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1 software design/features/SF-SEC_Security_Safety.md
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1 software design/features/SF-SEC_Security_Safety.md
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# Software Feature Specification
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## SF-SEC: Security & Safety
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**Software Feature ID:** SF-SEC
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**Mapped System Feature:** F-SEC (Security & Safety Features)
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**Version:** 1.0
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**Date:** 2025-02-01
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## 1. Feature Overview
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The Security & Safety software feature implements comprehensive security mechanisms to protect the system against unauthorized access, malicious firmware, and data breaches. This feature provides the software implementation of secure boot, secure flash storage, encrypted communication, and security violation handling.
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### 1.1 Mapped System Features
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- **F-SEC-01**: Secure Boot
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- **F-SEC-02**: Secure Flash Storage
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- **F-SEC-03**: Encrypted Communication
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- **F-SEC-04**: Security Violation Handling
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## 2. Static View - Component Architecture
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```mermaid
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graph TB
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subgraph "Security Management Layer"
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SM[Security Manager]
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SVH[Security Violation Handler]
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KM[Key Manager]
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end
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subgraph "Boot Security"
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SB[Secure Boot Controller]
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BV[Boot Validator]
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ARB[Anti-Rollback Manager]
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end
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subgraph "Communication Security"
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TLS[TLS Manager]
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CA[Certificate Authority]
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CM[Crypto Manager]
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end
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subgraph "Storage Security"
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FE[Flash Encryption Manager]
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SE[Storage Encryption]
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AI[Access Inspector]
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end
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subgraph "Hardware Security"
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EFUSE[eFuse Manager]
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HSM[Hardware Security Module]
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RNG[Random Number Generator]
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end
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SM --> SB
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SM --> TLS
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SM --> FE
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SM --> SVH
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SB --> BV
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SB --> ARB
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TLS --> CA
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TLS --> CM
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FE --> SE
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FE --> AI
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KM --> EFUSE
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KM --> HSM
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CM --> RNG
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```
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### 2.1 Component Interfaces
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#### 2.1.1 Security Manager Interfaces
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**Provided Interfaces:**
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- `ISecurityManager`: Main security management interface
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- `ISecurityPolicy`: Security policy enforcement interface
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- `ISecurityStatus`: Security status monitoring interface
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**Required Interfaces:**
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- `ISecureBootController`: Secure boot interface
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- `ITLSManager`: TLS communication interface
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- `IFlashEncryptionManager`: Flash encryption interface
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- `IDiagnosticsManager`: Diagnostic reporting interface
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#### 2.1.2 Key Manager Interfaces
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**Provided Interfaces:**
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- `IKeyManager`: Cryptographic key management interface
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- `ICertificateManager`: Certificate management interface
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- `IKeyStorage`: Secure key storage interface
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**Required Interfaces:**
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- `IeFuseManager`: eFuse hardware interface
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- `IHardwareSecurityModule`: HSM interface
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- `IRandomNumberGenerator`: RNG interface
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## 3. Dynamic View - Security Sequences
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### 3.1 Secure Boot Sequence
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```mermaid
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sequenceDiagram
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participant PWR as Power On
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participant ROM as ROM Bootloader
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participant SB as Secure Boot Controller
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participant BV as Boot Validator
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participant ARB as Anti-Rollback Manager
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participant APP as Application
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participant DIAG as Diagnostics
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PWR->>ROM: System Reset
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ROM->>SB: initializeSecureBoot()
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SB->>BV: validateFirmwareSignature()
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BV->>BV: verifyRSA3072Signature()
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BV->>ARB: checkAntiRollback()
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ARB-->>BV: version_valid
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alt Signature and Version Valid
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BV-->>SB: validation_success
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SB->>APP: jumpToApplication()
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else Validation Failed
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BV-->>SB: validation_failed
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SB->>DIAG: reportSecurityViolation(BOOT_FAILURE)
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SB->>SB: enterBootFailureState()
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end
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```
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### 3.2 TLS Communication Establishment Sequence
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```mermaid
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sequenceDiagram
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participant APP as Application
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participant TLS as TLS Manager
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participant CA as Certificate Authority
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participant CM as Crypto Manager
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participant MH as Main Hub
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participant KM as Key Manager
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APP->>TLS: establishSecureConnection(main_hub_address)
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TLS->>KM: getDeviceCertificate()
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KM-->>TLS: device_certificate
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TLS->>MH: TLS_ClientHello + Certificate
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MH->>TLS: TLS_ServerHello + Certificate
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TLS->>CA: validateServerCertificate(server_cert)
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CA-->>TLS: certificate_valid
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TLS->>CM: generateSessionKeys()
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CM-->>TLS: session_keys
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alt Mutual Authentication Success
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TLS-->>APP: secure_connection_established
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else Authentication Failed
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TLS->>DIAG: reportSecurityViolation(AUTH_FAILURE)
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TLS-->>APP: connection_failed
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end
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```
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### 3.3 Flash Encryption Access Sequence
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```mermaid
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sequenceDiagram
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participant APP as Application Component
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participant FE as Flash Encryption Manager
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participant AI as Access Inspector
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participant SE as Storage Encryption
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participant FLASH as Flash Hardware
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participant DIAG as Diagnostics
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APP->>FE: readSecureData(address, size)
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FE->>AI: validateAccess(component_id, address)
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alt Access Authorized
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AI-->>FE: access_granted
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FE->>SE: decryptData(address, size)
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SE->>FLASH: readEncryptedData(address, size)
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FLASH-->>SE: encrypted_data
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SE->>SE: aes256Decrypt(encrypted_data)
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SE-->>FE: decrypted_data
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FE-->>APP: secure_data
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else Access Denied
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AI-->>FE: access_denied
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FE->>DIAG: reportSecurityViolation(UNAUTHORIZED_ACCESS)
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FE-->>APP: access_error
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end
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```
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## 4. Software Constraints
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### 4.1 Performance Constraints
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- **SWC-SEC-001**: Secure boot validation must complete within 5 seconds
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- **SWC-SEC-002**: TLS handshake must complete within 10 seconds
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- **SWC-SEC-003**: Flash encryption/decryption must not add >10% overhead
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### 4.2 Resource Constraints
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- **SWC-SEC-004**: Certificate storage limited to 2KB per certificate
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- **SWC-SEC-005**: Cryptographic key storage limited to eFuse capacity
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- **SWC-SEC-006**: TLS session memory limited to 16KB
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### 4.3 Security Constraints
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- **SWC-SEC-007**: All cryptographic keys must be hardware-protected
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- **SWC-SEC-008**: Private keys must never be accessible in plaintext
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- **SWC-SEC-009**: Security violations must trigger immediate protective actions
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### 4.4 Reliability Constraints
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- **SWC-SEC-010**: Security system must remain operational during system faults
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- **SWC-SEC-011**: Security violations must be logged persistently
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- **SWC-SEC-012**: Boot failure must not compromise security state
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## 5. Traceability Matrix - Software Requirements
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| Software Requirement ID | Feature Mapping | Component | Verification Method |
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|-------------------------|-----------------|-----------|-------------------|
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| SWR-SEC-001 | F-SEC-01 | Secure Boot Controller | Hardware Test |
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| SWR-SEC-002 | F-SEC-01 | Boot Validator | Security Test |
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| SWR-SEC-003 | F-SEC-01 | Security Manager | Unit Test |
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| SWR-SEC-004 | F-SEC-01 | Anti-Rollback Manager | Hardware Test |
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| SWR-SEC-005 | F-SEC-02 | Flash Encryption Manager | Hardware Test |
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| SWR-SEC-006 | F-SEC-02 | Storage Encryption | Unit Test |
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| SWR-SEC-007 | F-SEC-02 | Key Manager | Security Test |
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| SWR-SEC-008 | F-SEC-02 | Access Inspector | Unit Test |
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| SWR-SEC-009 | F-SEC-03 | TLS Manager | Integration Test |
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| SWR-SEC-010 | F-SEC-03 | TLS Manager | Security Test |
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| SWR-SEC-011 | F-SEC-03 | TLS Manager | Integration Test |
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| SWR-SEC-012 | F-SEC-03 | Security Violation Handler | Unit Test |
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| SWR-SEC-013 | F-SEC-04 | Security Violation Handler | Unit Test |
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| SWR-SEC-014 | F-SEC-04 | Anti-Rollback Manager | Hardware Test |
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| SWR-SEC-015 | F-SEC-04 | Key Manager | Security Test |
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## 6. Implementation Notes
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### 6.1 Secure Boot Implementation
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- **Secure Boot V2**: Hardware-enforced signature verification
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- **Signature Algorithm**: RSA-3072 or ECDSA-P256
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- **Root of Trust**: One-time programmable eFuse key
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- **Anti-Rollback**: eFuse-based version tracking
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- **Boot Failure State**: Secure state with diagnostic reporting only
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### 6.2 Flash Encryption Architecture
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- **Algorithm**: AES-256 hardware-accelerated encryption
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- **Mode**: Release mode for production deployment
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- **Key Derivation**: Hardware-based from eFuse
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- **Transparency**: Automatic encryption/decryption on flash access
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- **External Storage**: Optional AES-256 encryption for SD card
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### 6.3 TLS Communication Security
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- **Protocol**: TLS 1.2 with mutual authentication (mTLS)
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- **Device Identity**: Unique X.509 certificate per device
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- **Private Key Storage**: eFuse or encrypted flash
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- **Certificate Size**: Optimized <2KB for ESP32-S3
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- **Session Management**: Automatic reconnection and key renewal
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### 6.4 Key Management System
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- **Root Keys**: Stored in one-time programmable eFuse
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- **Device Keys**: Derived from root keys using hardware KDF
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- **Session Keys**: Generated using hardware RNG
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- **Key Rotation**: Supported for communication keys
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- **Key Backup**: Not supported for security reasons
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### 6.5 Security Violation Handling
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- **Detection Mechanisms**:
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- Secure boot signature failures
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- TLS authentication failures
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- Unauthorized flash access attempts
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- Certificate validation failures
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- Message tampering detection
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- **Response Actions**:
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- Immediate diagnostic event generation
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- Connection termination for communication violations
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- System state transition to secure mode
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- Persistent logging of security events
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### 6.6 Certificate Management
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- **Device Certificate**: Factory-provisioned unique identity
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- **CA Certificate**: Root certificate for server validation
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- **Certificate Chain**: Minimal chain to conserve resources
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- **Validation**: Full chain validation with CRL support
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- **Provisioning**: Secure factory or field provisioning process
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### 6.7 Hardware Security Features
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- **eFuse**: One-time programmable secure storage
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- **Hardware RNG**: True random number generation
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- **Crypto Accelerators**: AES, SHA, RSA hardware acceleration
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- **Secure Boot ROM**: Immutable boot validation code
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- **Flash Encryption**: Hardware-transparent encryption
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### 6.8 Error Handling and Recovery
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- **Boot Failures**: Enter secure diagnostic mode
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- **Authentication Failures**: Reject connections, log events
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- **Key Corruption**: Attempt recovery, escalate if failed
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- **Certificate Expiry**: Graceful degradation with alerts
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- **Security Violations**: Immediate protective response
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### 6.9 Compliance and Standards
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- **Secure Boot**: Industry standard for embedded systems
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- **AES-256**: FIPS 140-2 approved encryption
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- **TLS 1.2**: Industry standard secure communication
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- **X.509**: Standard certificate format (RFC 5280)
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- **RSA/ECDSA**: Standard digital signature algorithms
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