How do I create/export to a .PVK file using C#?

Question

I have an RSA private key loaded in an RSACryptoServiceProvider object. I need to export this to a .pvk file for use with SQL Server.

Is there a way to do this from within c#? I see it's possible using openssl... https://stackoverflow.com/a/51207929/5924962

This is the only documentation I could find on the pvk file format: https://web.archive.org/web/20141117214716/http://www.drh-consultancy.demon.co.uk/pvk.html

Answer 1

Mono project has an open source implementation of the PVK format,

https://github.com/mono/mono/blob/master/mcs/class/Mono.Security/Mono.Security.Authenticode/PrivateKey.cs

Note the Mono.Security NuGet package is not official.

Answer 2

If you look at the output of RSACryptoServiceProvider.ExportCspBlob you'll see that it starts with the same sequence of bytes as offset 24 of an unencrypted PVK file. So a PVK file is just the CSP blob with a header:

using (var output = new BinaryWriter(File.Create("rsa.pvk")))
{
    output.Write(0xB0B5F11Eu);  // PVK magic number
    output.Write(0u);
    output.Write(1u);           // KEYTYPE_KEYX for RSA
    output.Write(0u);           // not encrypted
    output.Write(0u);           // encryption salt length

    var cspBlob = rsaCSP.ExportCspBlob(true);
    output.Write((uint)cspBlob.Length);
    output.Write(cspBlob);
}

I've verified that OpenSSL will read this

openssl rsa -in rsa.pvk -inform PVK

and will generate the same PEM private key export as the code in this answer that generates the PEM private key directly from the RSACryptoServiceProvider.