[issue21306] PEP 466: backport hmac.compare_digest

[Donald Stufft]

Donald Stufft added the comment:

I'm not sure that the timing leakage in an encode is actually something to be worried about. I'm not sure what secret information would be getting leaked in a way that you could determine it by examining the timing.

However I think the bigger thing is if I'm an app developer and I attempt to pass a unicode to hmac.compare_digest() and it tells me it only accepts bytes, the first thing I'm going to do is is .encode() it myself before I pass it in.

IOW hmac.compare_digest could avoid the encode, but it's just pushing that back up to the user of hmac.compare_digest, who might possibly have a byte string laying around that they won't have to do the encode/decode dance on (although if they have a unicode they have already done it at least once), or they only have a unicode available to them then they'll be forced to do the encode themselves.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21306>
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