Enforce stronger constraints on the types of pk_d, ak, nk, cv, epk, and rk, and ensure esk is not zero when encrypting.
Enforce stronger constraints on the types of pk_d, ak, nk, cv, epk, and rk, and ensure esk is not zero when encrypting.

Signed-off-by: Daira Hopwood <cd7d43d5556a38ce626d53826fddc46adc597539@jacaranda.org>

zcash/zips,zcash/zips,zcash/zips,zcash/zips