Some prior art mentioned in public discussions: Glenn Everhart, 1978 (``I wrote an encrypting virtual disk driver for RSX11D back in 1978. It was published, with sources and docs on the Fall 1979 RSX SIG tapes. ... I did another for VMS in the late 80s sometime also given out freely.''); Matt Blaze, ``A cryptographic file system for UNIX,'' 1993; Matt Blaze, ``Key management in an encrypted file system,'' 1994.