The idea of a coldboot attack is to freeze the RAM while the operating system is still running (for example whilst you are on lunch break and your box is running but the screenlocker is enabled). This results in the RAM not loosing the data even if it looses power. An attacker can then reboot the device using his own operating system and extract any data from the RAM he desires.
Most interesting is usually the cryptographic key used to decrypt the harddrive. This can then be used by the attacker to decrypt your harddrive and access any data he likes.
For a successful attack, the attacker needs all of these to apply:
- The data he is after needs to be in your RAM
- He needs to be able to freeze your RAM
- He needs to be able to boot your computer into specially prepared system OR take out your RAM to access it in another system.
1.) Your operating system cannot access the data stored on your harddrive without the cryptographic key to decrypt it. This key needs to be stored in the RAM, you cannot avoid it. The only way to work around this is to shut down your computer whenever you leave.
2.) You can work around this by applying physical security measures such as tamper switches that wipe your RAM if the case is open. This might help against some attackers but a well prepared attacker that knows about the measures you applied will find a way to circumvent them.
3.) You could use a BIOS /UEFI that wipes your RAM as soon as your computer is turned on. An attacker would need to take out your RAM in order to read it out externally. Maybe you are able to apply physical protection against this, but a well prepared attacker will find a way to circumvent this, too.
In the end I think you should think about your threat model. Which attackers are actually relevant to you and your scenario? Is this actually the easiest way to get access to your data? Also remember the xkcd ;-)