C#: How to load a private key into RsaSecurityKey in .net Framework/Standard?

Question

I need to generate an RsaSecurityKey with a private key to sign a JWT.

I have code working in net5.0 but I need that code to work in a .net Standard/Framework library.

Here is the working code:

        private static RsaSecurityKey GetRsaKey(byte[] privateKey)
        {
            using RSACryptoServiceProvider rsa = new RSACryptoServiceProvider(2048);

            rsa.ImportRSAPrivateKey(new ReadOnlySpan<byte>(privateKey), out int _);
            RSAParameters @params = rsa.ExportParameters(true);

            return new RsaSecurityKey(@params);
        }

Unfortunately, rsa.ImportRSAPrivateKey is not available in .net Standard.

I have not been able to find how to replace that piece.

Would anyone know how we are meant to do that with .net Framework?

Thank you.

Answer 1

The following code works in .net 4.0 and higher. I had the same requirement the code uses bouncycastle and jose.jwt from nuget to generate a jwt.

This is the code fragment I found and tested it works.

GIT Link

In the main function

claims2 gives you back the json payload you passed

jwt = token

you can test it on jwt.io put the jwt in the section and the bottom paste the public and private.

If it is a valid signature will be valid

claims is the payload.

Hope this helps you