Ok, I've made a little proof-of-concept system that seems to be working, but I'm wondering how effective it will be over the long run. I've made a bootable CD-ROM with an initrd losetup-like bootstrap. The only unencrypted data will be on the boot floppy/cdrom which can be removed after bootup. That leaves me with about 8GB of serpent-encrypted filesystems on the harddrive. This has some different issues than I normally think about. The box is designed to be shut-down-secure (to the point of using an ext3 journalled filesystem for abrupt powerdowns), which is fine since getting caught with the filesystems mounted makes the encryption issues moot. In theory, you could send me something like known-plaintext-email or something, but then you would still need before-and-after access to my harddrive to compare. If anything, I'm wondering about its security in the face of someone having possession of the computer and trying to decrypt it. Right now, worst offense, I have a 1K bit of (fixed) random garbage on the front of my filesystem that I use to identify my filesystems before I try to mount them. Right now, that is a kludge (mostly because I didn't feel like trying to validate the superblock and I thought I might have to store some information). There are all kinds of ways I could take the curse off of it, but just how bad is that? Once you get past that, look at the filesystem superblocks. You get a lot more variables in it which would make it harder to bruteforce, but a *lot* of them are based on filesystem size and be a lot more predictable that you might think. How secure is that, really? At what point is someone going to get burned? I started out looking into it as a security and anti-tampering system -- even if someone did have physical possession or access to the hardware, it wouldn't do them a lot of good without a LOT (hopefully horribly prohibitive) of work. How many bits do I have to give them before my effort is all for naught? Linux-crypto: cryptography in and on the Linux system Archive: http://mail.nl.linux.org/linux-crypto/
