GEMSTASH-194 Support for FIPS Mode

[ayohrling]

This updates the digest usage from MD5 to SHA256 to support hosts that are
configured in FIPS mode.

Fixes #194

[olleolleolle]

If I understand this correctly, this change modifies the directory names for Storage's "Resources" (aka uploaded things).

That would be a breaking change, right?

[ayohrling]

Yes, it changes the hashing mechanism used in the storage structure to a FIPS-compliant cipher. It will break any cached resources from older versions. Upgraded systems would need to re-cache. A conversion really wouldn't be possible, because we'd be guessing at rolling back from safe_name to name with regards to casing.

[bronzdoc]

Maybe add this as a flag at the moment and make it the default in a major version.

[olleolleolle]

To suggest a flag name, I read a bit about the "FIPS mode" concept.

I like the MS registry key name best: FipsAlgorithmPolicy.

It describes what we do to Gemstash when this new option is set. We choose crypto in FIPS-compliant ways.

As an option name --use-fips-algorithm-policy (default: false).

What are some better flag names?

[bronzdoc]

@olleolleolle what about --fips and have what it does in the description?

[olleolleolle]

I added a PR on top of the @ayohrling one.