[Distutils] Proposal: drop md5 for sha256

[Tarek Ziadé]

On 7/4/12 2:50 AM, PJ Eby wrote:
> On Tue, Jul 3, 2012 at 7:33 PM, Jennings, Jared L CTR USAF AFMC 46 
> SK/CCI <jared.jennings.ctr at eglin.af.mil 
> <mailto:jared.jennings.ctr at eglin.af.mil>> wrote:
>
>     On hosts configured for compliance with U.S. Federal Information
>     Processing Standard (FIPS) 140-2
>     <http://csrc.nist.gov/publications/fips/fips140-2/fips1402.pdf>, like
>     those in some banks and, yes, the U.S. Department of Defense,
>     cryptographic modules (such as OpenSSL, which underlies hashlib)
>     are not
>     allowed to calculate MD5 digests, because MD5 is no longer a FIPS
>     Approved digest algorithm.
>
>
> So if it's not a cryptographic module, it's okay?  ;-)
>
>     I know no one is trying here to lean on MD5 for security, but the
>     standard says nothing about the reason why you're using MD5: just that
>     you can't.
>
>     No one expects a digest algorithm to fail, and Python 2.x may not have
>     been fixed to check for that before being frozen
>     <https://bugzilla.redhat.com/show_bug.cgi?id=746118#c3>, so if you run
>     an MD5 checksum on a FIPS-compliant system with an unpatched
>     Python 2.x,
>     the Python interpreter will segfault. (Ruby, too, had this problem and
>     was itself only recently fixed,
>     <http://bugs.ruby-lang.org/issues/4944>.)
>
>     I have to configure hosts in accordance with FIPS 140-2, so the more
>     places I can get rid of MD5, the less headaches I have.
>
>
> If we replace it with something else, then I suggest we replace it 
> with something that's even MORE braindead than md5 so that nobody will 
> mistake it for a secure hash.  Otherwise, we will have this exact same 
> problem all over again when the replacement "secure" hash is disabled 
> by a newer version of FIPS.
>
> The other option is simply to forego a checksum altogether and assume 
> same size = same file.  Honestly, I don't remember why we cared about 
> detecting such modifications in the first place: neither PEP 376 nor 
> 262 explain why, and 376 doesn't explain why it went with md5 instead 
> of sha1 (as in PEP 262).

I wanted to be able to offer a way for installers to detect that a file 
was changed to avoid deleting it for instance, and issue a warning to 
the user -- or maybe give a chance to the installer to save a copy of 
the file somewhere.

I picked md5 because I wanted it brain dead and could not imagine that 
would  be an issue somehow. Maybe zlib.crc32 would be a better choice.

If we remove the hash, oh well. no big deal I guess. If an installer 
wants to add this feature it can maintain hashes itself.


>
>
>
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