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ClkScrew
Aaron Zhang
Outline
- Introduction to DVFS and background information.
- What makes CLKSCREW unique?
- Challenges to CLKSCREW
- Attacks and Results
- Conclusion
ClkScrew Aaron Zhang Outline Introduction to DVFS and background - - PowerPoint PPT Presentation
ClkScrew Aaron Zhang Outline Introduction to DVFS and background - - PowerPoint PPT Presentation
ClkScrew Aaron Zhang Outline Introduction to DVFS and background information. What makes CLKSCREW unique? Challenges to CLKSCREW Attacks and Results Conclusion Voltage Energy + = Usage Frequency HARDWARE DVFS (Dynamic
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Voltage Frequency + = Energy Usage
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HARDWARE SOFTWARE
DVFS (Dynamic Voltage and Frequency Scaling)
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Outline
- Introduction to DVFS and background information.
- What makes CLKSCREW unique?
- Challenges to CLKSCREW
- Attacks and Results
- Conclusion
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FLIP FLOP FLIP FLOP
1 1 1
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FLIP FLOP FLIP FLOP
1 Less time for number to go through Flip-Flop
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TRUSTZONE NON- TRUSTZONE
DVFS
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- 1. Clear Residual States
- 2. Profile for Anchor
- 3. Pre-fault Delaying
- 4. Deliver the fault.
Steps
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Outline
- Introduction to DVFS and background information.
- What makes CLKSCREW unique?
- Challenges to CLKSCREW
- Attacks and Results
- Conclusion
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Do phones allow for overclocking/ under-volting?
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How do you make sure the flip-flops do not damage the injected code?
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CPU CORE 1 CPU CORE 2
Attacker Code Victim Thread
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How do you get the timing precise enough? How do we make sure the attack
- ccurs where we want it to
- ccur?
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Outline
- Introduction to DVFS and background information.
- What makes CLKSCREW unique?
- Challenges to CLKSCREW
- Attacks and Results
- Conclusion
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TRUSTZONE NON- TRUSTZONE
DVFS
Inferring AES Keys
AES Decryption Attacking Code
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TRUSTZONE NON- TRUSTZONE
DVFS
Loading Apps into Trust Zone
Attacker’s App Attacking Code
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App
1. Signature 1 2. Signature 2 3. Signature 3 4. Signature 4
- Each App has 4 Signatures
- One signature takes 270
Million clock cycles to validate.
- In order for CLKSCREW to
corrupt data it needs to change just 65 thousand clock cycles within the entire process
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65000/1080000000 = 0.0000601%
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Cache Profiling
- Pick a memory address of the area of interest
- Run dummy instructions and time the amount it
takes for these instructions to be removed
- Patterns for removing will tell you the pattern of
the actual code. Timing Anchor
- Track duration of consecutive cache instructions
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One instance of Desired Fault out of 65
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Outline
- Introduction to DVFS and background information.
- What makes CLKSCREW unique?
- Challenges to CLKSCREW
- Attacks and Results
- Conclusion
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Defenses
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Hardware Limits regarding Voltage and Frequency
- Make it unable for users to overclock and under-
volt their phones
- Difficulties include having to remake hardware
chips from scratch and having every phone and chipmaker adhere to regulation.
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Separate DVFS for Trustzone
- Create a separate DVFS for Trustzone itself
- Separate DVFS’ for cores on the same chip can
cause massive overhead.
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Randomization
- Randomize clock cycles so that attackers do not
know what to expect.
- Useless when run-time time-anchors are used.
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Conclusions
- CLKSCREW is a side-channel attack that utilizes voltage and frequency
- f devices to induce faults.
- Exploiting faults that cannot be easily changed.