![](bg9.png)
Currently anyone in possession of the public b
key
can provide Application Updates, which is a known
weakness in TPM-based secret distribution (Toegl
et al., 2008). We recommended to share an addi-
tional authentication secret between the Vendor and
the TPM. The upcoming version 2.0 TPM will pro-
vide functionality for signature verification (TCG,
2013b), thus allowing the authentication of update
origins.
8 CONCLUSIONS
In section 3 we introduced “GUSTL” a novel embed-
ded Trusted Computing hardware platform, intended
for use in research on low-resource trusted embedded
system. Our platform integrates a typical embedded
micro-controller, as it may be used in embedded con-
trol applications or sensor nodes, with a Trusted Plat-
form Module. Our hardware platform complements
more powerful Linux- and Android-based trusted em-
bedded systems, by providing a research platform for
Trusted Computing on small, low-resource embedded
systems.
Based on the hardware developed, we provided
a proof-of-concept implementation of embedded
trusted software to demonstrate that Trusted Comput-
ing mechanisms are possible and useful for assessing
firmware, even on systems with very little memory
and processing power. The use-case for this proof-
of-concept implementation is measured firmware up-
date. In section 4 we show how to realize firmware
measurements based on Trusted Computing on a low-
resource micro-controller platform. Moreover we dis-
cuss a trusted firmware update scheme, which effec-
tively leverages the security and cryptography ser-
vices of an embedded Trusted Platform Module, to
trustworthily distribute diversified firmware update
keys to individual target devices. Our firmware
update scheme only requires the embedded micro-
controller to provide standard symmetric cipher and
hash primitives. Asymmetric cryptography primi-
tives are solely handled by the TPM, and can be seen
as “black-box” from the microcontroller’s point of
view. We used the TPM to store measurements, and
to secure the device startup as well as updates of the
firmware. We showed that it is possible to not only
protect the intellectual property of the running Ap-
plication but also the embedded platform itself from
unauthenticated Application Updates.
Based on the results we conclude that even very
small systems can already profit from current gen-
eration Trusted Platform Modules. The proposed
firmware distribution approach offers significant im-
provements for the protection of intellectual proper-
ties in industrial contexts. Trusted Computing fea-
tures originally intended for PCs and servers are a
promising approach to small Embedded Systems.
ACKNOWLEDGEMENTS
This work was supported by the EC, through projects
FP7-ICT-SEPIA, grant agreement number 257433,
project FP7-ICT-STANCE, grant agreement number
317753. We thank Florian Schreiner, Infineon AG for
providing the embedded TPM samples.
REFERENCES
Atmel (2012). 8-bit atmel xmega au manual, revision f.
Atmel (2013). Atmel software framework.
Chen, L., Landfermann, R., L¨ohr, H., Rohe, M., Sadeghi,
A.-R., and St¨uble, C. (2006). A protocol for property-
based attestation. In Proceedings of the First ACM
Workshop on Scalable Trusted Computing, STC ’06,
pages 7–16, New York, NY, USA. ACM.
Feller, T., Malipatlolla, S., Meister, D., and Huss, S. (2011).
Tinytpm: A lightweight module aimed to ip protection
and trusted embedded platforms. In 2011 IEEE Inter-
national Symposium on Hardware-Oriented Security
and Trust (HOST), pages 6–11.
Global Industry Analysts Inc. (2013). Embed-
ded Systems: Market Research Report.
http://marketpublishers.com/.
Hendricks, J. and van Doorn, L. (2004). Secure bootstrap
is not enough: shoring up the trusted computing base.
In Proceedings of the 11th workshop on ACM SIGOPS
European workshop. ACM.
Hwang, D., Schaumont, P., Tiri, K., and Verbauwhede, I.
(2006). Securing embedded systems. Security Pri-
vacy, IEEE, 4(2):40–49.
Kizhvatov, I. (2009). Side channel analysis of avr xmega
crypto engine. In Proceedings of the 4th Workshop on
Embedded Systems Security, WESS ’09, pages 8:1–
8:7. ACM.
Koopman, P. (2004). Embedded system security. Computer,
37(7):95–97.
Larbig, P., Kuntze, N., Rudolph, C., and Fuchs, A. (2013).
On the integration of harware-based trust in embedded
devices. Konferenz f¨ur ARM-Systementwicklung.
Mueller, T. (2008). Trusted Computing Systeme. Springer.
NXP semiconductors (2012). I2C-bus specifica-
tion and user manual. Available online at:
http://www.nxp.com/documents/user
manual/
UM10204.pdf.
Papa, S., Casper, W., and Nair, S. (2011). Placement
of trust anchors in embedded computer systems. In
2011 IEEE International Symposium on Hardware-
Oriented Security and Trust (HOST), pages 111–116.
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