Who cares about side-channel attacks?

[Peter Gutmann]

Ben Laurie <ben at links.org> writes:
>Peter Gutmann wrote:
>> Given the string of
>> attacks on crypto in embedded devices (XBox, iPhone, iOpener, Wii, some
>> not-yet-published ones on HDCP devices :-), etc) this is by far the most
>> at-risk category because there's a huge incentive to attack them, the result
>> affects tens/hundreds of millions of devices, and the attacks are immediately
>> and widely actively exploited (modchips/device unlocking/etc, an important
>> difference between this and academic proof-of-concept attacks), so this is the
>> one where I'd expect the vendors to care most.
>
>But they've all been unlocked using easier attacks, surely?

The published ones seem to be the (relatively) easy ones, but the ones that
have been tried (and either not published or just had the easy outcome
published) have been pretty amazing.  This is another one of these things
where real figures are going to be near-impossible to come by, even harder
than my hypothetical public vendor survey of who uses SCA protection.  You'd
have to read about 20 blogs and a hundred mailing lists, many private, just to
keep up, but from various informal contacts with people working in this area
it seems you're not looking at anything like the conventional "identify the
weakest point, then attack there" approach.  Instead what's being done is more
like the Iraqi weapons program prior to 1991 where they were using every
imaginable type of approach, including ones like calutrons that had been
abandoned decades earlier by everyone else, for a first-past-the-post finish,
they'd try anything and everything and whatever got them there first would be
declared the winner.  It's the same with these attacks, whenever I've asked
"have you tried X" the answer is invariably "yes, we have".

This style of attack is quite different from the usual academic model, it
neatly illustrates Bruce Schneier's comment that a defender has to defend
every single point along the line while an attacker only has to find a single
weakness.  In this case it seems to be literally true, and the weakness won't
necessarily be the actual weakest point but merely the point where an attacker
with sufficient skill and access to the right tools got in.  Look at the XBox
attacks for example, there's everything from security 101 lack of
checking/validation and 1980s MSDOS-era A20# issues through to Bunnie Huang's
FPGA-based homebrew logic analyser and use of timing attacks to recover device
keys (oh, and there's an example of a real-world side-channel attack for you),
there's no rhyme or reason to them, it's just "hammer away at everything with
anything you've got and exploit the first bit that fails".

Peter.

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