[issue15061] hmac.secure_compare() leaks information about length of strings

[Antoine Pitrou]

Antoine Pitrou <pitrou at free.fr> added the comment:

> > The point of supporting unicode would precisely be to avoid a
> > unicode->bytes conversion when unicode strings are received.
> 
> A byte-wise comparison of the memory representation would work IFF both
> sides have the same type and unicode kind. Anything else could give away
> details of the content.

My proposal was to only allow them on ASCII strings. Any other unicode
kind would raise an error (perhaps NotImplementedError).

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<http://bugs.python.org/issue15061>
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