From 73d48d25f3cb9b4829874bea2eace55526c18757 Mon Sep 17 00:00:00 2001
From: Kevin Jones <kevin@vcsjones.com>
Date: Fri, 26 Jun 2026 21:58:05 -0400
Subject: [PATCH] Improve AES-KWP for Windows

---
 .../src/System/Security/Cryptography/Aes.cs   | 14 ++----
 .../Cryptography/AesImplementation.Windows.cs | 49 +++++++++++++++++++
 2 files changed, 53 insertions(+), 10 deletions(-)

diff --git a/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/Aes.cs b/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/Aes.cs
index 2f07e043fa6a3d..45436e08e799d2 100644
--- a/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/Aes.cs
+++ b/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/Aes.cs
@@ -365,7 +365,7 @@ private protected int DecryptKeyWrapPaddedCore<TState>(
             ReadOnlySpan<byte> source,
             Span<byte> destination,
             TState state,
-            KeyWrapEcbTransform<TState> decryptEcb)
+            Func<TState, ReadOnlySpan<byte>, Span<byte>, int> decryptEcb)
         {
             ulong iv;
 
@@ -429,17 +429,11 @@ protected virtual unsafe void EncryptKeyWrapPaddedCore(ReadOnlySpan<byte> source
                 this,
                 static (instance, source, destination) => instance.EncryptEcb(source, destination, PaddingMode.None));
         }
-
-        private protected delegate int KeyWrapEcbTransform<TState>(
-            TState state,
-            ReadOnlySpan<byte> source,
-            Span<byte> destination);
-
         private protected void EncryptKeyWrapPaddedCore<TState>(
             ReadOnlySpan<byte> source,
             Span<byte> destination,
             TState state,
-            KeyWrapEcbTransform<TState> encryptEcb)
+            Func<TState, ReadOnlySpan<byte>, Span<byte>, int> encryptEcb)
         {
             Debug.Assert(destination.Length == GetKeyWrapPaddedLength(source.Length));
 
@@ -491,7 +485,7 @@ private void Rfc3394Wrap<TState>(
             ReadOnlySpan<byte> source,
             Span<byte> destination,
             TState state,
-            KeyWrapEcbTransform<TState> encryptEcb)
+            Func<TState, ReadOnlySpan<byte>, Span<byte>, int> encryptEcb)
         {
             Debug.Assert(source.Length % 8 == 0);
             Debug.Assert(source.Length >= 16);
@@ -530,7 +524,7 @@ private ulong Rfc3394Unwrap<TState>(
             ReadOnlySpan<byte> source,
             Span<byte> destination,
             TState state,
-            KeyWrapEcbTransform<TState> decryptEcb)
+            Func<TState, ReadOnlySpan<byte>, Span<byte>, int> decryptEcb)
         {
             Span<byte> B = stackalloc byte[16];
             Span<byte> A = B.Slice(0, 8);
diff --git a/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesImplementation.Windows.cs b/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesImplementation.Windows.cs
index 77dc9472650892..2e2cd0e646f7c7 100644
--- a/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesImplementation.Windows.cs
+++ b/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesImplementation.Windows.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
 using Internal.Cryptography;
 using Internal.NativeCrypto;
 
@@ -44,5 +45,53 @@ private static BasicSymmetricCipherLiteBCrypt CreateLiteCipher(
                 iv,
                 encrypting);
         }
+
+        protected override void EncryptKeyWrapPaddedCore(ReadOnlySpan<byte> source, Span<byte> destination)
+        {
+            Debug.Assert(destination.Length == GetKeyWrapPaddedLength(source.Length));
+
+            ILiteSymmetricCipher cipher = GetKey().UseKey(
+                BlockSize / BitsPerByte,
+                static (blockSizeBytes, key) => CreateLiteCipher(
+                    CipherMode.ECB,
+                    key,
+                    iv: default,
+                    blockSize: blockSizeBytes,
+                    paddingSize: blockSizeBytes,
+                    feedbackSize: 0,
+                    encrypting: true));
+
+            using (cipher)
+            {
+                EncryptKeyWrapPaddedCore(
+                    source,
+                    destination,
+                    cipher,
+                    static (cipher, source, destination) => cipher.Transform(source, destination));
+            }
+        }
+
+        protected override int DecryptKeyWrapPaddedCore(ReadOnlySpan<byte> source, Span<byte> destination)
+        {
+            ILiteSymmetricCipher cipher = GetKey().UseKey(
+                BlockSize / BitsPerByte,
+                static (blockSizeBytes, key) => CreateLiteCipher(
+                    CipherMode.ECB,
+                    key,
+                    iv: default,
+                    blockSize: blockSizeBytes,
+                    paddingSize: blockSizeBytes,
+                    feedbackSize: 0,
+                    encrypting: false));
+
+            using (cipher)
+            {
+                return DecryptKeyWrapPaddedCore(
+                    source,
+                    destination,
+                    cipher,
+                    static (cipher, source, destination) => cipher.Transform(source, destination));
+            }
+        }
     }
 }