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On Fri, Jun 15, 2012 at 9:41 AM, Nick Coghlan <report@bugs.python.org>wrote:
>
> Nick Coghlan <ncoghlan@gmail.com> added the comment:
>
> To repeat, the specific feature being proposed for retention is:
>
> * a function called hmac.total_compare() that is clearly documented as
> being still vulnerable to timing analysis given a sufficiently
> sophisticated attacker, while still being more resistant to such analysis
> than the standard comparison operator
>
> * restricting that function to operating on bytes, to eliminate timing
> variations associated with encoding/decoding of Unicode text and reduce
> those associated with the calculation of integer values
>
> Leaking less information on each comparison is intended to increase the
> effectiveness of higher level timing attack countermeasures (such as rate
> limiting and lockouts). Anyone that would use "hmac.total_compare" and call
> it done is likely using ordinary comparison today (which is even worse).
>
> ----------
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue15061>
> _______________________________________
>
Nick, I fail to understand why are you opposing writing such a function in
C. Such a function can be provably time-independent (and as MvL says this
is a binary state), at least as long as it operates on bytes (I'll refrain
from asking about unicode, I think it's possible, but I dunno).
For the same function in python it's at the very least much harder to prove
(and has bugs as we've seen)
Cheers,
fijal