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#   
Security &amp; Safety Features

## Sensor Hub (Sub-Hub) Scope Only

## 1 Feature Overview

The **Security &amp; Safety Features** ensure that the Sensor Hub operates only with trusted firmware, protects sensitive data at rest, and guarantees confidentiality and integrity of all communications. These features are foundational and cross-cutting, supporting all other functional features (DAQ, DQC, COM, DIAG, DATA, OTA).

This feature set is designed to:

*   Prevent execution of unauthorized or malicious firmware
    
*   Protect firmware, configuration, and machine constants stored in memory
    
*   Secure all communications with cryptographic mechanisms
    
*   Provide deterministic and auditable behavior in case of security violations
    

## 2 Scope and Assumptions

**In Scope**

*   Sensor Hub (ESP32-S3–based)
    
*   Boot process security
    
*   Flash and external storage protection
    
*   Communication security with Main Hub and peer Sensor Hubs
    

**Out of Scope**

*   Cloud server security policies
    
*   User identity management
    
*   Physical tamper detection hardware (optional future feature)
    

## 3 Sub-Feature Breakdown

### 3.1 F-SEC-01: Secure Boot

#### Description

Secure Boot ensures that only authenticated and authorized firmware images are executed on the Sensor Hub. During system startup, the bootloader verifies the cryptographic signature of the firmware image before handing over execution.

If verification fails, the system enters a defined **security fault state** and prevents normal operation.

#### Responsibilities

*   Firmware authenticity verification
    
*   Root-of-trust enforcement
    
*   Prevention of downgrade or rollback attacks (if enabled)
    

#### Constraints

*   Must complete before any application code execution
    
*   Must be enforced on every boot (cold or warm)
    

### 3.2 F-SEC-02: Secure Flash Storage

#### Description

Secure Flash Storage protects sensitive data stored in internal flash and external storage (e.g., SD card) from unauthorized access or modification.

Sensitive data includes:

*   Firmware images
    
*   Machine constants
    
*   Calibration data
    
*   Cryptographic material
    
*   Persistent diagnostics and logs
    

#### Responsibilities

*   Encrypted storage of sensitive regions
    
*   Access control enforcement
    
*   Prevention of unauthorized read/write operations
    

#### Constraints

*   Encryption must not compromise system boot reliability
    
*   Storage access must be mediated through controlled software components (e.g., DP component)
    

### 3.3 F-SEC-03: Encrypted Communication

#### Description

Encrypted Communication ensures that all data exchanged between the Sensor Hub and other entities (Main Hub, peer Sensor Hubs) is protected against eavesdropping, tampering, and impersonation.

This includes:

*   Sensor data transmission
    
*   Diagnostics reporting
    
*   OTA negotiation and data transfer
    
*   Configuration and machine constant updates
    

#### Responsibilities

*   Confidentiality of transmitted data
    
*   Integrity and authenticity verification
    
*   Secure session establishment
    

#### Constraints

*   Must be compatible with ESP32-S3 cryptographic capabilities
    
*   Must support reconnection and key renewal mechanisms
    

## 4 Functional Flow Overview

### Secure Boot Flow (Simplified)

```text
Power On
   ↓
ROM Bootloader
   ↓
Verify Firmware Signature
   ↓
[Valid] → Jump to Application
[Invalid] → Enter Security Fault State
```

### Secure Communication Flow (Simplified)

```text
Session Request
   ↓
Mutual Authentication
   ↓
Key Exchange
   ↓
Encrypted Data Exchange
```

## 5 System SHALL Requirements (Formal)

### Secure Boot Requirements

*   **SR-SEC-001**: The system shall verify the authenticity of the firmware image before execution during every boot cycle.
    
*   **SR-SEC-002**: The system shall prevent execution of firmware images that fail cryptographic verification.
    
*   **SR-SEC-003**: The system shall enter a defined security fault state upon secure boot failure.
    
*   **SR-SEC-004**: The system shall protect the root-of-trust against modification.
    

### Secure Flash Storage Requirements

*   **SR-SEC-005**: The system shall protect sensitive data stored in internal flash memory from unauthorized access.
    
*   **SR-SEC-006**: The system shall support encryption of sensitive data stored in external storage.
    
*   **SR-SEC-007**: The system shall restrict access to cryptographic keys to authorized system components only.
    
*   **SR-SEC-008**: The system shall ensure data integrity for stored configuration and machine constant files.
    

### Encrypted Communication Requirements

*   **SR-SEC-009**: The system shall encrypt all communication with the Main Hub.
    
*   **SR-SEC-010**: The system shall ensure integrity and authenticity of all received and transmitted messages.
    
*   **SR-SEC-011**: The system shall use secure communication channels for OTA firmware updates.
    
*   **SR-SEC-012**: The system shall detect and report communication security violations.
    

## 6 Traceability Matrix (Feature → System Requirements)

<figure class="table op-uc-figure_align-center op-uc-figure"><table class="op-uc-table"><thead class="op-uc-table--head"><tr class="op-uc-table--row"><th class="op-uc-table--cell op-uc-table--cell_head"><p class="op-uc-p">Feature ID</p></th><th class="op-uc-table--cell op-uc-table--cell_head"><p class="op-uc-p">Related System Requirements</p></th></tr></thead><tbody><tr class="op-uc-table--row"><td class="op-uc-table--cell"><p class="op-uc-p">F-SEC-01</p></td><td class="op-uc-table--cell"><p class="op-uc-p">SR-SEC-001, SR-SEC-002, SR-SEC-003, SR-SEC-004</p></td></tr><tr class="op-uc-table--row"><td class="op-uc-table--cell"><p class="op-uc-p">F-SEC-02</p></td><td class="op-uc-table--cell"><p class="op-uc-p">SR-SEC-005, SR-SEC-006, SR-SEC-007, SR-SEC-008</p></td></tr><tr class="op-uc-table--row"><td class="op-uc-table--cell"><p class="op-uc-p">F-SEC-03</p></td><td class="op-uc-table--cell"><p class="op-uc-p">SR-SEC-009, SR-SEC-010, SR-SEC-011, SR-SEC-012</p></td></tr></tbody></table></figure>

## 7 Design &amp; Implementation Notes (Non-Normative)

*   ESP32-S3 secure boot and flash encryption features should be leveraged where possible.
    
*   Key provisioning should occur during manufacturing or secure onboarding.
    
*   Security failures should integrate with the Diagnostics &amp; Health Monitoring feature set.
    
*   Security features must be active before any sensor data acquisition or communication begins.
    

## 8 Dependencies

*   **OTA Features** (for secure firmware updates)
    
*   **Communication Features** (transport layer)
    
*   **Diagnostics Features** (security fault reporting)
    
*   **Persistence &amp; DP Component** (secure storage abstraction)
    

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