Looking for Research Assistants (doctoral or post-doc) at University of Paderborn

As I announced a few weeks ago, in 2016 I will be moving to the University of Paderborn to start a tenured professorship there. As part of this move, I am looking for a number of new Ph.D. students and also PostDocs. The positions come with full funding for a number of years. You can find more information about these positions here. As stated, please direct your applications to se-jobs.cs@upb.de

If you have a deep interest in software engineering, especially software security, the I am very much looking forward to your application!

CFP: Workshop on Empirical Research Methods in Information Security @ WWW2016

There is a growing use of empirical research methods to address cyber security challenges. This workshop aims to contribute to developing a common understanding of these methods and to set guidelines for using them for the different sub-disciplines including, but not limited to: security in software engineering, network security, security in social networks, and usable security. Researchers who work with these methods are encouraged to submit their work to the workshop and share their findings and experience. The submission deadline is January 4th, 2016. More information are available here.

Releasing our in-depth Security Analysis of TrueCrypt

Over the timeframe of about six months, together with other colleagues from Fraunhofer SIT, our group has performed a comprehensive security analysis of the encryption software TrueCrypt. The study was conducted for the German Federal Office for Information Security (BSI), who is releasing the report today on its website. (English version here.)

In June 2014, the open-source disk-encryption solution TrueCrypt was abandoned by its anonymous developers, while at the same time hinting the many users of the solution at potential vulnerabilities. On behalf of the BSI, we examined TrueCrypt for vulnerabilities, both conceptually and on the level of program code. As part of this task, we also considered and reviewed the results of previous security assessments.

On previously reported vulnerabilities in the driver component

Our general conclusion is that TrueCrypt is safer than previous examinations suggest. About a month ago, for instance, Google’s Project Zero had discovered two previously unknown vulnerabilities in TrueCrypt, one of them classified as critical. The error allows such malicious code that already has access to the running computer system to acquire expanded system rights. The vulnerability should be fixed, as privilege escalation opens the door for other attacks. But similar problems could arise with any kernel-level driver. Importantly, the problem found does not provide an attacker simplified access to encrypted data. To exploit the vulnerability, the attacker would have to have far-reaching access to the system anyway, for example, via a Trojan Horse or some other form of remote or direct access.

It does not seem apparent to many people that TrueCrypt is inherently not suitable to protect encrypted data against attackers who can repeatedly access the running system. This is because when a TrueCrypt volume is mounted its data is generally accessible through the file system, and with repeated access one can install key loggers etc. to get hold of the key material in many situations. Only when unmounted, and no key is kept in memory, can a TrueCrypt volume really be secure. In result, TrueCrypt provides good protection mostly when storing encrypted data offline. If keeping a backup stored offline on a hard drive, for example, or keeping encrypted data on a USB flash drive to be sent via a human carrier, then this can be considered relatively secure.

On buffer overflows reported by OCAP

The Open Crypto Audit Project (OCAP) has carefully examined TrueCrypt in the past. We have analyzed the report and also conducted a brief email exchange with the people behind OCAP. We examined closely a number of buffer overflows their study had revealed. Using the usage of static-analysis tools such as the KLEE virtual machine we were able to prove, though, that these buffer overflows cannot actually occur at runtime, and thus cannot possibly be exploited. It’s great to see that tools such as KLEE can nowadays cope with such practical problems – a manual analysis would have been too complicated since many complex path conditions needed to be considered.

Weak retrieval of random numbers

If you look more closely at our report you will see that we did find some weaknesses in the way TrueCrypt retrieves the random numbers it uses for encryption. With a lack of randomness, an attacker can theoretically guess your encryption key more easily. This problem only occurs in non-interactive mode, though, or when using certain access-control policies on Windows. In result, it is unlikely that this problem has actually affected users in he wild. The problem is that if volumes were created with a weak key then afterwards there is no way to tell. To be on the safe side it would therefore be advisable to re-encrypt volumes with a version of TrueCrypt in which this flaw has been fixed.


In conclusion, I would say that the TrueCrypt code base is probably alright for the most parts. The flaws we found were minor, and similar flaws can occur also in any other implementation of cryptographic functions. In that sense TrueCrypt seems not better or worse than its alternatives. Code quality could be improved, though, as there are some places that call for a refactoring and certainly for better documentation. But generally the software does what it was designed for.

Note that the original designers documented all along a threat model stating that TrueCrypt cannot actually properly protect data on a running system. This matches our findings. If such protection is desired, one cannot get around solutions that use smartcards or other hardware-based key storage such that the encryption key can be better kept a secret. Also such systems can be broken, but they raise the bar significantly.

We hope that folks find our report useful. Thanks to everyone who supported our study, in particular to the BSI for funding it! We hope to be able to conduct further similar analyses in the future.

Update: First press coverage

Ars Technica: TrueCrypt is safer than previously reported, detailed analysis concludes
Threatpost: German Government Audits TrueCrypt
Digital Trends: Why TrueCrypt might not be so insecure after all

ZDNet: Fraunhofer-Institut: TrueCrypt ist „nur in sehr seltenen Fällen angreifbar“
MacLife: Truecrypt-Verschlüsselungssoftware sicherer als erwartet


To be presented at Black Hat Europe next week:

Smartphone applications frequently need to store data remotely. From a developer’s point of view, setting up and maintaining back-ends, however, is time-consuming and error-prone. Therefore, commercial cloud-based data storage solutions from Backend-As-A-Service (BaaS) providers such as the ones from Amazon, Google, and Facebook have become omnipresent. They provide simple APIs for common tasks such as managing database records or files. Adding a few library classes and writing three or four lines of code is sufficient to make an interaction between the cloud and the app, and, e.g., store credit card data. While this model is convenient, one might wonder whether it’s really secure in practice (spoiler: it’s not).
In this study, we will show that many BaaS solutions are completely insecure and attackers have no difficulties in breaking into the developer’s backend. We investigated about two million Android apps and the results were quite shocking. We were able to access more than 56 million sensitive user records stored in the cloud by heavily misconfigured BaaS solutions. These records contained all sorts of sensitive data processed by Android apps: medical information, credit card data, photos, voice-, audio- and video-records, money transaction records, etc. Some apps even contained credentials that gave us full control over the remote storage. Adversaries could hijack Amazon S3-Buckets which gives them the ability to modify sensitive customer databases, add malicious code to well-known websites or directly run malware on the cloud at the app developer’s expense. In order to find and verify these insecure BaaS solutions in Android applications, we developed an automatic exploit generator that extracts credentials from the app, even if they are obfuscated, and provides access to the respective BaaS backend.