Onderwerp: Mobile Device Security, Was: Re: Dell BIOS DoS

Ross Draper(Ross.Draper@musicradio.com)@2003.12.09 20:08:31 +0000:
> I agree with your points Jon, but lets be fair here, BIOS passwords do
> have a use - especially on laptops.

They will prevent a certain subset of individuals from starting your
laptop.

x86 BIOSes nowadays are modularized and contain quite a lot of modules to
boot from PCMCIA/CardBus devices or even FireWire. They can netboot,
etc. What they apparently cannot do is check the presence of a USB
token and challenge it for a signature, but this would be an option to
get rid of vendor master passwords and such. Deliver two keys with the
box, store one in a safe location, that's it.

On PowerPC the systems are booted through OpenFirmware, which is even
more complex. On Apple machines the boot ROM contains a graphical
selector for boot devices which has mouse support. On a Mac you do
not have any password protection, although it would be possible to
implement. Apple try to solve the security situation with FileVault
(encrypting the contents of your home directory), but data is not stored
exclusively in the user's home directory.

The main question is: where is the real point of attack?
Answer: there's not just one threat, there are several.

Imagine someone stealing your laptop which is ssecured with some sort of
password. He rips apart the chassis, pulls out the harddrive and takes
the data he's after, no matter how your boot protection looked like.

The crypted harddrive issue is a different one. It also has a lot of
weaknesses, although it is probably more secure in terms of data theft
than any other method for securing mobile devices. The point here is,
that an attacker would break into the running system, thus circumventing
boot protection.

Even worse: what if the attacker stole your token to unlock the drive
crypto? You'd be having no useable laptop at all.

What's missing is true platform integration, which appears quite hard to
do. Boot ROM modifications, HD crypto, software crypto, screensaver
passwords are only one part of the story.

What I'd prefer for mobile use is a system comprised of hard-, firm- and
software that plays together, not side-by-side. Surely, this integration
might increase the attack surface, but it would be capable of delivering
the set of features needed on a mobile unit, protecting the "cold"
(switched-off) device as well as boot stage and running system.

Just a few way unsorted thoughts...

Regards,
/k

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> tried it. --Donald Knuth
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Not sure that the sentiments below are 100% correct - see Ross Andersons
papers on logical and API attacks upon tamper resistant hardware,
faciltated by physical (or near physical) access to the hardware.

If you can do it in software, you can break it in software.

Lyal

-----Original Message-----
From: Craig Paterson [mailto:craigp@tippett.com]
Sent: Wednesday, 10 December 2003 7:03 AM
To: David Brodbeck
Cc: 'jon schatz'; bugtraq@securityfocus.com
Subject: Re: Dell BIOS DoS


David Brodbeck wrote:

>There is no such thing as security from someone who has physical access
to
>the hardware.
>

Alright, so this is a tangent, but: that is what encryption is for. The
whole basis of encryption assumes that the attacker has access to the
message (your data), but that without the appropriate keys you can't
usefully access it. No, this doesn't have much to do with the value or
otherwise of BIOS passwords, but it's often stated that physical access
renders all your data wide open, which isn't necessarily the case.

Craig.

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On Dec 9, 2003, at 12:02 PM, Craig Paterson wrote:

> David Brodbeck wrote:
>
>> There is no such thing as security from someone who has physical
>> access to
>> the hardware.
>>
>
> Alright, so this is a tangent, but: that is what encryption is for.
> The whole basis of encryption assumes that the attacker has access to
> the message (your data), but that without the appropriate keys you
> can't usefully access it. No, this doesn't have much to do with the
> value or otherwise of BIOS passwords, but it's often stated that
> physical access renders all your data wide open, which isn't
> necessarily the case.

I'll continue the tangent: Encryption's great against an attacker who
has physical access to the device holding your data, as long as they
don't have physical access to the device holding your keys! We can
sort of separate hardware into:

Type 1. Storage/transit parts which only handle encrypted data and
never see the key.
Type 2. Use/processing parts which operate on the unencrypted data,
and thus need the key (or only deal with the plain text in the first
place.)

The maxim then becomes "There is no such as security from someone who
has physical access to the (type 2) hardware."

I would describe most of the "secure/trusted hardware" efforts that
I've seen (such as the system Alexandros Papadopoulos mentioned) as
trying to move as much of the system type 1 as possible, and make the
type 2 bits user-inaccessible. There are a few interesting things you
can do with data without decrypting it at all (a pure type 1
situation), but most applications require some type 2 bits. The trick
with a secure cryptographic coprocessor is that the exposed data bus
can be type 1, with the type 2 operations happening somewhere inside.
This would accomplish nothing against an attacker with absolute
physical access who could read or change the voltage anywhere in the
chip at any time. But it does work against an attacker with "normal"
physical access who can only observe or tamper with data on the chip's
external interfaces.


--
Eric Anderson - anderson@cs.uoregon.edu
University of Oregon Network Security Research Lab
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On Tue, Dec 09, 2003 at 08:08:31PM -0000, Ross Draper wrote:
> I agree with your points Jon, but lets be fair here, BIOS passwords do
> have a use - especially on laptops.

An oft-overlooked use for BIOS passwords is an 'auditing' mechanism;
typically, when one resets a BIOS password via magic jumpers, removing
battery, etc, there is typically no way to put the password BACK.

So, someone who disables or destroys the BIOS password still stands a
good chance of being discovered, at the least.

--=20
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This way, when you get infected with a virus, my address won't appear in
the From: header. Thanks.

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>I'll continue the tangent: Encryption's great against an attacker who
>has physical access to the device holding your data, as long as they
>don't have physical access to the device holding your keys!

This is a bit different than your point, but one thing I've been trying to
find out, so far without any authoritative input, is how much of an
increased risk is it for a laptop that has a PGP disk on it to also have the
private key file accessible. Most installations default to the private (and
public) key rings being installed in the PGP program file directory.

For a while there, I always used removable media to store my key rings
(diskonkey, memory stick, etc.) as a "just in case" defense, but I've never
really had any confirmation that someone who has access to the encrypted
private key file (but not the passphrase) has a better chance of cracking
the encrypted data. In fact, the commercial version of PGP Corp's "Mobile
PGP for CE" does not have an option to change the location of the key
rings -- they stay on the handheld device itself, (as opposed to a secure
digital/compact flash card).

Is a weak passphrase more easily exploited with the presense of the key ring
vs direct attack against the encrypted data? Stuff like that...

Anyone have any insight?

T