BIOS Password Backdoors in Laptop

 

Synopsis: The mechanics of BIOS password locks present in current generation laptops are briefly outlined. Trivial mechanisms have been put in place by most vendors to bypass such passwords, rendering the protection void. A set of master password generators and hands-on instructions are given to disable BIOS passwords.

When a laptop is locked with password, a checksum of that password is stored to a so-called FlashROM – this is a chip on the mainboard of the device which also contains the BIOS code 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, it will work just as before. From such a checksum (also called “hash”), valid passwords can be found by means of brute-forcing.

The bypass mechanisms of other vendors work by showing a number to the user from which a master password can be derived. This password is usually a sequence of numbers generated randomly.

Some vendors resort to storing the password in plain text onto the FlashROM, and instead of printing out just a checksum, an encrypted version of the password is shown.

Other vendors just derive the master password from the serial number. Either way, my scripts can be used to get valid passwords.

A few 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 (e.g. “3hqgo3 jqw534 0qww294e, “enable master password” shifted one up/left on the keyboard). Some 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 fits 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:

 

 

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