User's Manual

Table Of Contents

CATC MERLIN MOBILE 1.00 CHAPTER 5

User’s Manual Recording Bluetooth Traffic

DRAFT

5.8 Bluetooth Encryption

Bluetooth encryption is a multi-staged process that provides devices with secure, encrypted

communications. The process begins with a device prompting the user for a Personal

Identification Number (PIN). When the right PIN is entered, the slave begins an encryption

setup dialogue with the master. At the beginning of this dialogue, the slave and the master

agree on a link key. A link key is a 128-bit value that the two devices use for authentication.

When the slave and master agree on a link key, the slave then negotiates for the transfer of

the encryption key from the master device. The encryption key is used to encrypt and

decrypt messages. Once the encryption key is transferred, both devices use it to encrypt all

subsequent communications.

In order for Merlin Mobile to decode encrypted traffic, it needs the link key for each

master-slave connection for which encryption will be used. If you know the link key, you

can enter it into the Encryption Setup dialog. If you do not know it, you give Merlin Mobile

the PIN for a device and allow Merlin Mobile to discover the link key on its own. Once

Merlin Mobile has the link key, it can capture the rest of what it needs by listening to the

master and slave devices as they negotiate for the encryption key.

5.8.1 Encryption Setup

Use the Encryption Setup dialog to configure Merlin Mobile to decipher encrypted

Bluetooth traffic.

Note: In order for Merlin Mobile to obtain the encryption key and decode the encrypted traffic, recording

needs to be started before the slave device connects to the master device.

To define encryption parameters:

Step 1 Select Setup > Encryption Options from the menu bar or click the Encryption

Options button on the toolbar.

The Encryption Setup dialog will open.

Step 2 Click Add Slave Device.

The Slave Device Address combo box and PIN Code and Current Link Key

text boxes will be activated.

Step 3 Select or manually enter the slave device's BD_ADDR in the Slave Device

Address combo box.

Step 4 Select ASCII or Hex and enter the PIN for the slave device in the PIN Code

text box.

-OR-

Enter the 128-bit link key value in the Current Link Key text box. The link

must be entered as a 32-digit hexadecimal value.

Note: If the master and slave were previously connected, they may already agree on

the link key. In this case, you will need to provide Merlin Mobile with the link

key instead of the PIN.