Reverse engineered bearer/bridge implementation of the CSRMesh BTLE protocol including all necessary cryptographic and packing routines required to send valid packets over a CSRMesh BTLE network. This particular implementation currently only supports the CSRMesh lighting API and has been succssfully tested with Feit HomeBrite smart LED bulbs. However, the implemtation of other CSRMesh APIs should be quite straightformard if needed. Currently this only implements the sending and recieving of packets on networks with only one bulb per network PIN since I originally developed this with a single bulb to test with. However, I now plan to expand support to multi bulb networks since I have recently acquired a 2nd bulb and can confirm that this code does NOT work as intended when there is 2 bulbs setup with the same PIN on a mesh network.

• Feit HomeBrite A19 Household, Model AOM800/827/LED/HBR with 1 bulb per network PIN in a given area

• Python 3.x
• Recent version of bluez (requires gatttool binary)
• pycrypto

csrmesh-cli [-h] --pin (4 digit pin) --dest (destination BT address) 
[--level LEVEL] [--red RED] [--green GREEN] [--blue BLUE]

All levels are represented using numbers from 0 (off) to 255 (maximum)

The 128 bit network key used in CSRMesh networks is derived by concatenating the ASCII representation of the PIN with a null byte and the string 'MCP', computing the SHA256 hash of the string, reversing the order of the bytes in the resulting hash, and taking the first 16 bytes as the key.

Packets sent to CSRMesh devices require authentication as well as encryption. All multibyte types are represented in little endian format. To form a valid packet, the sequence number, the constant 0x0080, and N null bytes where N is equal to the size of the payload to be sent are concatenated together and encrypted using the network key using AES-128 in ECB mode. The result of such encryption is then truncated to the length of the payload to be sent. The payload is XOR'ed with the result of the previous encryption to form the encrypted payload. Next, the message authentication code is computed using HMAC-SHA256 using the network key as the secret of the following data: 8 null bytes, sequence number, constant 0x80 and encrypted payload. The order of the bytes in the resulting hash are then reversed and the hash truncated to 8 bytes. Finally, the packet is formed by contatenating the sequence number, constant 0x80, encrypted payload, truncated HMAC, and the constant 0xff.

Packets are then sent via the Bluetooth LE GATT protocol. To send a packet, the data must be written to two write only handles, 0x0011 and 0x0014. The first 20 bytes of the packet are first written to handle 0x0011 and then the remainder of the packet is written to handle 0x0014.