In 2019, researchers at TU Darmstadt discovered a . In 2021, the teams of computer science professors Matthias Hollick and Thomas Schneider jointly published a security vulnerability in Apple's offline file sharing system AirDropto fix the problem, but Apple failed to act. Now, a Chinese judicial authority has declared that it has spied on AirDrop users. privacy-friendly protocol (“PrivateDrop”)
AirDrop is a proprietary feature of Apple devices that allows users to share files wirelessly and offline with nearby iPhones, iPads or MacBooks. Once the data transfer is complete, there should be no way to determine where the data came from. The function therefore became attractive for political activists in China to share content critical of the government. However, this is risky due to critical privacy vulnerabilities in AirDrop.
With AirDrop, Apple stores so-called hashes in the system of the devices used to recognise whether the person with whom data should be exchanged is a known contact. However, security experts are well aware that cryptographic hash functions are not sufficient to protect personal data such as phone numbers or e-mail addresses, because today's computing power allows many possible solutions to be tried out quickly.
According to , Chinese authorities are said to have identified the telephone numbers and email addresses of individuals who sent information critical of the government which was distributed via AirDrop. Protocols on the recipients' devices were analysed and techniques were used to decrypt cryptographic procedures that are supposed to protect the senders' contact details. recent news reports
Disclosed but never closed
For the research teams of and CROSSING-PI Prof. Matthias Hollick from the Department of Computer Science at TU Darmstadt, the exploitation of the vulnerability comes as no surprise: the Prof. Thomas Schneider had already found serious security vulnerabilities in the AirDrop protocol in 2019 and reported them to Apple before publication at USENIX Security 2019 so that the company could have taken countermeasures (“Responsible Disclosure”). Together with researchers from the Secure Mobile Networking Lab (SEEMOO), they presented a demonstrator at WiSec 2021 how to practically exploit the vulnerability. Both teams published at USENIX Security 2021 a privacy-preserving solution called PrivateDrop. Cryptography and Privacy Engineering Group (ENCRYPTO)
uses an alternative, provably secure cryptographic protocol to determine whether two users know each other. In this way, log messages, even if they are intercepted or stored in a device log, become unusable for forensics. The new procedure allows contact data to be exchanged via AirDrop without the user having to reveal anything about themselves or their contact details. The researchers demonstrated that their method can be implemented without any noticeable delay in performance. PrivateDrop
In an exchange with Apple, it was announced to the researchers that the vulnerability would be closed with the introduction of their mobile operating system iOS 16 in 2022. A plan that has not yet been realised. The researchers now hope that Apple will take the reports as an opportunity to address the problem.
Affiliated Scientific Publications
PrivateDrop: Practical Privacy-Preserving Authentication for Apple AirDrop
by Alexander Heinrich, Matthias Hollick, Thomas Schneider, Milan Stute, and Christian Weinert in 30th USENIX Security Symposium (USENIX Security’21). Implementation available on GitHub.
Demo: AirCollect: Efficiently Recovering Hashed Phone Numbers Leaked via Apple AirDrop
by Alexander Heinrich, Matthias Hollick, Thomas Schneider, Milan Stute, and Christian Weinert in 14th ACM Conference on Security and Privacy in Wireless and Mobile Networks (WiSec’21) Demo Track.
A Billion Open Interfaces for Eve and Mallory: MitM, DoS, and Tracking Attacks on iOS and macOS Through Apple Wireless Direct Link
by Milan Stute, Sashank Narain, Alex Mariotto, Alexander Heinrich, David Kreitschmann, Guevara Noubir, and Matthias Hollick in 28th USENIX Security Symposium (USENIX Security’19).