Strong-name APIs throw PlatformNotSupportedException
A few APIs that aren't supported in .NET/.NET Core but didn't do anything when accessed have been changed to now throw a PlatformNotSupportedException at run time. Previously, using these APIs would eventually result in a run-time exception further along; the exception is now thrown when the type is instantiated or first accessed.
Previous behavior
In previous versions, calling AssemblyName.KeyPair or StrongNameKeyPair(Byte[]) was a no-op. Calling StrongNameKeyPair(FileStream) read the stream but otherwise did nothing.
New behavior
Starting in .NET 6, each of the three affected APIs throws a PlatformNotSupportedException at run time.
Version introduced
.NET 6
Type of breaking change
This change can affect binary compatibility.
Reason for change
Previously, an application that called the API compiled and ran, but as soon as the instance was used in any code path, it threw a run-time exception. To make it more explicit that this scenario is unsupported, the exception-throwing logic was moved into the instance constructor. In case no instances are created, the exception is also thrown in public entry points that return this type, that is, AssemblyName.KeyPair.
Recommended action
Strong-name signing is not supported in .NET/.NET Core, and there is no workaround.
Note
.NET Core/5+ never checks signatures in its runtime. However, if you're targeting cross-platform libraries (for example, a basic auth package that targets .NET Standard 2.0, so it runs on .NET Framework too), then strong-naming is a good idea for cross-runtime compatibility. .NET Framework continues to enforce strong naming if the calling app is strong-named. You can strong-name assemblies in all versions of .NET using the Sn.exe tool. For more information, see Strong name signing.
