Add hadamard utilities to encode keys

Add the utility functions to encode & decode 32 bytes keys. The
hadamard encoding will expand a 2 bytes word to 2^15 bits. And thus the
32 byte key will expand to 64KiB in space. The encoded value is more
robust and we will be able to recover the key even if there is some
corruption.

Test: unittest pass
Change-Id: Iae8a28a8c7c1699f8641f9250f0eccde5c2ff138