Objection from hashlib maintainer: I will reject a used_for_security flag with default of False. I'm slowly moving Python to a secure-by-default policy. Therefore used_for_security must be an explicit opt-out.

I'm aware that the policy will require modifications to all software that uses MD5. To be honest that's my goal. If you care about FIPS, then any use of MD5 must be a concious and careful decision. I want developers to move away from MD5 and replace it with SipHash24, Blake2 or SHA-2. MD5 should *only* remain when backwards incompatibility prevent migration.