Enhancing Physical Security for Cryptographic Modules

1. NIST CMVP Physical Security Conference Physical Security Protections September 25, 2005

2. Introduction Physical Security Considerations Attack Considerations Commonly Used Physical Security Protections Multi-Chip Embodiments Attack Challenges Attack Tools and Methods Conclusion Agenda

3. Physical Security Considerations • Module Physical Security Considerations: • Protection features are dependant on: • Sensitivity of the information it is protecting • Deployment environment • FIPS 140-2 Level 1 & 2: • The dependability of cryptographic modules is reliant upon all of the elements and the interactions of the physical security system. • FIPS 140-2 Levels 3 & 4 • Highly sensitive, but no classified, information • As the deployment environment becomes more hostile, the integrity of the module relies heavily on the detection and possible prevention of unauthorized physical access.

4. Attack Considerations • The physical security characteristics and mechanisms integrated in cryptographic modules (security or cryptographic) are an independent component that should effectively protect against potential penetration attacks deemed reasonable and appropriate for their given deployment environment. • The components that devise the physical security system must work together in unison and be of comparable strength. • If any component of the system is weak or works ineffectively with any of the other components, then that component has the potential of causing an overall physical security system weakness. • Attackers typically research and investigate these system weaknesses and tailor an exploit to take advantage of this vulnerability to compromise cryptographic module.

5. Physical Security Protection • Three commonly used physical security protections: • Potting Encapsulation • Enclosure with tamper switches • Enclosure with tamper wrapper

6. General Attack Challenges • Visibility • Structure of the module and functionality • Accessibility • Highest probability areas to initiate compromising vulnerabilities • Ability • Knowledge of physics, electronics, and material properties • Experience to utilize the optimum tools, supplies, and resources at the appropriate time

7. Potting Encapsulation • Completely surrounds the cryptographic boundary • Requirements for compliance • Opacity (or inability to see through the potting material); • Visible tamper evidence if removed; • Sufficiently “hard” after properly cured • Only sufficient to meet level 3

8. Potting Encapsulation Attacks • Potting encapsulations are typically compromised with Heat or Solvents without causing damage to the underlying circuitry • Mechanical methods may also be effective Note: These attack methods are only applicable for Level 4 modules

9. Enclosures and Tamper Switches • Tamper switches are the most common mechanisms used to protect modules with metallic and/or plastic enclosures • Tamper switches prevent unauthorized access by detecting an opening of the module’s cover and/or doors • Upon detection, the module responds by zeroizing all plaintext critical security parameters • Zeroization leaves the module and its information virtually without value

10. Enclosures and Tamper Switches • Variety of Tamper Switches (sample of most common) • Micro-switches are the most basic switch. These types of switches are engaged when the module’s enclosure (covers and/or doors) are closed and force is applied. When the enclosure is opened, the switch releases, which in turn causes a tamper event. • Pressure contacts function in a similar manner as the micro-switch. With this approach, there are typically two conductive pads designed on a PCB board (rather than a separate component). When the module’s covers/doors are closed, the two pads become shorted typically by a conductive membrane (commonly seen in keypads). When the enclosure is opened, the conductive membrane no longer provides the conductive link between the two pads, creating an open circuit, and causing the module to respond with a tamper event. • Reed switches respond to the polarity of a magnetic source in close proximity. Typically, the module’s enclosure is fixed with a magnet to engage a reed switch, which is mounted on the module’s PCB. When the enclosure is opened, the magnetic source moves further apart from the reed switch, eventually causing a tamper event.

11. Enclosures and Tamper Switch Attacks • Tamper switches are extremely easy to defeat. • Challenge largely depends on whether or not the objective is to limit or have no visible evidence of tamper. Note: The testing limitations (e.g., no drilling, milling, grinding, or dissolving) for FIPS 140-2 Level 3 make tamper switches an acceptable solution. However, the testing limitations are removed on FIPS 140-2 Level 4, so in order to achieve compliance would require additional security features

12. Enclosures and Tamper Wrappers • A tamper wrapper is a flexible film that has conductive traces on it, used to fully enclose the cryptographic module • Depending on the material and the characteristics a tamper wrapper can also protect against a variety of other attacks, including:chemicals, heat, cutting, grinding, and drilling

13. Enclosures and Tamper Wrappers • Strength Differentiators: • Number of tamper layers within the film; • Width and distance between traces; • Visibility of the traces; • Trace material • Folding/wrapping methodology • Two commonly deployed tamper wrappers • Copper - relatively durable against mechanical, chemical, and high temperature based attacks • Conductive Ink – more sensitive then copper based solutions • Tamper wrappers that exhibit high impedance characteristics are typically harder to defeat because of their ability to monitor a change in voltage potential when attacked

14. Enclosures and Tamper Wrapper Attacks Visibility & Accessibility: • Mechanical tools • Chemical exposure • Abrasives • Electrical blasters • Heat exposure • X-Ray • Statically charge the conductive traces • Heat dissipation

15. Physical Security ProtectionsConclusion • Physical attacks are possible • Tools available at hardware and hobby stores • Less than $100 USD • FIPS 140-3 Considerations: • Decrease laboratory testing limitations at Level 3