What does bluetooth pairing do technically?
From the Bluetooth client example at http://people.csail.mit.edu/albert/bluez-intro/x502.html, it seems I can simply connect to a remote Bluetooth socket as long as I have the Bluetooth MAC address of the device. If I can simply connect to a remote Bluetooth device, I am wondering what exactly does Bluetooth pairing do. When is pairing really needed? Update: From How does Bluetooth pairing work?, it appears the final result of pairing is that an encryption key gets stored on both sides. I assume, when you open a remote socket connection, the call is intercepted by the local bluetooth daemon. In turn, the daemon encrypts the data and sends to the remote device. The daemon on the remote device decrypts the data and sends to the remote client application: Device1Client—>Device1Daemon—>Device2Daemon—>Device2Client Is this assumption correct?
1 Answer 1
Yes, your assumption is partially correct. Encryption is one of the uses of Passkey.
Bluetooth pairing is necessary whenever two Bluetooth devices connect to each other to share resources. A trusted relationship is established between the devices using a numerical password, commonly referred to as a passkey. Depending on how often one Bluetooth device connects to another, the user might opt to have the passkey saved for future connection attempts or prompt to enter the passkey each time the devices request communication with each other.
This is already explained on Stack Overflow please check- How does Bluetooth pairing work?
In the below answer, I will try to explain what is not mentioned in the above link or answers.
In Pairing process, when the initiating device sends a ‘Pairing Request” to the other device. The two devices then exchange I/O capabilities, authentication requirements, maximum link key size, and bonding requirements. Basically, all this phase consists of, is the two devices exchanging their capabilities and determining how they are going to go about setting up a secure connection. It is also important to note that all data being exchanged during this phase is unencrypted.
Now the question is why this Phase is needed? As mentioned- “two devices exchanging their capabilities.” The pairing should happen between compatible device there is no point in Pairing you Mouse with a Headphone as Mouse capabilities are different than Headphone.
One more use of Pairing is – “determining how they are going to go about setting up a secure connection.” Here the frequency hopping pattern is determined for two reasons-
Bluetooth uses 79 radio frequency channels in the band starting at 2402 MHz and continuing every 1 MHz. It is these frequency channels that Bluetooth technology is «hopping» over. The signal switches carrier channels rapidly, at a rate of 1600 hops per second, over a determined pattern of channels. The hopping pattern is determined well during the pairing process so that no other device will know in which band of the frequency the data is being transferred at an instance. Its rare case that frequency hopping pattern can be the same for a couple of devices communicating hence collision is avoided.
Note: If any third device is able to capture the passkey then it can replicate the whole communication pattern and capture the data being transferred. This is how the BT Sniffers work.
I am not able to cover all the details as per SIG specs. I hope the above answers give you a clearer picture of the need for the Pairing process. Feel free to point out, if you want me to explain any specific point in detail.
How does Bluetooth pairing work?
This seems to be inaccurate, so would anyone be able to either expand further or actually explain how/what is communicated to result in a successful pairing of the devices?
I was thinking of incorporating some of this research into a final year project (University), but would at least need to know the something of the Bluetooth programming pairing first.
Any help would be much appreciated in describing how these initial communications work.
I’ve heard of terms such as ‘parked mode’, and ‘passive mode’ within my research, but am yet to find any ‘useful’ information in the programming behind the design, (and hence I have asked this question). The likes of googling this type of topic is also quite difficult as it seems to bring up stuff like ‘how to turn your bluetooth on’ pages, and not the design of the programming behind it.
Your question is just so broad I find it difficult to answer. Do you want to know the RF level? The link control level? The higher level protocols? All? But I do have a recommendation for a pretty good book that covers all of these in great detail. It was published in 2002 so doesn’t cover Bluetooth Low Energy. But it does cover the fundamental BT operation from the RF level up. «Bluetooth Operation and Use» by Robert Morrow.
2 Answers 2
Bluetooth Secure Simple Pairing uses Elliptic Curve Diffie Hellman (ECDH) public key cryptography with approximately 95 bits of entropy using the FIPS approved P192 elliptic curve.
The following parameters are given:
- The prime modulus p, order r, base point x-coordinate Gx, base point y- coordinate Gy.
- The integers p and r are given in decimal form; bit strings and field elements are given in hex.
p = 6277101735386680763835789423207666416083908700390324961279 r = 6277101735386680763835789423176059013767194773182842284081 b = 64210519 e59c80e7 0fa7e9ab 72243049 feb8deec c146b9b1 Gx = 188da80e b03090f6 7cbf20eb 43a18800 f4ff0afd 82ff1012 Gy = 07192b95 ffc8da78 631011ed 6b24cdd5 73f977a1 1e794811 There are five phases of Secure Simple Pairing:
1. Public key exchange
Each device generates its own Elliptic Curve Diffie-Hellman (ECDH) public-private key pair.
2. Authentication Stage 1
1 of 3 protocol options is chosen by the connecting devices based on the IO capabilities of the two devices. These are:
3. Authentication Stage 2
Each device confirms that both devices have successfully completed the exchange as stipulated by which of protocol was chosen and used in the previous step.
4. Link key calculation
A link key is computed from the derived shared key and the publicly exchanged data. This is the numeric code shown to the user.
5. LMP Authentication and Encryption
The encryption keys are generated. The devices are successfully connected.
Further Reading:
- Bluetooth user Interface Flow Diagrams for Bluetooth Secure Simple Pairing Devices (PDF)
- Bluetooth Core Complete Specification v4.0 vol0 (ZIP/PDF)the core specification is 138 pages and to fully answer your question would take at least 20 so to fully answer your question you’ll need to read the references
A trusted relationship is established between the devices using a numerical password, commonly referred to as a passkey. Depending on how often one Bluetooth device connects to another, the user might opt to have the passkey saved for future connection attempts or prompt to enter the passkey each time the devices request communication with each other.
For two devices to have the ability to pair, they must share the same bluetooth profile. The following is from the official Bluetooth website:
Pairing devices
Not all Bluetooth enabled devices are designed to be paired. Logically, there’s no reason to connect a wireless mouse to a wireless headset. You should be able to pair a Bluetooth enabled headset to a Bluetooth enabled phone, or a Bluetooth enabled mouse to a Bluetooth enabled computer.
If you’re not sure whether the two devices you want to connect are designed to be paired with each other, make sure their Bluetooth profiles match.
How to programmatically pair a bluetooth device on Android
For my application I’m trying to programmatically pair a bluetooth device. I’m able to show the pairing dialog for the device I want to pair and I can enter a pincode. When I press «Pair» the dialog is removed and nothing happens. I only need to support devices with Android 2.0 and newer. Currently I am using the following code to start the pairing progress:
public void pairDevice(BluetoothDevice device)
i spent several days looking for a solution to this exact issue. it appears that google considers force-pairing to be a security issue, so the ACTION types you have listed here don’t actually exist. i found the class you reference here: developer.oesf.biz/em/developer/reference/cinnamon/android/… but it’s not in the official docs: developer.android.com/reference/android/bluetooth/…
Using reflection you can call the method createBond from the BluetoothDevice class. Solution: See this post: How to unpair or delete paired bluetooth device programmatically on android(stackoverflow.com/questions/9608140/…)? There is also a solution for unpair.
10 Answers 10
I managed to auto request a pairing procedure with keyboard featured devices through an app working as a service checking the presence of a specific kind of device and a modified version of the Settings app.
I have to say that I was working on a custom device running Android 4.0.3 without external controls (no back/Home/confirm buttons): pairing a controller on boot complete without any interaction until PIN request was mandatory.
First I created a service starting an activity on boot (with android.intent.action.BOOT_COMPLETED and android.permission.RECEIVE_BOOT_COMPLETED) that checks periodically the presence of a 1344 class device (a keyboard, the only way to input data on request) on the onReceive callback:
public void onReceive(Context context, Intent intent) . BluetoothDevice dev = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE); . if(dev.getBluetoothClass().getDeviceClass() == 1344)
Once filtered I choose the first keyboard available and then I pass the BT address to the Settings app:
Intent btSettingsIntent = new Intent(Settings.ACTION_BLUETOOTH_SETTINGS); btSettingsIntent.putExtra("btcontroller", dev.getAddress()); startActivityForResult(btSettingsIntent, 1); The tricky part was looking for the best position to call the pairing process. Using only the
intent.putExtra(BluetoothDevice.EXTRA_PAIRING_VARIANT, PAIRING_VARIANT_PIN); led me to a paring dialog that once closed left me with the device paired, but unusable.
Digging into the classes of com.Android.settings.Bluetooth I found my way through the
createDevicePreference(CachedBluetoothDevice cachedDevice) in the DeviceListPreferenceFragment.
From there I did compare my previously selected BT address with those available coming up and once successfully matched I call
I know, it’s tricky and requires access to the Android source code, but in a custom environment it works.
I hope this could be helpful.