I have been working a lot on Elvis Pfützenreuter's pam_mount PAM module. This module allows one to mount, among other things, loopback encrypted filesystems at login time. The module makes it easy for a user to have an encrypted home directory. The module is available at http://www.flyn.org but is not quite ready for prime time. I recently added the concept of an encrypted filesystem key, similar to that which loop-AES uses. For example, given: sk system key, the key or password used to log into the system fsk filesystem key, the key that allows you to use the filesystem you wish pam_mount to mount for you E and D an openssl supported synchronous encryption/decryption algorithm efsk encrypted filesystem key, efsk = E_sk (fsk), stored somewhere on the local filesystem (ie: /home/user.key) Pam_mount will read efsk from the local filesystem, perform fsk = D_sk (efsk) and use fsk to mount the filesystem. If you change your system password, simply regenerate efsk using efsk = E_sk (fsk). Does this technique appear to make sense from a security point of view? I am using the following technique to create encrypted volumes with a random key, encrypted with the user's system password and stored on the local filesystem: a. dd if=/dev/urandom of=/home/user.img bs=1M count=<image size in MB> b. dd if=/dev/urandom bs=1c count=<keysize / 8> | openssl enc \ -<fs key cipher> > /home/user.key Encrypt this file using the user's login password as the key. c. openssl enc -d -<fs key cipher> -in /home/user.key | losetup -e aes \ -k <keysize> -p0 /dev/loop0 /home/user.img d. mkfs -t ext2 /dev/loop0 ... n - 1. umount /dev/loop0 n. losetup -d /dev/loop0 Again, does this technique also make sense? -- Mike :wq - Linux-crypto: cryptography in and on the Linux system Archive: http://mail.nl.linux.org/linux-crypto/
