Hi,

Short answer is that most likely it is not possible and/or anyway goes beyond what the SDK supports currently.

Basically anything that contains “sun.security” is not considered supported (might still work, but we wont test). Certificate operations should mostly be done via the CryptoProvider and CertificateProvider implementations (SDK has for Bouncy/SpongyCastle) and/or via the utils CryptoUtil/CertificateUtils (that use those providers).

If that privatekey does not implement java.security.interfaces.RSAPrivateKey it probably wont work (if it would, you could cast+pass it to the public PrivKey(RSAPrivateKey privateKey)). You could try to see if you can get the encoded format of the private key via .getEncoded and pass it to public PrivKey(byte[] encodedPrivateKey). However assuming this based on a quick google search https://github.com/frohoff/jdk8u-dev-jdk/blob/master/src/windows/classes/sun/security/mscapi/Key.java would return null and that your key class doesn’t implement the java.security.interfaces.RSAPrivateKey. Generally I would assume the MS keystore to be designed as such that the private key is not directly accessible. That wont work with the SDK as it is; we need the key data in entirely as the data is passed to BouncyCastle lib for crypto operations (in the normal case).

The crypto abstractions could maybe use some more work in the future, but I’m not yet sure when that will happen. At some point we will need to add support for ECC keys; I could see the APIs changing then a bit so we could then check if this could be also improved.