Replace md5 with sha512

[vvalouch]

MD5 is not FIPS compliant thus I am proposing replacement with SHA512.

[Gallaecio]

This is not a cryptographic use of md5, I believe, we are not handling unsafe input here, so I do not see the point: a slower algorithm with no added security benefit.

[florin-szilagyi]

@Gallaecio we should allow some sort of switch
md5 is not FIPS compliant, and will crash on FIPS enabled machines. unless the usedforsecurity=false which is only avaialable on python >3.9

[Gallaecio]

Sounds like setting usedforsecurity=False on Python 3.9+ is the way forward, then.