pymatgen/io/vasp/inputs.py md5 call gets an error when FIPS is enabled

[bernstei]

Describe the bug
pymatgen/io/vasp/inputs.py calls hashlib.md5 for hashing in a way that generates an error on RedHat systems that have FIPS enabled.

To Reproduce

On a RedHat machine that has FIPS enabled, do any pymatgen operation that reads a potcar, e.g. Potcar.from_file("POTCAR"))

The resulting output is

  File "/home/Software/python/system/extra/lib64/python3.9/site-packages/pymatgen/io/vasp/outputs.py", line 401, in __init__
    self.update_potcar_spec(parse_potcar_file)
  File "/home/Software/python/system/extra/lib64/python3.9/site-packages/pymatgen/io/vasp/outputs.py", line 1148, in update_potcar_spec
    potcar = self.get_potcars(path)
  File "/home/Software/python/system/extra/lib64/python3.9/site-packages/pymatgen/io/vasp/outputs.py", line 1118, in get_potcars
    potcar = get_potcar_in_path(os.path.split(self.filename)[0])
  File "/home/Software/python/system/extra/lib64/python3.9/site-packages/pymatgen/io/vasp/outputs.py", line 1103, in get_potcar_in_path
    pc = Potcar.from_file(os.path.join(p, fn))
  File "/home/Software/python/system/extra/lib64/python3.9/site-packages/pymatgen/io/vasp/inputs.py", line 2240, in from_file
    single = PotcarSingle(p)
  File "/home/Software/python/system/extra/lib64/python3.9/site-packages/pymatgen/io/vasp/inputs.py", line 1811, in __init__
    self.hash = self.get_potcar_hash()
  File "/home/Software/python/system/extra/lib64/python3.9/site-packages/pymatgen/io/vasp/inputs.py", line 2151, in get_potcar_hash
    return md5(hash_str.lower().encode("utf-8")).hexdigest()
ValueError: [digital envelope routines: EVP_DigestInit_ex] disabled for FIPS

Expected behavior
successful parsing of the POTCAR file

Environment (please supply relevant versions and platform info):

Rocky Linux 8 with FIPS enabled

Additional context

This discussion s3tools/s3cmd#1005 strongly indicates adding the usedforsecurity=False to the md5() call will avoid the error, which is caused because md5 is not a secure hash for security purposes. I'm currently checking this locally and will post a followup when I see if it works.

[bernstei]

Adding usedforsecurity=False to the hashlib.md5 calls in pymatgen/io/vasp/inputs.py fixes the issue for us. I suspect the same argument should also be added to the calls in pymatgen/io/abinit/pseudos.py as well, but I didn't see any other relevant calls.