Selected Publications

Recently, Apple removed access to various device hardware identifiers that were frequently misused by iOS third-party apps to track users. We are, therefore, now studying the extent to which users of smartphones can still be uniquely identified simply through their personalized device configurations. Using Apple’s iOS as an example, we show how a device fingerprint can be computed using 29 different configuration features. These features can be queried from arbitrary thirdparty apps via the official SDK. Experimental evaluations based on almost 13,000 fingerprints from approximately 8,000 different real-world devices show that (1) all fingerprints are unique and distinguishable; and (2) utilizing a supervised learning approach allows returning users or their devices to be recognized with a total accuracy of 97% over time.
In PoPETS Journal

Recent Publications

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  • Fingerprinting Mobile Devices Using Personalized Configurations

    Details PDF Code

  • Katz und Maus: iOS-Jailbreaks: Wie sich Entwickler gegen Angreifer behaupten können

    Details PDF

  • Schilde runter: iOS-Jailbreaks: Funktionsweise und Risiken

    Details PDF

  • DiOS: Dynamic Privacy Analysis of iOS Applications

    Details PDF Video Code Project

  • SNOOP-IT: Dynamische Analyse und Manipulation von Apple iOS Apps

    Details PDF Video Project

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or the False Sense of Security of Dropbox’s Passcode Protection Since the release of iOS 8, the Touch ID fingerprint sensor can now also be used in third-party apps. The Local Authentication framework provides an API via which users can conveniently deploy their biometric fingerprint to authenticate themselves in both apps from the App Store and enterprise apps. In the medium term, we anticipate that more and more apps will switch to the fingerprint method of user authentication.

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A comparison before and after iOS 8 was released As part of one of our recent research projects, we evaluated how malicious third-party apps could affect user privacy, despite the various security controls and the solid security architecture of the iOS platform. Therefore, we reviewed the iOS app sandbox model for weaknesses – and, indeed, made some finds. Some of these defects, which Markus Troßbach and I disclosed to Apple a while back, have been addressed with yesterday’s release of iOS 8 (CVE-2014-4361, CVE-2014-4362).

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A few weeks ago, I noticed that email attachments within the iOS 7 MobileMail.app are not protected by Apple’s data protection mechanisms. Clearly, this is contrary to Apple’s claims that data protection “provides an additional layer of protection for (..) email messages attachments”. I verified this issue by restoring an iPhone 4 (GSM) device to the most recent iOS versions (7.1 and 7.1.1) and setting up an IMAP email account1, which provided me with some test emails and attachments.

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