allow luks encrypted casper-rw persistent file (patch)

[Glenn Washburn]

Currently the casper-rw persistent file can not be an encrypted container. The distribution livecd would be a more valuable product, if it allowed persistence to an encrypted container. The persistence feature of the livecd is very likely to be used on removable media, such as a usb flash drive. These are generally small and thus easily lost or misplaced. This could prove to be a security issue if it contains sensitive data.

I've attached a patch which allows casper to detect when the casper-rw file is a luks encrypted container. It will then ask the user for the password, unlock the container, and use the unencrypted device as if it were an unencrypted casper-rw. This is a basic, self-contained solution to this issue.

A better solution would be to re-use the "setup_mapping" function in /scripts/local-top/cryptroot from initramfstools to setup the crypto device. However, it is currently not possible to source this function from another script because cryptroot calls "exit".

What this patch does not support:
* using a keyfile to decrypt the luks device
* support for persistent, encrypted device partitions (must use an encrypted file on a supported filesystem)
* support for other encrypted container formats (true-crypt, loop-aes, etc..)

Reference:
* http://ubuntuforums.org/showthread.php?t=1044182
* http://ubuntuforums.org/showthread.php?t=1171612

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "luks-persistent-img.ubuntu.patch" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

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[Ed N. (ed056)]

This would be a very useful feature. I avoid using persistence due to security concerns if the usb is lost and things line my Ubuntu One login were on it. (which has happened to me.) The fix looks trivial to me and I'm sure it would get a lot of usage if available and known.

This article covers the change needed.
https://archimedesden.wordpress.com/2013/09/12/encrypted-persistent-storage-on-ubuntu-livecd/

[Glenn Washburn (crass)]

An updated post of what needs to be done for yakkety (16.10) is at:
https://archimedesden.wordpress.com/2017/01/09/encrypted-persistent-ubuntu-livecd-16-10-redux/

It seems trivial to have this included in the iso. Most of the work of figuring out what changes to make have been done, so what's the down-side? It looks like recent isos do not include dm-crypt nor cryptsetup as the blog post alludes to. So they need to be added back, but its not that much extra data.