Technical reports / Department Informatik
- Linux Memory Forensics: Dissecting the User Space Process Heap (2017)
- The analysis of memory during a forensic investigation is often an important step to reconstruct events. While prior work in this field has mostly concentrated on information residing in the kernel space (process lists, network connections, and so on) and in particular on the Microsoft Windows operating system, this work focuses on Linux user space processes as they might also contain valuable information for an investigation. Because a lot of process data is located in the heap, this work in the first place concentrates on the analysis of Glibc's heap implementation and on how and where heap related information is stored in the virtual memory of Linux processes that use the Glibc heap implementation. Up to now, the heap was mostly considered a large cohesive memory region from a memory forensics perspective, making it rather hard manual work to identify relevant information inside. We introduce a Python class for the memory analysis framework Rekall that is based on our analysis results and allows access to all chunks contained in the heap and their meta information. Further, based on this class, six plugins have been developed that support an investigator in analyzing user space processes: Four of these plugins provide generic analysis capabilities such as finding information/references within chunks and dumping chunks into separate files for further investigation. These plugins have been used to reverse engineer data structures within the heap for user space processes, while illustrating how such plugins ease the whole analysis process. The remaining two plugins are a result of these user space process analyses and are extracting the command history for the zsh shell and password entry information for the password manager KeePassX.
- Information Leakage behind the Curtain: Abusing Anti-EMI Features for Covert Communication (2016)
- We present a new class of covert channels which can be created by utilizing common hardware but that cannot be detected by such. Our idea is to abuse anti-EMI features of a processor to create a covert channel on the physical layer. Thus, the sender uses the invariants in how digital signals are encoded over analog channels to covertly transport information. This leaked data is present on the wire bound connections of the compromised device, but is also by definition present in the vicinity of the device and can be picked up by radio equipment. As the covert channel is present only on the physical layer, the data on all layers above, as well as the timing behavior on those layers is indistinguishable from uncompromised devices. We present two example implementations of such channels using RS-232 as the carrier and use a common oscilloscope to decode the resulting covert channel. Using this setup, we observed symbol rates of around 5 baud. We derive the theoretical upper bound of the covert channels bandwidth and discuss the factors by which it is influenced.
- Privacy-Preserving Email Forensics (2015)
- In many digital forensic investigations, email data needs to be analyzed. However, this poses a threat to the privacy of the individual whose emails are being examined and in particular becomes a problem if the investigation clashes with privacy laws. This is commonly addressed by allowing the investigator to run keyword searches and to reveal only those emails that contain at least some of the keywords. While this could be realized with standard cryptographic techniques, further requirements are present that call for novel solutions: (i) for investigation-tactical reasons the investigator should be able to keep the search terms secret and (ii) for efficiency reasons no regular interaction should be required between the investigator and the data owner. We close this gap by introducing a novel cryptographic scheme that allows to encrypt entire email boxes before handing them over for investigation. The key feature is that the investigator can non-interactively run keyword searches on the encrypted data and decrypt those emails (and only those) for which a configurable number of matches occurred. Our implementation as a plug-in for a standard forensic framework confirms the practical applicability of the approach.
- From Computer Forensics to Forensic Computing: Investigators Investigate, Scientists Associate (2014)
- This paper draws a comparison of fundamental theories in traditional forensic science and the state of the art in current computer forensics, thereby identifying a certain disproportion between the perception of central aspects in common theory and the digital forensics reality. We propose a separation of what is currently demanded of practitioners in digital forensics into a rigorous scientific part on the one hand, and a more general methodology of searching and seizing digital evidence and conducting digital investigations on the other. We thereby mark out the route for computer forensics to turn into a true forensic science. To illustrate the feasibility of the proposed path, we supply a couple of practical examples, as well as a list of exemplary questions that should be answered by digital forensic scientists.
- Analyse und Vergleich von BckR2D2-I und II (2011)
- Im Oktober 2011 erregte die Ver"offentlichung von Details über die inzwischen meist als BckR2D2 bezeichnete Schadsoftware öffentliches Aufsehen. Mitglieder des Chaos Computer Club e.V. veröffentlichten einen ersten Bericht über die Funktionsweise des Trojaners, dem weitere Analysen folgten. In dieser Arbeit geben wir einen Überblick über die bislang veröffentlichen Einzelberichte und über die verschiedenen Komponenten der Schadsoftware sowie deren Funktionsweise. Hierzu präsentiert diese Arbeit die wesentlichen Ergebnisse einer ausführlichen Analyse aller Komponenten des Trojaners und geht insbesondere auf Unterschiede zwischen den beiden bislang bekannten Varianten BckR2D2-I und II ein. Ziel dieser Arbeit ist auch die kritische Überprüfung der von anderen Autoren getroffenen Aussagen über die Schadsoftware.