Re: Can a program prove it's own integrity?

From: Kiuhnm (invalid_at_invali.it)
Date: 05/19/04 

Date: Wed, 19 May 2004 00:54:27 GMT

AE wrote:
> This is where the idea comes from:
>
> I wanted to protect a complete harddisk - encrypting disk driver,
> modified bootloader to run the operating system from the encrypted
> disk.
>
> The weak point is the bootloader: If it is changed an attacker can
> read the password as I'm typing it and all security is gone.

Write a self-decrypting pre-bootloader that, in order to work properly and
eventually decrypt the real bootloader on the hard disk, needs some random
data.
Put the pre-bootloader and the random (or compressed cryptographic) data on
a floppy disk. Your floppy disk must be *full* and the data nearly
incompressible (just use a state-of-the-art compressor).
The encrypted part of the pre-bootloader, once decrypted and executed, must
enter the highest privilege level (e.g. Ring 0), use time-stamp instructions
and execute *many* difficult-to-emulate operation (the code could test the
"protected mode" functionalities..., execute pmode BIOS extension, etc...).
The code will also check the floppy disk hash and print "expected secret
strings" on the screen.

You could use a low-density floppy disk (it's more efficient because you
have less data).

You should:
1) (physically) disconnect the hard disk,
2) (physically) write-protect the floppy and insert it,
3) turn on your computer,
4) insert the password,
5) wait :-)
6) Examine the screen and decide if the floppy disk is genuine.
If you think it's genuine:
7) turn off your computer,
8) reconnect the hard disk,
9) turn on your computer,
10) etc...

Notes:
- your hard disk must be disconnected or the attacker could copy partial
data of the floppy to the hard disk (even if it's encrypted);
- your pre-bootloader should even check hashes of your BIOS, etc...
- Once your software enters Ring 0, no one can completely control it. One
can only run that program in a virtual machine and still it's very difficult
to emulate perfectly all the functionalities and handle accurately all the
time-stamp instructions. Anyhow, a virtual machine requires a lot of code
and it's practically impossible to compress the data in the floppy in order
to create enough space for the virtual machine.
- When you find out that the floppy is compromised, your password could have
just been saved somewhere in the BIOS, etc...
This is not a problem: just create another disk and use another password.
Your true bootloader can't be revealed while you execute the pre-bootloader
with the hard disk disconnected.

Kiuhnm

Relevant Pages

  • Re: Can a program prove its own integrity?
    ... ]>>I wanted to protect a complete harddisk - encrypting disk driver, ... ]>>modified bootloader to run the operating system from the encrypted ... ]> eventually decrypt the real bootloader on the hard disk, ... Your floppy disk must be *full* and the data nearly ...
    (sci.crypt)
  • RE: floopy disk analyzer
    ... I understand you want to find a tool which can analyze floppy disk. ... It seems that Anadisk you mentioned is a program can exam and fix some ...
    (microsoft.public.windowsxp.general)
  • Re: Why is the Hard Drive called "C" by default?
    ... yes A and B were used for floppy drives. ... easy copying of one floppy disk to another, and they were starting to get ... The first Personal Computers had a single floppy drive ...
    (microsoft.public.windowsxp.hardware)
  • Re: Notepad file on floppy disk.
    ... How else can I express it that your floppy disk is ... The floppy makes noise even while functioning ... "Rahul Singh" wrote: ... Maybe the floppy disk is unreadable. ...
    (microsoft.public.windowsxp.general)
  • Re: installing xp on a sata drive
    ... If he's gotten to the point of formatting the drive and copying files it's not too likely that it's a driver problem, it's more likely either he has a bad CD drive, bad CD, or a problem with the RAM or hard disk itself, those are the common causes of file copy errors during setup. ... Is there an entry for RAID/NoRAID in the BIOS? ... take out the floppy disk. ...
    (microsoft.public.windowsxp.setup_deployment)