Historically people have tended to think .NET is Windows-only and therefore any library built on it is only going to run on Windows. This hasn't been the reality for a few years now and .NET will run mostly anywhere these days. Kerberos.NET will run on any supported .NET Standard 2.0 runtime, which today is Windows, Linux, and Mac OS. The recommended method is using the nuget package.
PM> Install-Package Kerberos.NET
However, there are some important caveats.
The cryptographic primitives used by the Kerberos protocols are available in .NET across all platforms, however there are extensions to the protocol that rely on primitives that are not exposed at the framework level. There are two extensions that do not work for time being:
- RFC 4757: RC4-HMAC -- This would be better described as the MD4/RC4/HMACMD5 suite. It's the defacto suite introduced in Windows 2000 for compatibility reasons and has since been deprecated by the standards bodies. The MD4 hash is not exposed through .NET (for good reason) and must be P/Invoke'd or written in managed code. It's not a particularly complicated hashing algorithm, but it's also not worth taking on for the sake of cross-platform support. You're not affected in any way if you're using AES (as you should be).
- RFC 4556: PKINIT -- This relies on a Diffie-Hellman key agreement, which is also not exposed through .NET (also for good reason). This is somewhat more problematic because it's an important extension and should be supported everywhere. It's not a particularly complicated algorithm and in fact there's a poorly written implemention in the test harness. This needs to be better before it would be considered for library support. This might also be moot once Elliptic Curve support is added.
Adding Your own Cryptographic Implementation
If you're so inclined and need either of the above two extensions you can bring your own implementation by registering your own platform layer:
CryptoPal.RegisterPal(() => new MyCustomCryptoPalImplementation());
It needs to be called before any crypto calls occur, otherwise you're going to defaulted to the existing platform implementation.
DNS Resolution Support
Kerberos relies on DNS for resolving KDC locations by checking for SRV records of the Kerberos service at
_kerberos.tcp.realm.net (or UDP). This is necessary if you don't know the location of the KDC you're needing to authenticate against. Unfortunately .NET doesn't expose a way to query SRV records, and the library relies on P/Invoke into the Windows DnsQuery_W function to do this.
You can bring your own DNS support on other platforms by creating a class that implements
IKerberosDnsQuery. A functional implementation that works on other platforms can be found in the Bruce project: Kerberos.NET/PlatformIndependentDnsClient.cs at develop · dotnet/Kerberos.NET (github.com).
The unit tests are inherently Windows-centric and P/Invoke for a myriad of interop and compatibility reasons. This isn't a problem for developers just grabbing the nuget package, but it is a bit problematic for anyone wanting to extend the library or fix the above limitations on non-Windows platforms. Eventually the tests may be reorganized and tagged as platform-specific, but that's not a high priority at the moment.