Messages in this thread | | | Date | Tue, 5 Apr 2005 14:43:30 +0100 | From | Felipe Alfaro Solana <> | Subject | Re: crypting filesystems |
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On Apr 4, 2005 9:51 PM, Wiktor <victorjan@poczta.onet.pl> wrote: > Hi, > > I'm using the following method and it seems to be working fine > (involving crypto-loop): > > i have normal ext3 /boot partition, where i store kernel image & initrd. > after lilo boots the kernel, initrd sets up /dev/loop0 to be > crypto-loop/blowfish for /dev/hda1 (losetup /dev/loop0 /dev/hda1 -e > blowfish). losetup asks for passphrase, and (if entered correctly), > /dev/loop0 is mounted as root filesystem (it can be done also by simple > mount call: mount /dev/hda1 /some-place -o rw,encryption=blowfish). for > encrypting more filesystems with one passphrase, you can read it in > shell script in non-echo-mode (if such exists, i'm not sure), and pass > it to mount or losetup. crypto-loop makes possible to switch encryption > type without modifying whole initrd. > > Regarding your questions: > > > 1. In order to put in the passphrase just once a time at booting, I > put the passphrase in a gpg-crypted file (cipher AES256 and 256Bit key > size), which is decrypted at boot-time to /tmp (-> tmpfs) and > immediately removed with shred, after activating the three partitions. > Is it possible to see the cleartext password after this action in tmpfs? > > Disk encryption usually protects from hardware-attacks (when hacker has > physical access to the hardware). if you keep passphrase > reversible-encrypted, attacker can read it and run brute-force attack > using some huge-computing-capacity. is this what you want? > > > 2. Is it possible to gain the passphrase from the active encrypted > partitions (because the passphrase is somewhere held in the RAM)? > > Only when attacker has root privileges. But i'm not sure if it is > possible to extract passphrase knowing both encrypted and not encrypted > data. What i mean is that usually each filesystem begins with > filesystem-specyfic-header, which is constant or similar to each other. > so, if attacker has encrypted form of this header and can estimate > unencryptes form, it can possibly gain the passphrase. (but therse are > only my ideas, i don't know how the encryptino-algorithm works).
What´s kept in RAM is the AES key used to decrypt disk blocks. However, the passphrase from which the AES key is derived (usually by using a hash function) is not kept in memory. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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