This derives from the reference implementation:

Source: https://github.com/tpoeppelmann/newhope/tree/master/ref at bc06c1ac
Paper: https://eprint.iacr.org/2015/1092

However, it does not interoperate, due to the replacement of SHAKE-128
with AES-CTR (for polynomial generation) and the replacement of SHA-3
with SHA-256 (for key whitening).

Change-Id: I6a55507aea85331245e2fbd41bae5cc049fdca3c
Reviewed-on: https://boringssl-review.googlesource.com/7690
Reviewed-by: Adam Langley <agl@google.com>