Bluetooth Security
- doc
- privacy
- attack
- nist sp 800-121
doc
Dialog SDK 5.0.x/6.0.x Tutorial Pairing, Bonding and Security
Understanding Bluetooth Security By Mark Loveless
Security Considerations For Bluetooth Smart Devices
Bluetooth’s Complexity Has Become a Security Risk
Breaking BLE — Vulnerabilities in pairing protocols leave Bluetooth devices open for attack
Evaluation of Out-of-Band Channels for IoT Security
privacy
Protecting Privacy of BLE Device Users
Bluetooth Low Energy - privacy enhancement for advertisement
Automatic Fingerprinting Of Vulnerable BLE IoT DevicesWith Static UUIDs From Mobile Apps
attack
CVE-2018-5383: Breaking the Bluetooth Pairing – The Fixed Coordinate Invalid Curve Attack
Bluetooth Impersonation Attacks (BIAS)
Misbinding Attacks on Secure Device Pairing and Bootstrapping
Breaking BLE — Vulnerabilities in pairing protocols leave Bluetooth devices open for attack
blesa
BLESA: Spoofing Attacks against Reconnections in Bluetooth Low Energy
缺乏authentication & encryption，伪造交互信息，从secure connection降级
其根源在于向后兼容，允许降级
misbinding attack
Misbinding Attacks on Secure Device Pairing and Bootstrapping
ble pairing & eap-noob 的核心问题在于，pairing时并未对device identifier做认证。因此存在identity misbinding的风险。
缓解：sts, sigma, ike
device provsioning protocol (dpp)
nist sp 800-121
NIST SP 800-121 Guide to BluetoothSecurity
RSSI: received signal strength indication 信号强度
data rate
BR: basic rate
EDR: Enhance data rate
AMP: Alternate MAC/PHYs, 即HS高速连接
LE: Low Energy
device mode
discoverable mode: 设备周期性的监测是否有inquiry
connectable mode: 设备周期性的扫瞄是否有可用连接
inquiry
paging
advertising
Device Architecture
Host: GAP, SMP, ATT/GATT, SDP, L2CAP…
LE Controller: Link Manager/Controller (LLP)
BR/EDR Controller: Link Controller (LCP), Link Manager(LMP)
L2CAP: Logical Link Control and Adaptation Protocol
SDP: Service Discovery Protocol
topo
BR/EDR: 7 active slave devices, 255 inactive slave devices
LE: unlimited number of slaves ——扯。。。
security
主要考察：pairing, link key generation, authentication, confidentiality 信息
注意，蓝牙支持是设备层认证，而非用户层认证
设备双方pairing成功后，存储相关的shared secret keys，后续进入Bonding模式，复用这些keys，无需重复pairing。
BR/EDR/HS的安全指标：FIPS alg， MITM protection，user interaction during pairing, encryption
如果要求Device满足FIPS要求，则除Service Discovery场景之外，设备应在Secure Connections Only模式。
pairing & link key generation
pairing的核心是经过authentication，设备双方获得对称密钥（即LK/LTK)
LE: Long Term Key (LTK)
BR/EDR: Link Key (LK)
PIN/legacy Pairing
Legacy low energy pairing: 协商生成TK，基于TK+random生成 STK (Short Term Key)，使用STK distribute Slave/Master LTK，也就是key transport
PIN Pairing: 基于PIN码派生Link Key——与secure connection不同。
Low Energy Pairing: 没有ECDH，无法防eavesdropping；能抓包就能破（除了OOB）。
secure simple pairing
Low Energy secure connection: ECDH协商生成LTK，key agreement；可以抵御eavesdropping
4种连接模式：
- Numeric Comparision（仅secure connection支持此模式）：用户查看两个互联的设备显示的6位digit是否一致；注意，digit仅参与认证，不参与密钥派生，digit无需保密——可以抵御eavesdropping；可以抵御MITM（用户确认）
- Passkey Entry: 用户查看一个设备显示的digit，在另一个设备输入6位digit；注意，digit仅参与认证，不参与密钥派生，digit无需保密——可以抵御eavesdropping；可以抵御MITM（用户输入）
- Just Works: 两个互联设备无显示、无输入，直接连接；底层处理与Numeric Comparision类似——无法抵御MITM
- Out of Band (OOB): 通过NFC之类的外围设备，交换连接信息——可抵御MITM、eavesdropping
AMP Link Key
AMP LK从Bluetooth Link Key派生，HMAC-SHA256
device authentication
challenge-response模式，基于link key的机密性保证，challenge由verifier随机生成，由claimant提供证明
legacy authentication
e1 alg，基于link key， bd_addr, rand计算出SRES(32 bit), ACO(06 bit)
SRES用于校验
ACO用于后续派生加密key
seucure authentication
基于双向bd_addr, rand，结合link key计算SRES
注意两个方向的SRES不同
Master ACO用于后续派生加密key
confidentiality
mode 1: no encryption
mode 2: individual link keys 加密配对数据；广播数据不加密
mode 3: 所有数据用master link key加密
加密key记为K_c，注意协商key size要有漏洞的
E0 Encryption alg
基于link key，结合COF值派生K_c
COF:
- Master Link Key的场景，取
Addr_M || Addr_S - Individual Link Key的场景，取ACO
AES-CCM encryption alg
link key, BD_ADDR, btak（固定字串），ACO 派生AES KEY
fips alg
BR/EDR : P-256, HMAC-SHA256
LE: P-256, AES-CMAC
AES-CCM
LK & LTK
BR/EDR的 link key 可以与 LE的Long Term Key 相互派生,
结合设备双方的addr & random做派生，h6 aes-cmac-128
IRK ( Identity Resolving Key )
LE隐私feature支持，IRK用于map Resolvable Private Address (RPA) to an Identity Address
Identity Address: 随机固定地址，或者公共地址
开启RPA更新，即，周期性更换基于IRK+随机hash处理的地址
CSRK
没加密的数据流，可以用CSRK做一下MAC校验
LE legacy pairing: LTK/IRK/CSRK key transport
LE Secure Connection: LTK key agreement, IRK/CSRK key transport
Vulnerabilities
MITM protection (Just Work)
ECDH KEY太弱
passkey的随机性
降级攻击
蓝牙地址关联到个人
Link Key安全存储
Device Discoverable
Mitigation
security vs cost, performance, operational
security equipment, inconvenience, maintenance, operation
defense-in-depth
user authorize
application-level authentication/encryption
PKI, two-factor
不要太经常pairing
