On Thu, Aug 08, 2002 at 09:15:33PM -0700, Seth David Schoen wrote:
> Back in the Clipper days [...] "how do we know that this
> tamper-resistant chip produced by Mykotronix even implements the
> Clipper spec correctly?".
The picture is related but has some extra wrinkles with the
TCPA/Palladium attestable donglization of CPUs.
- It is always the case that targetted people can have hardware
attacks perpetrated against them. (Keyboard sniffers placed during
court authorised break-in as FBI has used in mob case of PGP using
Mafiosa [1]).
- In the clipper case people didn't need to worry much if the clipper
chip had malicious deviations from spec, because Clipper had an openly
stated explicit purpose to implement a government backdoor -- there's
no need for NSA to backdoor the explicit backdoor.
But in the TCPA/Palladium case however the hardware tampering risk you
identify is as you say relevant:
- It's difficult for the user to verify hardware.
- Also: it wouldn't be that hard to manufacture plausibly deniable
implementation "mistakes" that could equate to a backdoor -- eg the
random number generators used to generate the TPM/SCP private device
keys.
However, beyond that there is an even softer target for would-be
backdoorers:
- the TCPA/Palladium's hardware manufacturers endoresment CA keys.
these are the keys to the virtual kingdom formed -- the virtual
kingdom by the closed space within which attested applications and
software agents run.
So specifically let's look at the questions arising:
1. What could a hostile entity(*) do with a copy of a selection of
hardware manufacturer endorsement CA private keys?
( (*) where the hostile entity candidates would be for example be
secret service agencies, law enforcement or "homeland security"
agencies in western countries, RIAA/MPAA in pursuit of their quest to
exercise their desire to jam and DoS peer-to-peer file sharing
networks, the Chinese government, Taiwanese government (they may lots
of equipment right) and so on).
a. Who needs to worry -- who will be targetted?
Who needs to worry about this depends on how overt third-party
ownership of these keys is, and hence the pool of people who would
likely be targetted.
If it's very covert, it would only be used plausibly deniably and only
for Nat Sec / Homeland Security purposes. It if becomse overt over
time -- a publicly acknowledged, but supposedly court controlled
affair like Clipper, or even more widely desired by a wide-range of
entities for example: keys made available to RIAA / MPAA so they can
do the hacking they have been pushing for -- well then we all need to
worry.
To analyse the answer to question 1, we first need to think about
question 2:
2. What kinds of TCPA/Palladium integrity depending "trusted"
applications are likely to be built?
Given the powerful (though balance of control changing) new remotely
attestable security features provided by TCPA/Palladium, all kinds of
remote services become possible, for example (though all to the extent
of hardware tamper-resistance and belief that your attacker doesn't
have access to a hardware endorsement CA private key):
- general Application Service Providers (ASPs) that you don't have to
trust to read your data
- less traceable peer-to-peer applications
- DRM applications that make a general purpose computer secure against
BORA (Break Once Run Anywhere), though of course not secure against
ROCA (Rip Once Copy Everywhere) -- which will surely continue to
happen with ripping shifting to hardware hackers.
- general purpose unreadable sandboxes to run general purpose
CPU-for-rent computing farms for hire, where the sender knows you
can't read his code, you can't read his input data, or his output
data, or tamper with the computation.
- file-sharing while robustly hiding knowledge and traceability of
content even to the node serving it -- previously research question,
now easy coding problem with efficient
- anonymous remailers where you have more assurance that a given node
is not logging and analysing the traffic being mixed by it
But of course all of these distributed applications, positive and
negative (depending on your view point), are limited in their
assurance of their non-cryptographically assured aspects:
- to the tamper resistance of the device
- to the extent of the users confidence that an entity hostile to them
doesn't have the endorsement CA's private key for the respective
remote servers implementing the network application they are relying
on
and a follow-on question to question 2:
3. Will any software companies still aim for cryptographic assurance?
(cryptographic assurance means you don't need to trust someone not to
reverse engineer the application -- ie you can't read the data because
it is encrypted with a key derived from a password that is only stored
in the users head).
The extended platform allows you to build new classes of applications
which aren't currently buildable to cryptographic levels of assurance.
eg. It allows general purpose policies to be built just by writing
policy code that sits in a Trusted Agent code compartment, without
having to figure out how to do split-trust (a la mixmaster chaining),
or forward-secrecy or secret-sharing or any of the other funky stuff;
you can just implement some policy code and it becomes so.
The danger is people will use it to build applications with squishy
interiors, with no cryptographic assurance. Forward-secrecy
implemented only by a policy in a Trusted Agent that sets a time-limit
on access. Anonymity but only in the sense that you trust the
hardware isn't tampered with, etc etc.
It will be really tempting because:
- it's much easier: network distributed crypto protocols are
relatively complex
- you can build things you can't otherwise build, the are currently
unsolved problems with distributed crypto protocols
- even where good crypto protocols exist, people will defend not using
them by claims to paranoia: "What you think the NSA has tampered with
your CPU?", or just laziness, cost of implementation etc
So in short probably mostly the answer will be "No", people won't
still aim for cryptographic assurance.
And so a big networked world of distributed applications with a very
squishy and insecure interior inside the closed world will be built.
The new application spaces squishy interior -- like a corporate
firewall with poor to no internal security -- could be ok if you could
be sure the firewall is 100% guaranteed reliable. TCPA/Palladium
proponents are effectively claiming it be an air-gap grade firewall
guarding the distributed closed world application spaces squishy
interior. But there is a problem: there are master keys by-passing
all that -- the endorsement CA's private keys.
4. What coming political battles will result?
a. If TCPA/Palladium systems get built -- and it may be politically
unstoppable given the power of the distributed security paradigm it
opens up -- then the battle of the coming decades will center around
control of access to that squishy interior. The keys that control
access to the closed world are the endoresment CA private keys.
b. You will see many clipper like attempts by governments attempting
to make policies surrounding conditional access to that closed world:
- law enforcement access to the endorsement private CA keys
controlling access, so they can setup sting operations,
demand that ISPs and ASPs collaborate with virtualized versions
of network services so they can trace things
- NSA designed protocols to allow such things, black box mediated,
court order approved, split database access to hardware
manufacturers private keys
c. As b. progresses RIAA/MPAA will chime in protesting that:
- Kazaa2 is distributing 10 exabytes a day of ripped recent release
content not based on BORA (which is now somewhat harder), but on
ROCA (Rip Once Copy Anywhere) as the content rippers move into
hardware hacking territory
- the RIAA/MPAA can't hack, spoof or jam kazaa2 with bogus content
because cypherpunks have fixed the protocols using WoT, certified
content, and other crypto-fu so they can't even observe who's
downloading what or who's serving what
- and therefore they also demand access to the closed world so they
can exert their recent legal rights to hack and DDoS the file
sharing networks
d. Unauthorised access to the closed environment (by hacking your own
hardware) will become illegal with DMCA like restrictions (if it
wouldn't already be where some relation to copyright could be drawn).
e. Software companies, and OS vendors will follow Microsoft's current
lead into an unholy battle with highlights such as:
- undocumented APIs to gain advantage over competitors, not only
hardware hacking required to discover APIs, but attestation to
ensure only those companies who have licensed the right to use
the API can use it
- incompatible file formats to lock out competition with
hardware tamper resistance levels of assurance, even file formats
that must have certified documents for applications to open them,
so even if you had the spec you couldn't be compatible
- copyright protection with software encrypted for the CPU, so you
can't even audit the static code
- software renting models again enforced by hardware
- whole collection of 2nd generation IP "innovations" which will be
built on top of such things
- charge per person you share file in a given document format;
- charge per format conversion
f. Lucky's Documentat Revocation lists to allow governments, companies
etc to to some extent after the fact control distribution of data
g. Increasingly minute enforcement of repressive levels of IP
tracking, and arbitrarily user hostile, fair-use eroding document
viewing and use policies
5. What could be done to protect the user?
a. implement cryptographic assurance inside the closed space where
possible -- that way if you are targetted by someone able to get
inside it you still have the same protection as now.
b. use web-of-trust techniques to provide an overlay of trust on the
endorsement trust. ie users endorse their own machines to say "this
is my machine" this implies that either:
- it's not tampered with (presuming the user himself was not a target
of some attack or investigation)
- or the only tamperer is the certifying user
web-of-trust overlaid on the hardware endorsement helps as:
- This makes the endorsement keys less useful in a
covertly obtained endorsement CA private key scenario
- Even if there are court authorized law enforcement access to
endorsement CA private keys, or RIAA/MPAA access to endorsement CA
private keys you can to the extent of your connectivity in the web
of trust, better avoid using the services of rogue
agents inside the closed space.
c. Demand ability to audit information in-flows into trusted agents
where there are unauditable out-flows; demand that this is implemented
in a way which allows code under user control to audit
d. Demand the ability to audit information out-flows, where there are
unauditable in-flows or sensitive user data processed by the
application; similarly demand that this is implemented in a way which
allows code under user control to audit
e. Demand cryptographically assured anonymity protection so that there
are no "trusted third parties" who can link your network usage and
identify you.
e. Other ideas? (Other than to lobby to prevent the building or use
this model).
Adam
--
http://www.cypherspace.org/adam/
[1] "FBI Bugs Keyboard of PGP-Using Alleged Mafioso", 6 Dec 2000,
slashdot
http://slashdot.org/yro/00/12/06/0255234.shtml
