I just discovered cryptsetup-reencrypt. It's experimental and slow, but it's a wonderful tool I'm very happy to have in Jessie. :D
One possible usage is with --use-random after the installation is complete (see #723729). Unfortunately, it can only work on unmounted partitions. So I believe it would be a nice addition to the rescue disk, if we can spare 45kB. -- Nirgal
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