Use native AesGcm for .NET Framework from nuget

Author: scott-xu

Directory.Packages.props

@@ -12,6 +12,7 @@
     <PackageVersion Include="Meziantou.Analyzer" Version="2.0.201" />
 
     <!-- Should stay on LTS .NET releases. -->
+    <PackageVersion Include="Microsoft.Bcl.Cryptography" Version="10.0.0-preview.5.25277.114" />
     <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="8.0.3" />
     <PackageVersion Include="Microsoft.Extensions.Logging.Console" Version="9.0.5" />
     <PackageVersion Include="MSTest" Version="3.9.1" />

src/Renci.SshNet/Renci.SshNet.csproj

@@ -49,7 +49,11 @@
     </PackageReference>
   </ItemGroup>
 
-  <ItemGroup Condition=" !$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net8.0')) ">
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net462' ">
+    <PackageReference Include="Microsoft.Bcl.Cryptography" />
+  </ItemGroup>
+
+  <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
     <PackageReference Include="System.Formats.Asn1" />
   </ItemGroup>
 

src/Renci.SshNet/Security/Cryptography/Ciphers/AesGcmCipher.BclImpl.cs

@@ -1,4 +1,4 @@
-#if NET
+#if !NETSTANDARD
 using System;
 using System.Security.Cryptography;
 

src/Renci.SshNet/Security/Cryptography/Ciphers/AesGcmCipher.cs

@@ -15,7 +15,7 @@ internal sealed partial class AesGcmCipher : SymmetricCipher, IDisposable
         private const int TagSizeInBytes = 16;
         private readonly byte[] _iv;
         private readonly int _aadLength;
-#if NET
+#if !NETSTANDARD
         private readonly Impl _impl;
 #else
         private readonly BouncyCastleImpl _impl;
@@ -62,10 +62,18 @@ public AesGcmCipher(byte[] key, byte[] iv, int aadLength)
             // SSH AES-GCM requires a 12-octet Initial IV
             _iv = iv.Take(12);
             _aadLength = aadLength;
-#if NET
+#if !NETSTANDARD
             if (System.Security.Cryptography.AesGcm.IsSupported)
             {
-                _impl = new BclImpl(key, _iv);
+                try
+                {
+                    _impl = new BclImpl(key, _iv);
+                }
+                catch (DllNotFoundException)
+                {
+                    // Mono doesn't have BCrypt.dll
+                    _impl = new BouncyCastleImpl(key, _iv);
+                }
             }
             else
 #endif