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IEICE TRANSACTIONS on Information

FCReducer: Locating Symmetric Cryptographic Functions on the Memory

Ryoya FURUKAWA, Ryoichi ISAWA, Masakatu MORII, Daisuke INOUE, Koji NAKAO

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Summary :

Malicious software (malware) poses various significant challenges. One is the need to retrieve plain-text messages transmitted between malware and herders through an encrypted network channel. Those messages (e.g., commands for malware) can be a useful hint to reveal their malicious activities. However, the retrieving is challenging even if the malware is executed on an analysis computer. To assist analysts in retrieving the plain-text from the memory, this paper presents FCReducer(Function Candidate Reducer), which provides a small candidate set of cryptographic functions called by malware. Given this set, an analyst checks candidates to locate cryptographic functions. If the decryption function is found, she then obtains its output as the plain-text. Although existing systems such as CipherXRay have been proposed to locate cryptographic functions, they heavily rely on fine-grained dynamic taint analysis (DTA). This makes them weak against under-tainting, which means failure of tracking data propagation. To overcome under-tainting, FCReducer conducts coarse-grained DTA and generates a typical data dependency graph of functions in which the root function accesses an encrypted message. This does not require fine-grained DTA. FCReducer then applies a community detection method such as InfoMap to the graph for detecting a community of functions that plays a role in decryption or encryption. The functions in this community are provided as candidates. With experiments using 12 samples including four malware specimens, we confirmed that FCReducer reduced, for example, 4830 functions called by Zeus malware to 0.87% as candidates. We also propose a heuristic to reduce candidates more greatly.

Publication
IEICE TRANSACTIONS on Information Vol.E101-D No.3 pp.685-697
Publication Date
2018/03/01
Publicized
2017/12/14
Online ISSN
1745-1361
DOI
10.1587/transinf.2017EDP7143
Type of Manuscript
PAPER
Category
Information Network

Authors

Ryoya FURUKAWA
  PwC Cyber Services LLC,Kobe University
Ryoichi ISAWA
  National Institute of Information and Communications Technology
Masakatu MORII
  Kobe University
Daisuke INOUE
  National Institute of Information and Communications Technology
Koji NAKAO
  National Institute of Information and Communications Technology

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