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Remote Power Analysis of RFID TagsJoint work with Adi Shamir

yossi.oren[at]weizmann.ac.il28/Aug/06

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Abstract

• The RF power reflected by an RFID tag is dependent on its internal power consumption

• This property allows power analysis attacks to be performed over a distance

• In the short term, it can be used to extract the kill password of EPC tags

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Talk Structure

• Introduction to passive RFID

• Introduction to power analysis

• Our attack

• Countermeasures

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A Taxonomy of RFID Tags

• An RFID tag is a very simple computer, usually associated with a physical object

• Tags communicate with a powerful reader over a wireless link

• Tags can be active or passive• … can be inductively or radiatively coupled,

and work in a variety of operating frequencies• Have various levels of computing power• EPC tags: passive tags, radiatively

coupled, 900MHz, read/write memory

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Components of the EPC RFID System

Tag

• The reader has a powerful antenna and an external power supply

• The reader surrounds itself with an electromagnetic field

• The tag is illuminated by this field

Reader

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ReaderTag Data Exchange

Tag

• The reader sends commands to the tag via pulse amplitude modulation

• The tag sends responses to the reader via backscatter modulation

Reader

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ReaderTag Data Exchange

Tag

• The reader sends commands to the tag via pulse amplitude modulation

• The tag sends responses to the reader via backscatter modulation

Reader

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Do Tags Have Secrets?

• Most of the payload of today’s RFID tags is public – that’s what they’re for

• However, tags still have secrets!

• Today – EPC tags have secret access and kill passwords

• Tomorrow – cryptographic keys?

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An Introduction to power analysis

Toggle Flip-flop

VCCA

OUT

OscilloscopeOscilloscope

• Key observation – modern ICs consume more power when they switch between states

• Used by [Kocher et al. ‘99], others to attack cryptographic smart cards

5V

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Cracking passwords with power analysis

• We send the password to a secure device bit by bit

• The first wrong bit is very “exciting”

• Allows password to be recoverable in linear time

• Was used in practice to crack PIN codes on smart cards

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Previous work

• EM attacks ([van Eck ‘85], [Mangard ‘03])

• Attacks on RFID– Zapping [“Minime” et al. ‘05]– Jamming [Juels et al. ‘03], [Bolan ‘06]– Skimming [Kirschenbaum et al. ‘06]

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Our attack

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A Closer Look at Backscatter Modulation

TagReader

• The current flowing through the tag antenna results in an electromagnetic field

• Busy tag = More current = stronger field• We call this effect parasitic backscatter

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Lab setup – physical

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Lab setup – logical

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Overview of results

• Existence of parasitic backscatter

• Effect of power consumption on backscatter

• Full power analysis attack from backscatter

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Existence of parasitic backscatter (1)

• Trace shows the signal reflected from a Generation 1 tag during a kill command

• Tag is supposed to be completely silent• Is it? Let’s zoom in…

Power Time

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Existence of parasitic backscatter (2)

• The distinctive saw-tooth pattern is added by the tag to the clean reader signal

• Probably caused by tag’s power extraction circuit• We can show that “thirsty” tags reflect more power

Reflection from tag Original signal from readerPower Time

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Full power analysis attack from parasitic backscatter

• Recap: The first bad password bit is “very exciting”

• Experiment was done with one tag at a fixed location

• Tag was programmed with kill password “1111 1111”, then “0000 0001”

• In both cases we tried to kill it with the wrong password “0000 0000”

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Extracting one password bit

Here, the tag is expecting “1111 1111”

Here, it is expecting “0000 0001”

In both cases, tag gets “0000 0000”

Power Time

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Power analysis countermeasures

OscilloscopeOscilloscope

• Two main approaches:

– Mitigation: Lower the signal-to-noise ratio of the power trace

– Prevention: Completely decorrelate power consumption from internal state

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Mitigation countermeasures

• Common approach: add noise to power consumption

• Problematic to add to tag

• Problematic to add to reader

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Prevention countermeasures

• Common approach: consume the same amount of power every clock cycle

• Problem: Power consumption is always worst case

• Increases tag cost, reducesits usable range

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Double-buffering power supply

Tag LogicTag Logic

Power Extraction

• Decouple power supply from consumers• Compatible with current RF front ends• Requires no modifications to tag’s control circuit

Power Extraction

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Closing Remarks

• Power analysis attacks come from the world of smart cards

• The rules of the market for RFID tags are not the same as the one for smart cards

• Power analysis threat should be understood and publicized, or nobody will do anything about it

26The authors wish to thank Mickey Cohen, Ari Juels, Simon Krausz, Oded Smikt, Eran Tromer, Amir Yakoby, Oren Zarchin and the many other people who shared their knowledge, time and equipment and helped this research take shape.The authors wish to thank Mickey Cohen, Ari Juels, Simon Krausz, Oded Smikt, Eran Tromer, Amir Yakoby, Oren Zarchin and the many other people who shared their knowledge, time and equipment and helped this research take shape.

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It’s all scratch slides from here on

• You really want to exit the slide show…

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• TU Graz site, August 2005:

Almost previous work?

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Double-buffering power supply

• Decouple power supply from consumers• Compatible with current RF front ends• Requires no modifications to tag’s control circuit

Power Extraction

Tag LogicTag Logic

Power Extraction

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Double-buffering power supply

• Decouples power supply from consumers• Compatible with current RF front ends• Requires no modifications to tag’s control circuit

Tag Logic

Power Extraction

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Double-buffering power supply

• Decouple power supply from consumers• Compatible with current RF front ends• Requires no modifications to tag’s control circuit

Power Extraction

Tag Logic

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Double-buffering power supply

• Decouple power supply from consumers• Compatible with current RF front ends• Requires no modifications to tag’s control circuit

Power Extraction

Tag Logic

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Scratch

TagReader

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Scratch 2

TagReader

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Scratch 3

Tag

• The reader has a powerful antenna and a power supply

• The reader surrounds itself with an electromagnetic field

• The tag is illuminated by the field, providing it with power

Reader

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Scratch 4