);
+            
+            // Decrypt the data with the key
+            try
+            {
+                var blowfish = new Blowfish(keyBytes);
+                blowfish.Decrypt(encryptedData, decryptedData.Memory.Span);
+            }
+            catch (Exception)
+            {
+                decryptedData?.Dispose(); // TODO: clean up this thing?
+                throw;
+            }
+            
+            return new EncryptedArgument(decryptedData);
+        }
+
+        private static IMemoryOwner<byte> CreateAlignedBuffer(int minimumSize)
+        {
+            // align (by padding) to block size if needed
+            throw new NotImplementedException("TODO");
+        }
+
+        /// <summary>
+        /// 
+        /// </summary>
+        /// <param name="decryptedData"></param>
+        /// <returns></returns>
+        private static bool CheckDecryptedData(ReadOnlySpan<byte> decryptedData)
+        {
+            // TODO
+            return false;
+        }
+
+        /// <summary>
+        /// Formats the key.
+        /// </summary>
+        /// <param name="key">A secret key.</param>
+        /// <param name="destination">A buffer where formatted key will be stored. This must be larger than 8 bytes.</param>
+        private static void CreateKey(uint key, Span<byte> destination)
+        {
+            if (!Utf8Formatter.TryFormat(key, destination, out var _, new StandardFormat('x', 8)))
+            {
+                var message = $"BUG: Could not create a key"; // This should not fail but..
+                throw new InvalidOperationException(message);
+            }
+        }
+
+        /// <summary>
+        /// Converts the url-safe variant of base64 string to bytes.
+        /// </summary>
+        /// <param name="payload">A url-safe variant of base64 string.</param>
+        private static byte[] DecodeUrlSafeBase64(string payload)
+        {
+            var base64Str = payload
+                .Replace('-', '+')
+                .Replace('_', '/');
+            
+            return Convert.FromBase64String(base64Str);
+        }
+    }
+}