Devices are paired with a cell phone using Bluetooth to establish a unique and secure communication channel between the device and the phone. This helps insure the security of any data transmitted along the Bluetooth data link.
The Bluetooth wireless communications protocol is used to connect many devices to cell phones, including wireless headsets, computers and even other cell phones. The pairing process is part of the security mechanism of Bluetooth that prevents unauthorized devices from hijacking the communications channel established between the cell phone and the device. For example, a hacker using a computer to steal Internet access or data from a cell phone could impersonate a paired laptop that normally uses a Bluetooth connection for wireless Internet access easily if the cell phone accepted connections from any device. However, since Bluetooth only accepts connections from paired devices, it is much harder to do this. Pairing devices also helps eliminate the possibility of sending data to the wrong device, such as sending a conversation meant for one person's wireless Bluetooth headset to the headset of another person standing nearby.
Early Bluetooth pairing mechanisms used simple PIN number security schemes that were sometimes hard-coded into devices. These schemes had significant flaws, leading to the adoption of the Secure Simple Pairing method used in Bluetooth 2.1 and later versions. This method of pairing uses a public key cryptography algorithm similar to that used by the Secure Sockets Layer technology used on web sites.