- •Contents
- •Preface
- •1 Introduction
- •1.1 Bluetooth system basics
- •1.1.1 Background
- •1.1.2 Trade-offs
- •1.1.3 Bluetooth protocol stack
- •1.1.4 Physical layer
- •1.1.5 Baseband
- •1.1.6 Link manager protocol
- •1.1.7 Logical link control and adaptation protocol
- •1.1.8 Host control interface
- •1.1.9 Profiles
- •1.2 Bluetooth security basics
- •1.2.1 User scenarios
- •1.2.2 Notions and terminology
- •References
- •2.1 Key types
- •2.2 Pairing and user interaction
- •2.3 Authentication
- •2.4 Link privacy
- •2.4.1 Protect the link
- •2.4.2 Encryption algorithm
- •2.4.3 Mode of operation
- •2.4.4 Unicast and broadcast
- •2.5 Communication security policies
- •2.5.1 Security modes
- •2.5.2 Security policy management
- •References
- •3 Bluetooth Pairing and Key Management
- •3.1 Pairing in Bluetooth
- •3.2 HCI protocol
- •3.3 LM protocol
- •3.4 Baseband events
- •3.4.1 Initialization key generation
- •3.4.2 Unit key generation
- •3.4.3 Combination key generation
- •3.4.4 Authentication
- •3.4.5 Master key generation
- •3.5 User interaction
- •3.6 Cipher key generation
- •3.7 Key databases
- •3.7.1 Unit keys generation requirements
- •3.7.2 Combination key generation requirements
- •3.7.3 Key databases
- •3.7.4 Semipermanent keys for temporary use
- •References
- •4 Algorithms
- •4.1 Crypto algorithm selection
- •4.1.1 Block ciphers
- •4.1.2 Stream ciphers
- •4.2 SAFER+
- •4.3 Encryption engine
- •4.4 Ciphering algorithm E0
- •4.4.1 Initialization
- •4.5 Implementation aspects
- •References
- •5 Broadcast Encryption
- •5.1 Overview
- •5.2 Preparing for broadcast encryption
- •5.3 Switching to broadcast encryption
- •References
- •6 Security Policies and Access Control
- •6.1 Objectives
- •6.1.1 Trust relations
- •6.1.2 Security levels
- •6.1.3 Flexibility
- •6.1.4 Implementation considerations
- •6.2 Security manager architecture
- •6.2.1 Overview
- •6.2.2 Device trust level
- •6.2.3 Security level for services
- •6.2.4 Connection setup
- •6.2.5 Database contents and registration procedure
- •Reference
- •7 Attacks, Strengths, and Weaknesses
- •7.1 Eavesdropping
- •7.2 Impersonation
- •7.3 Pairing
- •7.4 Improper key storage
- •7.4.1 Disclosure of keys
- •7.4.2 Tampering with keys
- •7.4.3 Denial of service
- •7.5 Unit key
- •7.6 Location tracking
- •7.6.1 Bluetooth device address and location tracking
- •7.6.2 Five different types of location tracking attacks
- •7.7 Implementation flaws
- •References
- •8 Providing Anonymity
- •8.1 Overview of the anonymity mode
- •8.2 Address usage
- •8.3 Modes of operation
- •8.4 Inquiry and paging
- •8.4.1 Connectable mode
- •8.4.2 Private connectable mode
- •8.4.3 General connectable mode
- •8.5 Alias authentication
- •8.6 Pairing
- •8.7 Anonymity mode LMP commands
- •8.8 Pairing example
- •References
- •9 Key Management Extensions
- •9.1 Improved pairing
- •9.1.1 Requirements on an improved pairing protocol
- •9.1.2 Improved pairing protocol
- •9.1.3 Implementation aspects and complexity
- •9.2 Higher layer key exchange
- •9.2.2 Higher layer key exchange with EAP TLS
- •9.3 Autonomous trust delegation
- •9.3.1 Security group extension method
- •9.3.3 Group extension method versus public key method
- •References
- •10 Security for Bluetooth Applications
- •10.1 Headset
- •10.1.1 Headset security model
- •10.1.2 Pass-key and key management
- •10.1.3 Example
- •10.2 Network access
- •10.2.1 Common access keys
- •10.2.2 Security architecture
- •10.2.3 Network service subscription
- •10.2.4 Initial connection
- •10.2.5 Subsequent access to NAcPs
- •10.3 SIM access
- •10.3.1 The SIM access profile
- •10.3.2 Securing SIM access
- •References
- •Glossary
- •List of Acronyms and Abbreviations
- •About the Authors
- •Index
128 |
Bluetooth Security |
8.2.3Alias addresses, BD_ADDR_alias
Since it is not possible to identify other anonymous devices based on their BD_ADDR when they are operating in the anonymous mode, anonymous devices must make use of an alternative device identifier in the Bluetooth authentication procedure. Also, the authentication procedure must be slightly modified. The new procedure, alias authentication, will be described in more detail in Section 8.5. The alias authentication is based on the usage of alias addresses, BD_ADDR_alias. An alias address is used purely for authentication purposes. For simplicity, the BD_ADDR_alias can be chosen to 48 bits like any ordinary device address. All the bits should be chosen uniformly, independently, and at random. Hence, the address field cannot be divided into any meaningful subfields. The support and use of alias addresses and authentication are necessary for making authentication in the anonymity mode work.
8.3 Modes of operation
In order to distinguish devices operating in the anonymous mode from devices that are not anonymous, we define two different modes of operation:
1.Nonanonymous;
2.Anonymous.
A Bluetooth device can only operate in one of these modes at a time. Both modes are in principle fully backward compatible with devices not supporting these new modes. The latter, of course, with the exception that the new features introduced in the anonymous mode cannot be utilized with standard devices. One can say that for anonymous devices, Bluetooth devices not supporting the anonymous mode will look like devices that always operate in nonanonymous mode. Devices in anonymous mode shall regularly update the active device address, BD_ADDR (see Section 8.2). In addition, devices supporting the anonymous mode need to support alias authentication (see Section 8.5).
When a device is in nonanonymous mode, it uses the fixed device address in all its communications. Devices that want to prevent the location tracking attacks based on the BD_ADDR, CAC, DAC, or hopping sequence choose to operate in the anonymous mode. Location tracking is in the anonymous mode prevented by regularly updating the active device address, as it is the address that is visible on the wireless link.