Technical deep-dive into wMBus protocol and AES encryption in smart water meters. Learn how data is transmitted securely from Kamstrup meters to MeterSync platform.
Wireless M-Bus (wMBus) is the European standard for reading utility meters wirelessly. Combined with AES-128 encryption, it ensures secure transmission of consumption data from smart water meters. This technical guide explains how wMBus works and how MeterSync decrypts meter data in real-time.
Understanding wMBus Protocol
wMBus operates in the 868 MHz (Europe) or 169 MHz bands with variants for different use cases: Mode S (Stationary, one-way), Mode T (Frequent transmit, short range), Mode C (Compact, bidirectional). Kamstrup FlowIQ meters use Mode C1 with 16-second transmission intervals, achieving ranges up to 1000m in open areas.
wMBus Frame Structure
Each wMBus telegram contains: L-field (length), C-field (control), M-field (manufacturer ID), A-field (meter address), CI-field (control info), and the encrypted data payload. The manufacturer ID for Kamstrup is 'KAM' (0x2D2C). Understanding frame structure is essential for developing custom gateways and parsers.
AES-128 Encryption in Meters
Kamstrup meters use AES-128 CBC (Cipher Block Chaining) mode with a unique encryption key per meter. The 16-byte key is provided by Kamstrup during procurement. Without the correct key, meter data appears as random bytes. This prevents unauthorized reading and ensures only authorized systems can access consumption data.
MeterSync Decryption Process
MeterSync mobile app receives raw wMBus frames via BLE from our gateway or directly from BLE-enabled meters. The app extracts the encrypted payload, retrieves the meter's AES key from secure storage, and performs CBC decryption. The decrypted data includes volume (total and flow rate), water temperature, error codes, and timestamps.
Data Fields Decoded
After decryption, MeterSync parses: VIF (Value Information Field) identifying the data type, DIF (Data Information Field) specifying format and units, and the actual value. Kamstrup meters report volume in liters with 0.001L resolution, instantaneous flow in L/h, and various status flags for leak detection, reverse flow, and tamper alerts.
Integration Possibilities
MeterSync provides REST APIs for integrating decrypted meter data into third-party systems—billing software, building management systems, or custom dashboards. We also offer MQTT for real-time streaming to IoT platforms. Contact Greenify for API documentation and integration support.