Implement AES-GCM with CryptoKit on macOS

With this change, GCM on macOS no longer uses OpenSSL, but routes into the CryptoKit library. This means that tags 12-15 bytes long are no longer supported on macOS.
dotnet · Nov 8, 2022 · e029499 · e029499
1 parent 1f7e169
commit e029499
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Showing 12 changed files with 383 additions and 40 deletions.
diff --git a/...ibraries/Common/src/Interop/OSX/System.Security.Cryptography.Native.Apple/Interop.Aead.cs b/...ibraries/Common/src/Interop/OSX/System.Security.Cryptography.Native.Apple/Interop.Aead.cs
@@ -87,6 +87,82 @@ internal static unsafe void ChaCha20Poly1305Decrypt(
             }
         }
 
+        internal static unsafe void AesGcmEncrypt(
+            ReadOnlySpan<byte> key,
+            ReadOnlySpan<byte> nonce,
+            ReadOnlySpan<byte> plaintext,
+            Span<byte> ciphertext,
+            Span<byte> tag,
+            ReadOnlySpan<byte> aad)
+        {
+            fixed (byte* keyPtr = key)
+            fixed (byte* noncePtr = nonce)
+            fixed (byte* plaintextPtr = plaintext)
+            fixed (byte* ciphertextPtr = ciphertext)
+            fixed (byte* tagPtr = tag)
+            fixed (byte* aadPtr = aad)
+            {
+                const int Success = 1;
+                int result = AppleCryptoNative_AesGcmEncrypt(
+                    keyPtr, key.Length,
+                    noncePtr, nonce.Length,
+                    plaintextPtr, plaintext.Length,
+                    ciphertextPtr, ciphertext.Length,
+                    tagPtr, tag.Length,
+                    aadPtr, aad.Length);
+
+                if (result != Success)
+                {
+                    Debug.Assert(result == 0);
+                    CryptographicOperations.ZeroMemory(ciphertext);
+                    CryptographicOperations.ZeroMemory(tag);
+                    throw new CryptographicException();
+                }
+            }
+        }
+
+        internal static unsafe void AesGcmDecrypt(
+            ReadOnlySpan<byte> key,
+            ReadOnlySpan<byte> nonce,
+            ReadOnlySpan<byte> ciphertext,
+            ReadOnlySpan<byte> tag,
+            Span<byte> plaintext,
+            ReadOnlySpan<byte> aad)
+        {
+            fixed (byte* keyPtr = key)
+            fixed (byte* noncePtr = nonce)
+            fixed (byte* ciphertextPtr = ciphertext)
+            fixed (byte* tagPtr = tag)
+            fixed (byte* plaintextPtr = plaintext)
+            fixed (byte* aadPtr = aad)
+            {
+                const int Success = 1;
+                const int AuthTagMismatch = -1;
+                int result = AppleCryptoNative_AesGcmDecrypt(
+                    keyPtr, key.Length,
+                    noncePtr, nonce.Length,
+                    ciphertextPtr, ciphertext.Length,
+                    tagPtr, tag.Length,
+                    plaintextPtr, plaintext.Length,
+                    aadPtr, aad.Length);
+
+                if (result != Success)
+                {
+                    CryptographicOperations.ZeroMemory(plaintext);
+
+                    if (result == AuthTagMismatch)
+                    {
+                        throw new AuthenticationTagMismatchException();
+                    }
+                    else
+                    {
+                        Debug.Assert(result == 0);
+                        throw new CryptographicException();
+                    }
+                }
+            }
+        }
+
         [LibraryImport(Libraries.AppleCryptoNative)]
         private static unsafe partial int AppleCryptoNative_ChaCha20Poly1305Encrypt(
             byte* keyPtr,
@@ -116,5 +192,35 @@ private static unsafe partial int AppleCryptoNative_ChaCha20Poly1305Decrypt(
             int plaintextLength,
             byte* aadPtr,
             int aadLength);
+
+        [LibraryImport(Libraries.AppleCryptoNative)]
+        private static unsafe partial int AppleCryptoNative_AesGcmEncrypt(
+            byte* keyPtr,
+            int keyLength,
+            byte* noncePtr,
+            int nonceLength,
+            byte* plaintextPtr,
+            int plaintextLength,
+            byte* ciphertextPtr,
+            int ciphertextLength,
+            byte* tagPtr,
+            int tagLength,
+            byte* aadPtr,
+            int aadLength);
+
+        [LibraryImport(Libraries.AppleCryptoNative)]
+        private static unsafe partial int AppleCryptoNative_AesGcmDecrypt(
+            byte* keyPtr,
+            int keyLength,
+            byte* noncePtr,
+            int nonceLength,
+            byte* ciphertextPtr,
+            int ciphertextLength,
+            byte* tagPtr,
+            int tagLength,
+            byte* plaintextPtr,
+            int plaintextLength,
+            byte* aadPtr,
+            int aadLength);
     }
 }
diff --git a/src/libraries/System.Security.Cryptography/src/System.Security.Cryptography.csproj b/src/libraries/System.Security.Cryptography/src/System.Security.Cryptography.csproj
@@ -783,6 +783,7 @@
              Link="Common\System\Text\UrlBase64Encoding.cs" />
     <Compile Include="$(CommonPath)System\Text\ValueUtf8Converter.cs"
              Link="Common\System\Text\ValueUtf8Converter.cs" />
+    <Compile Include="System\Security\Cryptography\AesGcm.OpenSsl.cs" />
     <Compile Include="System\Security\Cryptography\AesImplementation.OpenSsl.cs" />
     <Compile Include="System\Security\Cryptography\AsnFormatter.OpenSsl.cs" />
     <Compile Include="System\Security\Cryptography\CapiHelper.DSA.Shared.cs" />
@@ -870,7 +871,6 @@
     <Compile Include="$(CommonPath)Microsoft\Win32\SafeHandles\SafeEvpCipherCtxHandle.Unix.cs"
              Link="Common\Microsoft\Win32\SafeHandles\SafeEvpCipherCtxHandle.Unix.cs" />
     <Compile Include="System\Security\Cryptography\AesCcm.OpenSsl.cs" />
-    <Compile Include="System\Security\Cryptography\AesGcm.OpenSsl.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(UseAndroidCrypto)' == 'true'">
     <Compile Include="$(CommonPath)Interop\Android\Interop.JObjectLifetime.cs"
@@ -1292,6 +1292,7 @@
              Link="Common\System\Security\Cryptography\RSASecurityTransforms.macOS.cs" />
     <Compile Include="$(CommonPath)System\Security\Cryptography\RSAOpenSsl.cs"
              Link="Common\System\Security\Cryptography\RSAOpenSsl.cs" />
+    <Compile Include="System\Security\Cryptography\AesGcm.macOS.cs" />
     <Compile Include="System\Security\Cryptography\ChaCha20Poly1305.macOS.cs" />
     <Compile Include="System\Security\Cryptography\DSA.Create.SecurityTransforms.cs" />
     <Compile Include="System\Security\Cryptography\DSACryptoServiceProvider.Unix.cs" />

diff --git a/...libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.Android.cs b/...libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.Android.cs
@@ -12,6 +12,7 @@ public sealed partial class AesGcm
         private SafeEvpCipherCtxHandle _ctxHandle;
 
         public static bool IsSupported => true;
+        public static KeySizes TagByteSizes { get; } = new KeySizes(12, 16, 1);
 
         [MemberNotNull(nameof(_ctxHandle))]
         private void ImportKey(ReadOnlySpan<byte> key)

diff --git a/...ries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.NotSupported.cs b/...ries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.NotSupported.cs
@@ -8,6 +8,7 @@ namespace System.Security.Cryptography
     public partial class AesGcm
     {
         public static bool IsSupported => false;
+        public static KeySizes TagByteSizes { get; } = new KeySizes(12, 16, 1);
 
 #pragma warning disable CA1822, IDE0060
         private void ImportKey(ReadOnlySpan<byte> key)

diff --git a/...libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.OpenSsl.cs b/...libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.OpenSsl.cs
@@ -12,6 +12,7 @@ public sealed partial class AesGcm
         private SafeEvpCipherCtxHandle _ctxHandle;
 
         public static bool IsSupported { get; } = Interop.OpenSslNoInit.OpenSslIsAvailable;
+        public static KeySizes TagByteSizes { get; } = new KeySizes(12, 16, 1);
 
         [MemberNotNull(nameof(_ctxHandle))]
         private void ImportKey(ReadOnlySpan<byte> key)

diff --git a/...libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.Windows.cs b/...libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.Windows.cs
@@ -12,6 +12,7 @@ public partial class AesGcm
         private SafeKeyHandle _keyHandle;
 
         public static bool IsSupported => true;
+        public static KeySizes TagByteSizes { get; } = new KeySizes(12, 16, 1);
 
         [MemberNotNull(nameof(_keyHandle))]
         private void ImportKey(ReadOnlySpan<byte> key)

diff --git a/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.cs b/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.cs
@@ -13,7 +13,6 @@ public sealed partial class AesGcm : IDisposable
     {
         private const int NonceSize = 12;
         public static KeySizes NonceByteSizes { get; } = new KeySizes(NonceSize, NonceSize, 1);
-        public static KeySizes TagByteSizes { get; } = new KeySizes(12, 16, 1);
 
         public AesGcm(ReadOnlySpan<byte> key)
         {

diff --git a/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.macOS.cs b/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/AesGcm.macOS.cs
@@ -0,0 +1,77 @@
+// 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 System.Diagnostics.CodeAnalysis;
+using Microsoft.Win32.SafeHandles;
+
+namespace System.Security.Cryptography
+{
+    public sealed partial class AesGcm
+    {
+        private byte[]? _key;
+
+        // CryptoKit added AES.GCM in macOS 10.15, which is our minimum target for macOS.
+        public static bool IsSupported => true;
+
+        // CryptoKit only supports 16 byte tags.
+        public static KeySizes TagByteSizes { get; } = new KeySizes(16, 16, 1);
+
+        [MemberNotNull(nameof(_key))]
+        private void ImportKey(ReadOnlySpan<byte> key)
+        {
+            // We should only be calling this in the constructor, so there shouldn't be a previous key.
+            Debug.Assert(_key is null);
+
+            // Pin the array on the POH so that the GC doesn't move it around to allow zeroing to be more effective.
+            _key = GC.AllocateArray<byte>(key.Length, pinned: true);
+            key.CopyTo(_key);
+        }
+
+        private void EncryptCore(
+            ReadOnlySpan<byte> nonce,
+            ReadOnlySpan<byte> plaintext,
+            Span<byte> ciphertext,
+            Span<byte> tag,
+            ReadOnlySpan<byte> associatedData)
+        {
+            CheckDisposed();
+            Interop.AppleCrypto.AesGcmEncrypt(
+                _key,
+                nonce,
+                plaintext,
+                ciphertext,
+                tag,
+                associatedData);
+        }
+
+        private void DecryptCore(
+            ReadOnlySpan<byte> nonce,
+            ReadOnlySpan<byte> ciphertext,
+            ReadOnlySpan<byte> tag,
+            Span<byte> plaintext,
+            ReadOnlySpan<byte> associatedData)
+        {
+            CheckDisposed();
+            Interop.AppleCrypto.AesGcmDecrypt(
+                _key,
+                nonce,
+                ciphertext,
+                tag,
+                plaintext,
+                associatedData);
+        }
+
+        public void Dispose()
+        {
+            CryptographicOperations.ZeroMemory(_key);
+            _key = null;
+        }
+
+        [MemberNotNull(nameof(_key))]
+        private void CheckDisposed()
+        {
+            ObjectDisposedException.ThrowIf(_key is null, this);
+        }
+    }
+}