Implement Hierarchical Identity Based Encryption

[ldub]

Part of my work for Ocelot included researching an HIBE-like system for managing keys and permissions.

I used pairings.py's bn256 curve code to implement the Setup, KeyGen, Encrypt, and Decrypt functions from Dan Boneh's HIBE paper, available here: https://crypto.stanford.edu/~dabo/papers/shibe.pdf. These functions currently work as desired but require further effort to encode arbitrary messages as pairings on the curve.

We decided to contribute this code into your repo because you actually have a TODO item specifically for implementing IBE.