Well, you missed checking what "cold boot" means, for example. Quoting from Wikipedia: "A hard reboot (also known as a cold reboot, cold boot or cold start) is when power to a computer is cycled (turned off and then on) or a special reset signal to the processor is triggered (from a front panel switch of some sort). This restarts the computer without first performing any shut-down procedure." The last sentence is what's important here. Kind regards, Anders On Sun, Jan 4, 2009 at 8:08 PM, Nicholas <nicholas@xxxxxx> wrote: > Regarding the Cold Boot attack, it occurred to me that all you would have > to do to defeat it is rig the linux kernel (or whatever OS you're using) > to just fill the memory with 0's before shutting down completely (assuming > a soft shutdown is possible). I'm not a computer programmer, but I would > imagine this would solve any problems with keys remaining in memory. Is > this a viable option? Or perhaps I'm missing something? > > --Nicholas > > On Fri, January 2, 2009 9:00 pm, markus reichelt wrote: >> Hi, >> >> since Jacob talked about his cold-boot attack stunt at 25C3[1,2] (go >> watch his talk, he mentions us but not the super-shy dm-crypt people >> :-) and I am still in the process of hacking some loop-AES magic into >> the recent Slackware (namely its installer), I wrote a script >> regarding the attack and attached it (let's hope the mailinglist >> software can cope - else you can get it from [3]) >> >> >> From the upcoming text: >> >> >> FAQ 28: Is there a defense against the cold-boot attack? >> >> In short, there is not. The only way to be safe is to prevent >> physical access to the machine in question. >> >> On the other hand, the attack aims towards aquiring encryption keys. >> So why not give the attacker both what he is looking for anyway and >> slow him down at the same time? Concerning loop-AES, follow these >> guidelines: >> >> - Disable network,USB,CD-ROM booting in BIOS and boot from harddisk >> (with the key residing on an external medium) >> >> - Use a different cipher than AES, namely Serpent. >> >> - If you must use the AES cipher, do not use key scrubbing. >> >> - And most importantly, set up as many encrypted loop-devices as >> possible. >> >> The attacker does not know about the layout of your system, he is >> just looking for encryption keys within a memory image he has >> obtained through questionable methods. So by spamming the system RAM >> with encryption keys you let the attacker sort it all out and do not >> make it deliberatly easy for him by just setting up the few encrypted >> loop devices you actually use. Trade memory for time. >> >> While this procedure does not stop the attacker, it surely slows him >> down. Maybe this attack is carried out with a relatively short >> time-window and this procedure just might buy you the time (or >> obscurity) you need - who knows? >> >> In case you know or have a feeling that your system has been >> subjected to the cold-boot attack (f.e. at US customs, a friendly >> visit of your DHS agent, ...), ditch your current crypto setup and >> recreate it from scratch. >> >> >> You can use this script to set up a number of encrypted loop-devices >> automatically on boot, different available ciphers are chosen >> somewhat randomly. Feel free to adapt it to your needs. >> >> first adapt the config. then f.e. use >> >> loopsetup.sh 33 setup >> >> in order to set up encrypted loop-devices 33-254 with >> aes256,serpent256,twofish256 picked somewhat-randomly >> >> and if you want to detach encrypted loop-devices again use >> >> loopsetup.sh 33 destroy >> >> >> >> [1] http://events.ccc.de/congress/2008/Fahrplan/events/2922.en.html >> [2] >> http://ftp.ccc.de/congress/25c3/video_h264_720x576/25c3-2922-en-advanced_memory_forensics_the_cold_boot_attacks.mp4 >> [3] http://mareichelt.de/pub/mine/loopsetup.sh >> -- >> left blank, right bald >> loop-AES FAQ: http://mareichelt.de/pub/texts.loop-aes.php#faq > > > > - > Linux-crypto: cryptography in and on the Linux system > Archive: http://mail.nl.linux.org/linux-crypto/ > > - Linux-crypto: cryptography in and on the Linux system Archive: http://mail.nl.linux.org/linux-crypto/
