Data Hiding in SIM/USIM Cards: A Steganographic Approach

The aim of this paper is twofold. First, the real structure of a SIM/USIM card file system will be presented, analyzing what is valuable from a forensics perspective and showing what evidence is not detectable and extractable with the tools present in the arena of open-source and proprietary software. After that, the paper will focus on a framework that can be used to detect and extract the so-called nonstandard part of a SIM/USIM file system, which is a concealed part usable also to store arbitrary and sensitive information. As a pro of-of-concept, an interesting example will be presented on the methods usable to obtain the data hiding in an ordinary SIM/USIM card