R0912: Too many branches (15/12) (too-many-branches) in verify_hash

[ross-spencer]

This should be easily fixable with some more discrete functions. Make this a priority to look at with the unit tests largely all in place.

[ross-spencer]

NB. wrap R0915: Too many statements (71/50) (too-many-statements) into this as well. And double check how this is measured in pylint.