SPA and DPA

1. SPA and DPA Possible Testing Solutions and Associated Costs Stan Kladko, Ph. D., BKP Security Labs

2. Introduction • Simple Power Analysis (SPA) and Differential Power Analysis (DPA) • Introduced by P. Kocher, J. Jaffe, and B. Jun • Can be potentially used to compromise keys and critical security parameters

3. SPA and DPA • Simple power analysis requires measurement and observation of time-resolved power traces • Differential power analysis includes statistical sampling and analysis of correlations • Other physical characteristics can be used such as intensity of electromagnetic emissions (EMA)

4. SPA and DPA • Do not require expensive equipment and are relatively easy to implement • Descriptions of techniques and experimental setups are readily available

5. Proposed Countermeasures • Physical shielding • Random power consumption elements • Randomizing algorithm execution • Randomizing circuit timing • Interleaving code with dummy instructions • Redesigning cryptographic algorithms • Redesigning circuit layouts • …

6. FIPS 140-2 • Currently lacks SPA and DPA requirements • This makes it somewhat outdated as a security standard, in particular for smartcards • Adding SPA and DPA requirements could be a logical step to consider for FIPS 140-3

7. FIPS 140-2 Security Levels • Level 1 – no significant physical security requirements • Level 2 – tamper evidence or ability to detect key compromise • Level 3 and Level 4 – key destruction in case of compromise

8. FIPS 140-2 Security Levels • SPA and DPA = key compromise without traces of tampering • Level 2 seems to be appropriate

9. FIPS 140-2 Module Types • single-chip (e.g. smartcard) • multiple-chip embedded (crypto accelerator card) • multi-chip standalone (router or PC) • most published SPA/DPA attacks – single chip modules • SPA/DPA requirements could be limited to single-chip modules only

10. Testing Lab Considerations • Typical FIPS 140-2 testing costs < $50K • Assuming 20% of total costs one has $5K-10K for SPA/DPA testing • 1-2 person/weeks • Typical equipment items: digital oscilloscope, DC power supply, function generator, PC. • Total < $5K

11. SPA/DPA Testing Requirements • Simple • Reproducible • Standard experimental setup across labs • Standard testing methods for each Approved algorithm • Standard software (could be developed by NIST)

12. Staff Training • Need staff members familiar with applied physics and electrical engineering concepts • DPA requires familiarity with a number of concepts in statistics • NVLAP Handbook 150-17 for CMVP labs would need to be revised to include SPA/DPA training requirements

13. Criteria for SPA/DPA requirements • Simple criteria should be preferred • Having to analyze all measures and countermeasures would put undue burden on the lab • Physically measurable criteria would be preferred • Many papers list signal-to-noise ratio as a sensible criterion

14. Criteria for SPA/DPA requirements • The exact definition of the signal-to-noise ratio would be left to experts • Could be different for SPA vs. DPA • Any signal-to-noise ratio definition would not guarantee security due to feasibility of various noise-cancellation techniques • Signal-to-noise threshold could deter attackers with low attack potential

15. Summary • Adding SPA/DPA requirements to future versions of FIPS 140 seems justified • Candidate testing requirements shall be reviewed to assess potential implications for labs and vendors • Simple and well-defined requirements are preferred