How to import PKCS#8 RSA privateKey (created by OpenSSL) in C#

Question

I'm trying to find a way to read a privateKey created using OpenSSL PKCS#8 RSA in C# without use external library.

Someone know how can i do this?

Answer 1

The easiest way to do this with an external library, is using the (free) Chillkat Public / Private Key Component: using that, importing the key can be done using just a few lines of code and if you're willing to pay the $149 or so for the rest of the library, it will make dealing with general crypto concepts a lot easier as well.

And unlike the regular Microsoft .NET Framework, the Mono project does seem to have a PKCS8 implementation for which the full C# source is available. This may be suitable as a starting point in case you absolutely cannot rely on external libraries, assuming the (LGPL 2.0) license associated with the Mono code works for you...

Finally, the PKCS #8 format is not too difficult to parse, and the RSA/DSA key pair objects are as per PKCS #11 and relatively easy to convert to a .NET X509Certificate once you figure out where all the bits go -- I actually did this in VB.NET a while ago, but unfortunately am not able to share that code.

Answer 2

Thanks for your answer.

My script to create RSA key i used OpenSSL whit:

(Linux Script)

openssl genrsa -out ${NAME}_openssl.key 2048 openssl pkcs8 -topk8 -in ${NAME}_openssl.key -nocrypt > ${NAME}.key openssl req -new -x509 -key ${NAME}.key -out ${NAME}.crt -outform DER

In C# we need privateKey in XML format. I used this parser to do this.

To decrypt de challenge we need to use:

  byte[] challange = server.getChallenge();

  RSACryptoServiceProvider rsaProvider = new RSACryptoServiceProvider();

  rsaProvider.FromXmlString(Demo.Properties.Resources.XmlPrivateKey);

  byte[] plaintext = rsaProvider.Decrypt(challange, false);

To encrypt whit server certificate we need to use:

  RSACryptoServiceProvider rsaProvider = x509.PublicKey.Key as RSACryptoServiceProvider;

  byte[] answer = RsaProvider.Encrypt(plaintext, false);

Thanks for [JavaScience Consulting][2]