The SecureBlackbox assemblies are specific to each platform and use platform-specific features and quirks. It is not technically possible (at least without some serious compromises) to create a PCL version of the SecureBlackbox assemblies (and a PCL version of your code that would use such PCL assemblies). Also, the base PCL library is very limited, without socket support and some other features, so even if SecureBlackbox were offered for PCL, it would be severely feature-limited.