Change encArg impl

Dalamud.Bootstrap/SqexArg/EncryptedArgumentExtensions.cs

@@ -0,0 +1,64 @@
+using System;
+using System.Buffers;
+using System.Buffers.Text;
+using Dalamud.Bootstrap.Crypto;
+
+namespace Dalamud.Bootstrap.SqexArg
+{
+    internal static class EncryptedArgumentExtensions
+    {
+        public static void Decrypt(this EncryptedArgument argument, uint key)
+        {
+            Span<byte> keyBytes = stackalloc byte[8];
+            CreateKey(key, keyBytes);
+
+            var blowfish = new Blowfish(keyBytes);
+            
+            
+        }
+
+        /// <summary>
+        /// Formats a 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)))
+            {
+                throw new InvalidOperationException("BUG: Could not create a key");
+            }
+        }
+
+        /// <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('_', '/');
+
+            try
+            {
+                return Convert.FromBase64String(base64Str);
+            }
+            catch (FormatException ex)
+            {
+                // This is expected to happen if the argument is ill-formed
+                throw new SqexArgException($"A payload {payload} does not look like a valid encrypted argument.", ex);
+            }
+        }
+
+        private static string EncodeUrlSafeBase64(byte[] payload)
+        {
+            var payloadStr = Convert.ToBase64String(payload);
+
+            return payloadStr
+                .Replace('+', '-')
+                .Replace('/', '_');
+
+        }
+    }
+}