Firmware Insider: Bluetooth Randomness is Mostly Random

Authors: 

Jörn Tillmanns and Jiska Classen, SEEMOO, TU Darmstadt; Felix Rohrbach, Cryptoplexity, TU Darmstadt; Matthias Hollick, SEEMOO, TU Darmstadt

Abstract: 

Bluetooth chips must include a Random Number Generator (RNG). This RNG is used internally within cryptographic primitives but also exposed to the operating system for chip-external applications. In general, it is a black box with security-critical authentication and encryption mechanisms depending on it. In this paper, we evaluate the quality of RNGs in various Broadcom and Cypress Bluetooth chips. We find that the RNG implementation significantly changed over the last decade. Moreover, most devices implement an insecure Pseudo-Random Number Generator (PRNG) fallback. Multiple popular devices, such as the Samsung Galaxy S8 and its variants as well as an iPhone, rely on the weak fallback due to missing a Hardware Random Number Generator (HRNG). We statistically evaluate the output of various HRNGs in chips used by hundreds of millions of devices. While the Broadcom and Cypress HRNGs pass advanced tests, it remains indistinguishable for users if a Bluetooth chip implements a secure RNG without an extensive analysis as in this paper. We describe our measurement methods and publish our tools to enable further public testing.

Open Access Media

USENIX is committed to Open Access to the research presented at our events. Papers and proceedings are freely available to everyone once the event begins. Any video, audio, and/or slides that are posted after the event are also free and open to everyone. Support USENIX and our commitment to Open Access.

This content is available to:

BibTeX
@inproceedings {257202,
author = {J{\"o}rn Tillmanns and Jiska Classen and Felix Rohrbach and Matthias Hollick},
title = {Firmware Insider: Bluetooth Randomness is Mostly Random},
booktitle = {14th {USENIX} Workshop on Offensive Technologies ({WOOT} 20)},
year = {2020},
url = {https://www.usenix.org/conference/woot20/presentation/tillmanns},
publisher = {{USENIX} Association},
month = aug,
}
Tillmanns PDF

Presentation Video