Friday, December 19, 2014

Study Group: Efficient Smart Phone Forensics Based on Relevance Feedback

This week's study group was given by Panos on the subject of Efficient Smart Phone Forensics Based on Relevance Feedback[1].  

 The Digital Forensics Procedure has 4 major steps: Device Secure, Data Extraction, Data Analysis and Data Representation. To improve the efficiency of data analysis, a sub procedure known as forensic triage is involved to mark out the most relative information among in the phone. In this paper, a ranking system called LIFTR was presented to prioritize the information recovered from Android phones where the amounts of data are huge comparing to feature phones.

LIFTR is designed under following assumptions:
  1. Physical image of phone is acquired.
  2. The data is not encrypted. They are filtered binary files (which are the output of previous procedure).
  3. The format of data are list of strings, e.g. the result of DEC0DE or strings command.
LIFTR then takes the information parsed by recovery engine as the input alongside with optional suspect information, and then outputs a ranked list of the most important NAND pages.

There are two major steps in the design of LIFTR:
  1. Initial Ranking. The input of LIFTR are unranked pages. The initial ranking will mark the pages based on a relevance metric. After this procedure, the pages will be ranked for the next step.
  2. Relevance Feedback. After the initial ranking, LIFTR will present some possibly relevant fields of pages to the investigator and ask for the labelling, which is usually manually, of true and false positive. LIFTR then resorts the ranking by the labelling information assigning relevant pages with higher ranks and irrelevant pages lower. This process can be repeated multiple time to reach a better performance.

The experimental result shows that LIFTR can efficiently mark out the relevant pages. However, it does not guarantee the target information will be included in its result; therefore all data should still be analyzed during an investigation. However, LIFTR is still an effective tool to improve the efficiency of the investigation.

[1]Saksham Varma, Robert J. Walls, Brian Lynn, and Brian Neil Levine. 2014. Efficient Smart Phone Forensics Based on Relevance Feedback. InProceedings of the 4th ACM Workshop on Security and Privacy in Smartphones & Mobile Devices (SPSM '14). ACM, New York, NY, USA, 81-91. DOI=10.1145/2666620.2666628

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