The document discusses secure embedded systems as a requirement for cyber physical systems and the internet of things. It begins by providing examples of attacks on modern embedded systems like cars, industrial control systems, smart grids, and medical devices. It then discusses trends increasing security risks for embedded systems like network connectivity and standardization. Finally, it outlines requirements for future secure embedded systems and describes techniques like hardware security modules, secure elements, physical unclonable functions, and trusted operating systems to provide security in embedded systems going forward.

1. Technische Universität München
Secure Embedded Systems
eine Voraussetzung für Cyber Physical Systems und das Internet der Dinge
Kolloquium der Fakultät 5 der Universität Stuttgart
17. Dezember 2013
Prof. Dr.-Ing. Georg Sigl
Lehrstuhl für Sicherheit in der Informationstechnik
Technische Universität München
Fraunhofer Institut für Angewandte und Integrierte Sicherheit AISEC

2. Technische Universität München
Content
• Attack examples on embedded systems
• Future secure embedded systems
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3. Technische Universität München
ATTACKS ON EMBEDDED
SYSTEMS
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4. Technische Universität München
Attacks on modern cars
Comprehensive Experimental Analyses of Automotive Attack Surfaces
S. Checkoway, D. McCoy, B. Kantor, D. Anderson, H. Shacham, S. Savage, K.
Koscher, A. Czeskis, F. Roesner, T. Kohno. USENIX Security, August 10–12, 2011.
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5. Technische Universität München
Attacks on industrial control systems: Stuxnet
http://www.faz.net/aktuell/feuilleton/debatten/digitales-denken/trojaner-stuxnet-der-digitaleerstschlag-ist-erfolgt-1578889.html
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6. Technische Universität München
Attacks on industrial control systems
Source: http://www.bhkw-infothek.de/nachrichten/18555/2013-04-15-kritische-sicherheitsluckeermoglicht-fremdzugriff-auf-systemregler-des-vaillant-ecopower-1-0/
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7. Technische Universität München
Attacks on smart grid through smart meter
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8. Technische Universität München
Attacks on medical devices
Source: http://media.blackhat.com/bh-us-11/Radcliffe/BH_US_11_Radcliffe_Hacking_Medical_Devices_Slides.pdf
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9. Technische Universität München
Product Piracy
• Estimated damage in machine
construction industry (source VDMA)
– 7.9 Billon Euro (~4% of revenue)
• Steps of pirates
– HW Component identification
– Software extraction
– Rebuilding hardware
– Cloning software
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10. Technische Universität München
Trends increasing the security risks
• Network connection
– ES can be attacked through network
– Insecure system
 remote attacks
 attacked through
unprotected ES
 malware
• Standardization in software
– Operating systems (e.g. Linux)
– Web browsers
• Platform design with software configurability  jail break, tuning
• Concentration of multiple functions (multicore)  separation risk
• Significant Know-How in ES
 product piracy
• Hacker = product owner
 hardware attacks
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11. Technische Universität München
Threads in Cyber Physical Systems
Network and
Backgroud Systems
Attacks through
broken embedded systems
Attacks out of Cyberspace
Embedded System
BMBF-FKZ: 01IS13020
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12. Technische Universität München
FUTURE SECURE
EMBEDDED SYSTEMS
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13. Technische Universität München
Requirements for future secure embedded systems
1.
2.
3.
4.
Security for more than 10 years (target 30 years)
Secure machine to machine communication (M2M)
Protection of embedded systems against manipulation and misuse
Fulfillment of typical non functional requirements, i.e.:
– Real time behavior
– Resource limitations (cost, power)
5. Maintain security despite of increasing complexity
6. Protection of intellectual property
7. Secure software update during operation
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14. Technische Universität München
Secure embedded system
M2M
other System on Chip
SIM
ID
Actuator
GSM
Trust
Core 1 OS Core 2
Core i
System on Chip
Core n
IO-interfaces
RAM
Flash
ID
Sensor
Peripherals
Hardware
Security
Module
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15. Technische Universität München
Secure embedded system: Chip Identities
M2M
other System on Chip
SIM
ID
Actuator
GSM
Trust
Core 1 OS Core 2
Core i
System on Chip
Core n
IO-interfaces
RAM
Flash
ID
Sensor
Peripherals
Hardware
Security
Module
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16. Technische Universität München
IDs for Hardware
• Binding of components
– Authentication
– Integrity checking
• Piracy protection
– Encryption with derived keys
• Methods
– Physical Unclonable Functions
(PUF) : fingerprint of a chip
– Fuses (electric or laser)
– Flash memory
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17. Technische Universität München
PUFs as security primitive
„Unique“
Physical Property
+
Measurement
Method
=
Authentication,
Key Generation
PUF
+
=
Physical
Unclonable
Function
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18. Technische Universität München
Ring Oscillator PUF (Suh and Devadas, 2007) *
• Ring oscillator frequencies depend on manufacturing variations
• Two ROs are compared to obtain a response bit
* G. E. Suh and S. Devadas. Physical unclonable functions for device authentication and secret key
generation. Design Automation Conference, 2007. DAC ’07. 44th ACM/IEEE, pages 9–14, 2007.
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19. Technische Universität München
SRAM PUF (Guajardo et al., 2007) *
• Symmetric circuit balance influenced by manufacturing variations
• SRAM cells show a random, but stable value after power-up
* J. Guajardo, S. S. Kumar, G. J. Schrijen, and P. Tuyls. FPGA intrinsic PUFs and their use for IP
protection. In CHES 2007, volume 4727 of LNCS, pages 63–80. Springer, 2007
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20. Technische Universität München
Automotive ECUs today and in future
Microcontroller
Microcontroller
NVM
RAM
Code
key
CPU
Code
application
PUF
key
Embedded Flash
65nm √
40nm √
28nm ?
???
CPU
application
Flash
Encrypted Code/Data
Logic Process + external Flash
+ Shrinkable
+ Lower Cost
+ Higher Performance
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21. Technische Universität München
Alternatives to PUF based key generation
Microcontroller
RAM
• Fuses
– Electrical
• Reliability: weak
Code
key
CPU
application
– Laser
• Size: very large
• Security: Easy to identify and modify
Flash
Encrypted Code/Data
• OTP (one time programmable memory)
– Cost: comparison with PUF technology open
– Security: memory cells easier to detect, extract and modify
– Programming of key during test increases test complexity
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22. Technische Universität München
Reliability of PUFs
• Critical parameters:
– Temperature
– Voltage
– Ageing
• Countermeasures:
– Differential measurement
– Redundancy: Selection of reliable bits (1000 PUF Bits  100
Key Bits)
– Proper design: Design and design parameters must consider
the behavior of temperature and voltage variations as well as
ageing (as for any other circuit design)
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23. Technische Universität München
Frequency behavior of an oscillator PUF
f
Osc 3
instable
Osc 4
f
Osc 1 good
Osc 2
f
Osc 5
Osc 6
-40°C
25°C
Critical:
uniqueness may
be compromised
150°C
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24. Technische Universität München
State of the Art in error correction
Encoded Key Bits
PUF Bits:
- Reliable 1
- Reliable 0
- Unreliable
PUF Response
Block Borders
Helper Data
u =1
index of selected bit 1
u2=?
u3=3
• All error correctors work on fixed block structure:
e.g. IBS (Yu and Devadas, 2010 *)
• Goal: find one white and one black square in each block of four
• Helper data store the indices of selected bits
* M.-D. Yu and S. Devadas, Secure and robust error correction for physical unclonable functions,
IEEE Design & Test of Computers, vol. 27, no. 1, pp. 48-65, 2010
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25. Technische Universität München
Differential Sequence Coding *
Encoded Key Bits
PUF Response
Helper Data
- distance
- inversion
•
•
•
•
No fixed block borders
Helper data store distance to next bit and an inversion indicator
Larger blocks of unreliable bits can be skipped
Most efficient error corrector scheme known to date
* M. Hiller, M. Weiner, L. Rodrigues Lima, M- Birkner and G. Sigl. Breaking through Fixed PUF
Block Limitations with Differential Sequence Coding and Convolutional Codes, TrustED, 2013
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26. Technische Universität München
Components of a PUF key store
Challenge
Ci
•
•
•
•
•
Physical
System
Response
Error
Correction
S RCi E
Challenge:
Physical System:
Response:
Error Correction:
Hash Function:
Hash
Function
Helper Data
(Public)
Key
H K
Power-On for SRAM, Ring-Oscillator selection
SRAM, Ring-Oscillators
Stream of Bits
Using public helper data to increase reliability
Removes bias in the key bit distribution
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27. Technische Universität München
Secure embedded system: Secure Elements
M2M
other System on Chip
SIM
ID
Actuator
GSM
Trust
Core 1 OS Core 2
Core i
System on Chip
Core n
IO-interfaces
RAM
Flash
ID
Sensor
Peripherals
Hardware
Security
Module
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28. Technische Universität München
Tasks of Secure Elements
•
•
•
•
•
•
•
•
Key storage
Asymmetric cryptography (signing and encryption)
Session key generation
Random number generation
Access right check
Integrity check
Attestation
Secure data storage
• Resistance against Hardware attacks!
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29. Technische Universität München
Secure Element in a vehicle
• In BMBF Project SEIS (Sicherheit in eingebetteten IP-basierten
Systemen) AISEC integrated a Secure Element in a car.
Internet
Gateway
OEM
Server
Secure Element
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30. Technische Universität München
Secure Element in Smart Meter
The BSI Protection Profile
requests a Secure Element in the
Smart Meter Gateway.
Secure
Element
Source: Protection Profile für das Gateway eines Smart Metering Systems; http://www.bsi.bund.de
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31. Technische Universität München
Secure Smart Meter
• Java 3.0 Secure Element in Smart Meter
– All security functions enclosed
– Communication end point
• Gateway
– Memory (encrypted)
– Display
– Communication channels
• Advantages:
– High Security through Hardware
Secure Element
– Easier certification
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32. Technische Universität München
Secure Elements in mobile phones
3 Secure Elements
• SIM
• Security Chip
• Secure SD Card
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33. Technische Universität München
Secure embedded system: Secure Software
M2M
other System on Chip
SIM
ID
Actuator
GSM
Trust
Core 1 OS Core 2
Core i
System on Chip
Core n
IO-interfaces
RAM
Flash
ID
Sensor
Peripherals
Hardware
Security
Module
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34. Technische Universität München
Trusted OS
• Trusted execution environment in the system controller
• Virtualisiation for application separation
• Integration of a hardware secure elements as trust anchor
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35. Technische Universität München
Trusted OS: Linux Containers (Trust|Me)
Idea: Sandboxed Android using container-based isolation
–
Remote device administration
–
–
Remote access using ssh and other Linux utilities
Storage
–
–
Transparent file encryption (device or file based)
–
–
Filesystem snapshots and recovery
File integrity protection using Linux Security Modules (LSM)
Network
–
–
Transparent tunneling using Virtual Private Networks (VPN)
Graphical User Interface (GUI)
–
Secure display (indicated by LED) and secure input (hardware buttons)
–
Secure PIN entry used to unlock SE in microSD card (key storage)
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36. Technische Universität München
Thank You
georg.sigl@aisec.fraunhofer.de
sigl@tum.de
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