[LSF/MM TOPIC] ext4 Encryption Update: Policies, File Names, and Integrity

[Michael Halcrow <mhalcrow@google.com>]

I previously presented on ext4 encryption at the 2014 Linux Security
Summit:

http://kernsec.org/wiki/index.php/Linux_Security_Summit_2014/Abstracts/Halcrow

http://kernsec.org/files/lss2014/Halcrow_EXT4_Encryption.pdf

Our first prototype implementation has been in Ted Ts'o's unstable git
branch since November 2014. My team has made significant progress in
the months since, developing encryption policy and file name
encryption capabilities. We have completed the first major phase of
development and are preparing a patchset to iterate on the prototype.

I will present our approach at applying different encryption policies
to different segments of the file system via a policy inheritance
scheme. I will discuss how file-granular policies can sythesize
multiple keys to cryptographically protect files. For example, both
logon credentials and off-device keys can together preclude access.
This work represents efforts by Ildar Muslukhov.

I will also present the challenges involved in file name encryption on
a multi-tenant system and will discuss novel solutions spearheaded by
Uday Savagaonkar. This approach involves treating the user domain,
HTree domain, and disk domains for the file names separately and
applying different transformations depending upon whether or not the
encryption keys for the file names are available.

Finally, I will discuss what our future plans are with respect to
encryption with integrity, which will include leveraging ext4
transactions to enforce cryptographic consistency while managing
additional per-block authentication data.