Physical Design Security

Physical Design Security

Purpose

Review physical implementation for security vulnerabilities arising from power domain coupling, timing-related leakage, clock domain crossing issues, and layout-level information exposure.

Scope Constraints

Reads physical design files, floorplans, and hardware specifications. Does not modify design files or execute EDA tools. Does not access foundry-specific restricted data.

Inputs

• Physical design constraints and floorplan
• Power domain architecture (voltage islands, power gating, level shifters)
• Clock domain architecture (clock trees, domain crossings, gating)
• Security-sensitive blocks and their physical placement
• Threat model for physical attacks (invasive, semi-invasive, non-invasive)

Input Sanitization

No user-provided values are used in commands or file paths. All inputs are treated as read-only analysis targets.

Procedure

Step 1: Review Physical Implementation Constraints

Map the physical design from a security perspective:

• Identify security-critical blocks and their placement relative to chip boundaries
• Review floorplan for isolation between security domains
• Check that sensitive blocks are not adjacent to untrusted I/O or analog blocks
• Verify that security-critical paths meet timing with margin (no hold violations that could cause glitches)

Step 2: Identify Timing-Related Leakage

Assess timing paths for information leakage:

• Variable-latency operations in security-critical paths (data-dependent timing)
• Setup/hold violations that create intermittent behavior exploitable by fault injection
• Timing margin on security-critical paths (can voltage/temperature manipulation cause failures?)
• Early/late path analysis for security-relevant signals

Step 3: Check Power Domain Isolation

Review power architecture for security:

• Power domain boundaries align with security domain boundaries
• Level shifters between security domains do not create information leakage paths
• Power gating sequences do not expose security state during transitions
• Decoupling capacitors and power grid design minimize data-dependent power signatures
• Isolated power supplies for security-critical blocks (crypto engines, key storage)

Step 4: Verify Clock Domain Crossing Security

Review clock domain crossings (CDCs) near security logic:

• Synchronizers on all signals crossing between clock domains near security boundaries
• No metastability windows that could cause security checks to be bypassed
• Clock gating does not create windows where security monitors are inactive
• Glitch filters on security-critical asynchronous inputs

Step 5: Assess Physical Attack Resistance

Evaluate the design against physical attack vectors:

• Power analysis (DPA/SPA): Are crypto operations power-balanced? Are there masking countermeasures?
• EM emanation: Are sensitive blocks shielded? Is routing of key material minimized?
• Fault injection: Are voltage glitch detectors present? Are laser fault injection countermeasures in place?
• Probing: Are metal layers over key storage sufficient? Are mesh sensors present?

Compaction resilience: If context was lost during a long session, re-read the Inputs section to reconstruct what system is being analyzed, then resume from the earliest incomplete step.

Output Format

Physical Security Domain Map

┌─────────────────────────────────────┐
│ Power Domain: [Name]                │
│ Clock Domain: [Name]                │
│                                     │
│  ┌─────────┐     ┌──────────┐      │
│  │ [Block]  │────→│ [Block]  │      │
│  └─────────┘     └──────────┘      │
│         │ CDC                       │
│         ▼                           │
│  ┌─────────────┐                   │
│  │ [Sec Block]  │ ← Isolated power │
│  └─────────────┘                   │
└─────────────────────────────────────┘

Physical Security Finding Table

Residual Physical Risk Summary

• [Risk]: [Why accepted] — [Monitoring/detection approach]

Handoff

• Hand off to rtl-security-review if RTL changes are needed for physical security findings.
• Hand off to microarch-analysis if microarchitectural mitigations are required based on physical analysis.

Quality Checks

• All security-critical blocks are identified in the floorplan
• Power domain boundaries are verified to align with security domains
• Clock domain crossings near security logic are reviewed for metastability
• Timing margins on security-critical paths are assessed
• Physical attack resistance is evaluated (power analysis, EM, fault injection, probing)
• Power gating sequences are reviewed for security state exposure
• Recommendations include specific physical design changes

Evolution Notes