Yup I tried casting but those two are from diffrent packages. Key is from Dogtag and privateKey is from Mozilla. Anyway i found solution using pkcs11 crypto token from jss and getBytes from Key object( I don't have access to code, and don't remember method name) 

Really appreciate Your help John

On Monday, 26 October 2015, John Magne <jmagne@redhat.com> wrote:
Look in RecoveryService.java , method something like createPFX if still want to pursue that angle.
As for the PrivateKeyObject I will have to look around to refresh memory, but have tried casting?

----- Original Message -----
> From: "Marcin Mierzejewski" <marcinmierzejewski1024@gmail.com>
> To: "John Magne" <jmagne@redhat.com>
> Cc: pki-users@redhat.com
> Sent: Monday, 26 October, 2015 10:40:53 AM
> Subject: Re: [Pki-users] Export keyPair and certificate to .p12 (private key with certificate) and .der (public key
> and certificate)
> All I found in KraClient is a KeyClient which role in retriving process is
> limited to returning some generic "Key" object. I would love some "find
> usages" that works across group of jars to find out where that recovering
> is.
> In meantime I refactor PKCS12Export to get that working, but propably it
> could be done better. Now what is the problem, how to change the "Key"
> object to some object that implements org.mozzlila.PrivateKey ? I checked
> all this privatekey classes and any of this had a public constructor or
> builder with rawdata(byte[]) and mozilla jss documentation sucks.
> 2015-10-26 18:21 GMT+01:00 John Magne <jmagne@redhat.com>:
> > Take a look in the KRA code, which does this when recovering keys back to
> > the user.
> >
> > ----- Original Message -----
> > From: "Marcin Mierzejewski" <marcinmierzejewski1024@gmail.com>
> > To: pki-users@redhat.com
> > Sent: Saturday, October 24, 2015 10:49:15 AM
> > Subject: [Pki-users] Export keyPair and certificate to .p12 (private key
> > with certificate) and .der (public key and certificate)
> >
> > After creation certficate in application I have to return a certificate
> > with private key. That file could be in .p12 format, am I right? Can I
> > found example of create that file in existing code?
> > there is a PKCS12Export command line tool but it propably works with
> > existing creditentials on nssdatabase. Eventually I can get code from
> > PKCS12Export and make addKeyBag() and few other methods public. Ok soo i
> > have first part.
> > And second part .der file is the same as certificate.getEncoded() if yes,
> > thats allready done^^
> >
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