Apr 29, 2011

BIOS Password Backdoors in Laptops

When a laptop is locked with password, a checksum of that password is stored to a sector of the FlashROM - this is a chip on the mainboard of the device which also contains the BIOS and other settings, e.g. memory timings. For most brands, this checksum is displayed after entering an invalid password for the third time:

The dramatic 'System Disabled' message is just scare tactics: when you remove all power from the laptop and reboot it, there are not new penalties such as additional passwords, locks and so on. From such a checksum (also called "hash"), valid passwords can be found by means of brute-forcing. Another method commonly used is that instead of a checksum, a number is displayed from which a randomly generated password can be calculated. Quite often, vendors also resort to storing the password in plain text, and instead of printing out just a checksum, an encrypted version of the password is shown. Either way, my scripts can be used to derive valid passwords with the hash.

Some vendors have implemented obfuscation measures to hide the hash from the end user - for instance, some FSI laptops require you to enter three special passwords for the hash to show up (see other post). HP/Compaq laptops only show the hash if the F2 or F12 key has been pressed prior to entering an invalid password for the last time.

Depending on the "format" of the number code/hash (e.g. whether only numbers or both numbers and letters are used, whether it contains dashes, etc.), you need to choose the right script - it is mostly just a matter of trying all of them and finding the one that matches your laptop. It does not matter on what machine the script are executed, i.e. there is no reason to run them on the locked laptop.
This is an overview of the algorithms that I looked at so far:
Vendor Hash Encoding Example of Hash Code/Serial Scripts
Compaq 5 decimal digits 12345 pwgen-5dec.py
Windows binary
Dell serial number 1234567-595B

Windows binary&source
Fujitsu-Siemens 5 decimal digits 12345 pwgen-5dec.py
Windows binary
Fujitsu-Siemens 8 hexadecimal digits DEADBEEF pwgen-fsi-hex.py
Windows binary
Fujitsu-Siemens 5x4 hexadecimal digits AAAA-BBBB-CCCC-DEAD-BEEF pwgen-fsi-hex.py
Windows binary
Fujitsu-Siemens 5x4 decimal digits 1234-4321-1234-4321-1234 pwgen-fsi-5x4dec.py
Windows binary
Hewlett-Packard 5 decimal digits 12345 pwgen-5dec.py
Windows binary
Hewlett-Packard/Compaq Netbooks 10 characters CNU1234ABC pwgen-hpmini.py
Windows binary
Insyde H20 (generic) 8 decimal digits 03133610 pwgen-insyde.py
Windows binary
Phoenix (generic) 5 decimal digits 12345 pwgen-5dec.py
Windows binary
Samsung 12 hexadecimal digits 07088120410C0000 pwgen-samsung.py
Windows binary

The .NET runtime libraries are required for running the Windows binary files (extension .exe). If the binary files (.exe) don't work out for you, install Python 2.6 (not 3.0!) and run the .py script directly by double-clicking them. Make sure that you correctly read each letter (e.g. number '1' vs letter 'l').
Source: http://dogber1.blogspot.com/2009/05/table-of-reverse-engineered-bios.html

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