Play Integrity local verification

I am trying to integrate the play integrity check in my app to make sure that my app is not installed on a rooted Android device. I can successfully obtain the integrity token response as guided in the google document. But I am trying to verify it in my locally and close the app if its installed on a rooted device. For that local verification, I am following the document Decrypt and verify locally. But I could not understand what is Base64OfEncodedDecryptionKey and Base64OfEncodedVerificationKey and from where I can obtain that.