This program is an effort to support the Xiaomi LYWSD03MMC temperature and humidity sensor in ESPHome. It uses the passive method to scan for the periodically emitted ADV BLE packages and automatically decrypts the payload.
The ecryption keys have been obtained using the original Xiaomi Home Android app and Remote PCAP. The Wireshark packet dump contains the clear text key if the root certificate has been setup correctly. By default the MITM certificate is installed in the user certificate store and not trusted. Recent Androids will not allow to use it unless it has been copied to the system certificate store. With Android USB debugging enabled, open a root shell and move the certificate to the system store:
$ adb root
$ adb shell
# mount -o remount,rw /system
# mv /data/misc/user/0/cacerts-added/0595058e.0 /system/etc/security/cacerts/
# chown root.root /system/etc/security/cacerts/*
Now the packet dump can be collected with PCAP Remote, sshdump and Wireshark (tutorial). Here is the relevant part from the Wireshark packet dump:
packet: POST /app/device/bltbind
"data" = "{"did":"blt.3.129q4nasgeg00","token":"20c665a7ff82a5bfb5eefc36","props":[{"type":"prop","key":"bind_key","value":"dc06a798095b178767c0b74185275352"},{"type":"prop","key":"smac","value":"A4:C1:38:BF:54:5D"}]}"The bind_key needs to be inserted into ble.cpp in the relevant std::map (I am afraid there is no config file).
There is also a python script mitemp_standalone.py salvaged from the HomeAssistant sensor.mitemp_bt custom component, which does the same thing as the program provided here. The as received packet is saved as msg.bin, which serves as input for the C++ decryptor.
python resources/mitemp_standalone.py
make
./build/mitemp --file msg.bin --debugThis repository serves as the basis for supporting the device in ESPHome. Development of a xiaomi_lywsd03mmc sensor component has been initiated. The xiaomi_ble component needs to be extended with the payload decryption code given here. Additionally the configuration of the sensor needs to include the encryption key. Contributions are most welcome.