[cap-talk] Covert channels

[David Barbour]

On Sun, Feb 20, 2011 at 6:46 PM, David Wagner <daw at cs.berkeley.edu> wrote:
> Tim Freeman  wrote:
>> A lot of covert channels seem to concern time, so if you're trying to
>> block them then access to the computer's current time of day should be
>> considered security-sensitive.
>
> I would classify that approach under the category of 'crippling
> the functionality or usefulness of your computer system'.

It wouldn't be a problem if you allowed access to logical time.

I do limit access to even logical time through a capability - albeit,
an unum, which means even untrusted web-app code has access to it. The
reason is more for easy unit-testing than security.

>
> [Time] is used pervasively in network protocols (TCP has timeouts
> all over the place).

If you ever give untrusted code direct access to network protocols,
you clearly aren't worried about covert channels.

Dave