veyepar: Clevis and Tang: securing your secrets at rest

Author(s):	Fraser Tweedale
Location	Room 8
Date	jan Wed 15	Days Raw Files
Start	14:25	First Raw Start	error-in-template
Duration	0:45:0	Offset	None
End	15:10	Last Raw End
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https://lca2020.linux.org.au/schedule/presentation/29/
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assets release.pdf Clevis_and_Tang_securing_your_secrets_at_rest.json
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Full disk encryption and, more generally, encryption of secrets at
rest are essential tools in the security toolbox.  But deploying
encryption at rest can have costs: latency (downtime), repetition
(productivity loss), proneness to error (typos; "was that '1' or
'l'?"), challenges in supplying a passphrase when needed (e.g.
headless systems).  Automated decryption often relies on delivery of
escrowed keys (a third party knows your secret).

We can do better.

_Tang_ [1] is a protocol and (along with the client-side program
_Clevis_ [2]) software implementation of *network bound encryption*;
that is, automatic decryption of secrets when a client has access to
a particular server on a secure network.  It uses McCallum-Relyea
exchange, a two-party key computation protocol based on Diffie-Hellman
where only the client can compute the key!  _Clevis_ [2] uses the
amazing *Shamir's Secret Sharing* algorithm to implement unlock
policies with thresholds that can include passphrases, Tang servers
and TPM-sealed secrets.

In this talk I will outline the use cases, explain the algorithms
and demonstrate these tools.  The live demo will set up a machine to
automatically decrypt a LUKS volume when a required number of Tang
servers are available.  I will conclude with a discussion of
limitations, assumptions and threats.

[1] https://github.com/latchset/tang
[2] https://github.com/latchset/clevis

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