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fyi: ECDAA: Fixing TPM 2.0 for Provably Secure Anonymous Attestation

From: =JeffH <Jeff.Hodges@KingsMountain.com>
Date: Mon, 31 Jul 2017 08:49:28 -0700
To: W3C Web Authn WG <public-webauthn@w3.org>
Message-ID: <7de5ec25-c628-6ac6-d53e-729626069025@KingsMountain.com>
Of possible interest...

One TPM to Bind Them All: Fixing TPM 2.0 for Provably Secure Anonymous 
Jan Camenisch, Liqun Chen, Manu Drijvers, Anja Lehmann, David Novick, 
Rainer Urian

The Trusted Platform Module (TPM) is an international standard for a 
security chip that can be used for the management of cryptographic keys 
and for remote attestation. The specification of the most recent TPM 2.0 
interfaces for direct anonymous attestation unfortunately has a number 
of severe shortcomings. First of all, they do not allow for security 
proofs (indeed, the published proofs are incorrect). Second, they 
provide a Diffie-Hellman oracle w.r.t. the secret key of the TPM, 
weakening the security and preventing forward anonymity of attestations. 
Fixes to these problems have been proposed, but they create new issues: 
they enable a fraudulent TPM to encode information into an attestation 
signature, which could be used to break anonymity or to leak the secret 
key. Furthermore, all proposed ways to remove the Diffie-Hellman oracle 
either strongly limit the functionality of the TPM or would require 
significant changes to the TPM 2.0 interfaces. In this paper we provide 
a better specification of the TPM 2.0 interfaces that addresses these 
problems and requires only minimal changes to the current TPM 2.0 
commands. We then show how to use the revised interfaces to build q-SDH- 
and LRSW-based anonymous attestation schemes, and prove their security. 
We finally discuss how to obtain other schemes addressing different use 
cases such as key-binding for U-Prove and e-cash.

### from the introduction:
Some of the changes to the TPM 2.0 interfaces we propose have already 
been adopted by the TCG and will appear in the forthcoming revision of 
the TPM 2.0 specifications. The remaining changes are currently under 
review by the TPM working group. Furthermore, the authors are in 
discussion with the other bodies standardizing DAA protocols to adopt 
our changes and schemes, in particular ISO w.r.t. to ISO/IEC 20008-2, 
Intel for EPID, and with the FIDO alliance for their specification of 
anonymous attestation [CDE+], so that all of these standards will define 
provably secure protocols that are compatible with each other
[CDE+],  Jan Camenisch, Manu Drijvers, Alec Edgington, Anja Lehmann, 
Rolf Lindemann, and Rainer Urian.
FIDO ECDAA algorithm, implementation draft.
Received on Monday, 31 July 2017 15:49:59 UTC

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