Allocate the buffer at once

Dalamud.Bootstrap/SqexArg/EncryptedArgumentExtensions.cs

@@ -1,20 +1,25 @@
 using System;
 using System.Buffers;
 using System.Buffers.Text;
+using System.Text;
 using Dalamud.Bootstrap.Crypto;
 
 namespace Dalamud.Bootstrap.SqexArg
 {
     internal static class EncryptedArgumentExtensions
     {
-        public static void Decrypt(this EncryptedArgument argument, uint key)
+        public static string Decrypt(this EncryptedArgument argument, uint key)
         {
             Span<byte> keyBytes = stackalloc byte[8];
             CreateKey(key, keyBytes);
 
+            var encryptedData = DecodeDataString(argument.Data, out var encryptedDataLength);
+            var decryptedData = new byte[encryptedData.Length];
+
             var blowfish = new Blowfish(keyBytes);
-            
+            blowfish.Decrypt(encryptedData, decryptedData);
-            
+
+            return Encoding.UTF8.GetString(decryptedData[..encryptedDataLength]);
         }
 
         /// <summary>
@@ -31,24 +36,30 @@ namespace Dalamud.Bootstrap.SqexArg
         }
 
         /// <summary>
-        /// Converts the url-safe variant of base64 string to bytes.
+        /// Converts the data string to bytes. It also allocates more bytes than actual data contained in base64 string for Blowfish.
         /// </summary>
         /// <param name="payload">A url-safe variant of base64 string.</param>
-        private static byte[] DecodeUrlSafeBase64(string payload)
+        /// <param name="payload">A data length that is actually written to the buffer.</param>
+        private static byte[] DecodeDataString(string payload, out int dataLength)
         {
             var base64Str = payload
                 .Replace('-', '+')
                 .Replace('_', '/');
 
-            try
+            // base64: 3 bytes per 4 characters
+            dataLength = (payload.Length / 4) * 3;
+
+            // round to next mutliple of block size which is what Blowfish can process. (i.e. 8 bytes)
+            var alignedLength = (dataLength + (Blowfish.BlockSize - 1)) & (-Blowfish.BlockSize);
+
+            var buffer = new byte[alignedLength];
+
+            if (!Convert.TryFromBase64String(base64Str, buffer, out var _))
             {
-                return Convert.FromBase64String(base64Str);
+                throw new SqexArgException($"A payload {payload} does not look like a valid encrypted argument.");
-            }
-            catch (FormatException ex)
-            {
-                // This is expected to happen if the argument is ill-formed
-                throw new SqexArgException($"A payload {payload} does not look like a valid encrypted argument.", ex);
             }
+
+            return buffer;
         }
 
         private static string EncodeUrlSafeBase64(byte[] payload)
@@ -58,7 +69,6 @@ namespace Dalamud.Bootstrap.SqexArg
             return payloadStr
                 .Replace('+', '-')
                 .Replace('/', '_');
-
         }
     }
 }