Re: [Caml-list] Constant-time function

[Gerd Stolpmann <info@gerd-stolpmann.de>]

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Am Montag, den 22.02.2016, 15:16 -0500 schrieb Chan Ngo:
> Hi Milan,
> 
> 
> thanks, I see what you mentioned with the “&&” operator. In fact, one
> case the behavior as I wanted is in crypto primitive (we need
> constant-time function to avoid time side-channel attack, for example,
> give any input for comparing with the secret hash value with fixed
> size, the time execution of comparing is constant.

You can define an operator that behaves like this:

let ( &&& ) p q = p && q

There might be other functions whose run time varies with the input.
E.g. (string) equality comes to my mind.

Gerd

> 
> Best,
> Chan
> 
> > On Feb 22, 2016, at 3:12 PM, Milan Stanojević <milanst@gmail.com>
> > wrote:
> > 
> > Compiler short circuits && operator so your loop runs only til the
> > first element that differs. If you swap the arguments to && you
> > should get the behavior of visiting all elements (which is of course
> > undesirable in practice)
> > 
> > 
> > 
> 
> 

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Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
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