What is the iBeacon Bluetooth Profile

It seems to based on advertisement data, particularly the manufacturer data:

4C00 02 15 585CDE931B0142CC9A1325009BEDC65E 0000 0000 C5

<company identifier (2 bytes)> <type (1 byte)> <data length (1 byte)>
    <uuid (16 bytes)> <major (2 bytes)> <minor (2 bytes)> <RSSI @ 1m>

• Apple Company Identifier (Little Endian), 0x004c
• data type, 0x02 => iBeacon
• data length, 0x15 = 21
• uuid: 585CDE931B0142CC9A1325009BEDC65E
• major: 0000
• minor: 0000
• meaured power at 1 meter: 0xc5 = -59

I have this node.js script working on Linux with the sample AirLocate app example.

For an iBeacon with ProximityUUID E2C56DB5-DFFB-48D2-B060-D0F5A71096E0, major 0, minor 0, and calibrated Tx Power of -59 RSSI, the transmitted BLE advertisement packet looks like this:

d6 be 89 8e 40 24 05 a2 17 6e 3d 71 02 01 1a 1a ff 4c 00 02 15 e2 c5 6d b5 df fb 48 d2 b0 60 d0 f5 a7 10 96 e0 00 00 00 00 c5 52 ab 8d 38 a5

This packet can be broken down as follows:

d6 be 89 8e # Access address for advertising data (this is always the same fixed value)
40 # Advertising Channel PDU Header byte 0.  Contains: (type = 0), (tx add = 1), (rx add = 0)
24 # Advertising Channel PDU Header byte 1.  Contains:  (length = total bytes of the advertising payload + 6 bytes for the BLE mac address.)
05 a2 17 6e 3d 71 # Bluetooth Mac address (note this is a spoofed address)
02 01 1a 1a ff 4c 00 02 15 e2 c5 6d b5 df fb 48 d2 b0 60 d0 f5 a7 10 96 e0 00 00 00 00 c5 # Bluetooth advertisement
52 ab 8d 38 a5 # checksum

The key part of that packet is the Bluetooth Advertisement, which can be broken down like this:

02 # Number of bytes that follow in first AD structure
01 # Flags AD type
1A # Flags value 0x1A = 000011010  
   bit 0 (OFF) LE Limited Discoverable Mode
   bit 1 (ON) LE General Discoverable Mode
   bit 2 (OFF) BR/EDR Not Supported
   bit 3 (ON) Simultaneous LE and BR/EDR to Same Device Capable (controller)
   bit 4 (ON) Simultaneous LE and BR/EDR to Same Device Capable (Host)
1A # Number of bytes that follow in second (and last) AD structure
FF # Manufacturer specific data AD type
4C 00 # Company identifier code (0x004C == Apple)
02 # Byte 0 of iBeacon advertisement indicator
15 # Byte 1 of iBeacon advertisement indicator
e2 c5 6d b5 df fb 48 d2 b0 60 d0 f5 a7 10 96 e0 # iBeacon proximity uuid
00 00 # major 
00 00 # minor 
c5 # The 2's complement of the calibrated Tx Power

Any Bluetooth LE device that can be configured to send a specific advertisement can generate the above packet. I have configured a Linux computer using Bluez to send this advertisement, and iOS7 devices running Apple's AirLocate test code pick it up as an iBeacon with the fields specified above. See: Use BlueZ Stack As A Peripheral (Advertiser)

This blog has full details about the reverse engineering process.