The Anthropic Side Channel (was: How would shallow generators compose with lambda?)

Brendan Eich brendan at
Fri May 15 14:26:49 PDT 2009

On May 14, 2009, at 5:42 PM, Mark S. Miller wrote:

> On Thu, May 14, 2009 at 3:42 PM, Brendan Eich <brendan at>  
> wrote:
>> On May 14, 2009, at 2:50 PM, Mark S. Miller wrote:
>>>> If so, did you have a different way of reasoning about the  
>>>> reasons today
>>>> why
>>>> finally might not run that I mentioned (iloop detection or other  
>>>> hard
>>>> stop)?
>>> Those hard stops kill all further activity within that event loop.
>>> Once a universe has been destroyed, no further bad things can happen
>>> in that universe.
>> There's always the next universe (new event starts another control  
>> flow).
>> Life goes on, in the JS serial multiverse, and those finally  
>> clauses failed
>> to run even though control abruptly left the lambda under the  
>> hypothesis.
> I am assuming that a hard stop destroying an event loop also destroys
> (at least makes inaccessible) all objects that were able to execute
> within that event loop.

You're right that this is necessary with threads and fail-stop  
information flow systems, but plain old iloop DOS prevention as  
practiced in browsers does *not* reload the page. And the browser APIs  
are full of  ways to detect that finallys didn't run, through effects  
overt and covert.

>> This isn't entirely academic, since information leaks include  
>> termination
>> channels.
> I do not expect to be able to plug such information leakage channels,
> and was not trying to. But again, this doesn't endanger any object
> invariants.

Just consider iloop DOS prevention as practiced in browsers today:  
finally may not run. That's enough.

> A similar, but (to me at least) more surprising information leakage
> channel is something I've called "The Anthropic Side Channel":

[fun example snipped]

> So, the anthropic side channel enables B to communicate what Brendan
> might call a half a bit of information to C.

You must be referring to my slides at 
  -- I should have better slides blogged next week.


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