SHDC Protocol
Smart Home Device Communications Protocol
A secure communication system for low-power sensors and security hubs. SHDC supports encrypted unicast messages, broadcasts, and key management in closed, trusted networks with maximum compatibility for embedded devices.
Transport Layer
- Protocol: UDP (primary), TCP (fallback)
- Port: 56700 (official SHDC port)
- Packet Size: Max 512 bytes
- Network: IPv4/IPv6 supported
Security
- Encryption: AES-256-GCM
- Signatures: Ed25519
- Key Management: Automated rotation
- Authentication: Identity-based
Device Roles
- Sensor: Embedded nodes sending data
- Hub: Control node handling routing
- Discovery: Automatic network discovery
- Topology: Star network architecture
Key Features
End-to-End Security
All communications are encrypted with AES-256-GCM and signed with Ed25519 for authenticity and integrity.
Low Power Optimized
Designed for battery-powered sensors with minimal packet overhead and efficient protocol design.
Auto Discovery
Sensors automatically discover hubs on the network using secure broadcast discovery protocol.
Key Rotation
Automatic key rotation for session and broadcast keys ensures long-term security.
Broadcast Support
Efficient encrypted broadcast commands from hub to all sensors in the network.
Replay Protection
Timestamp-based replay protection with nonce validation prevents message replay attacks.
Protocol Architecture
Packet Structure
Implementation Example
Motion Detection Event
// Motion sensor reporting to hub
Header:
├─ Type: 0x01 (EVENT_REPORT)
├─ Sensor ID: 0xAABBCCDD
├─ Timestamp: 1721476800
└─ Nonce: 0xC7F1A2
Encrypted Payload (AES-256-GCM):
├─ Event Type: 0x01 (Motion Detected)
├─ Data Length: 0x04
├─ Sensor Data: Temperature (22.5°C)
└─ Battery Level: 85%
Signature: Ed25519(Header + Encrypted Payload)
Total Size: ~96 bytesHub Discovery Process
// Sensor broadcasts discovery request
Destination: 255.255.255.255:56700 (UDP Broadcast)
Header:
├─ Type: 0x00 (HUB_DISCOVERY_REQ)
├─ Sensor ID: 0x00000000 (unassigned)
├─ Timestamp: 1721476800
└─ Nonce: 0x1A2B3C
Payload:
├─ Public Key: [32 bytes Ed25519 public key]
└─ Device Info: "MotionSensor-v1.2"
// Hub responds with discovery response
Response: Unicast to sensor IP:port
├─ Hub Identity: 0x12345678
├─ Network Key ID: 0xABCD
└─ Configuration: Join instructionsDevice Join Handshake
// Step 1: Sensor sends join request
JOIN_REQUEST (0x02):
├─ Device Capabilities
├─ Requested Sensor ID
└─ Authentication Challenge
// Step 2: Hub validates and responds
JOIN_RESPONSE (0x03):
├─ Assigned Sensor ID: 0xAABBCCDD
├─ Session Key: [32 bytes AES key]
├─ Broadcast Key: [32 bytes for group messages]
├─ Key Rotation Schedule
└─ Network Configuration
// Device is now authenticated and readySecurity Considerations
Cryptographic Algorithms
- AES-256-GCM: Authenticated encryption for payloads
- Ed25519: Digital signatures for message authenticity
- X25519: Key agreement for session establishment
- HKDF: Key derivation for session keys
Key Management
- Device Keys: Ed25519 keypair per device
- Session Keys: Rotated every 24 hours
- Broadcast Keys: Rotated every 15 minutes
- Key Storage: Secure flash or TPM recommended
Attack Mitigation
- Replay Attacks: Timestamp + nonce validation
- MITM Attacks: Ed25519 signature verification
- Eavesdropping: End-to-end AES-256-GCM encryption
- Key Compromise: Regular key rotation
Resources & Downloads
📄 Specification Document
Complete protocol specification with detailed message formats and security considerations.
Download Markdown