Forensics tool nabs data from Signal, Telegram, WhatsApp

'Retroscope' smartphone app can retrieve your last five screens


USENIX VID University researchers have developed a new method to help forensic investigators extract data information from memory.

The tool, dubbed Retroscope, recovered data from up to the previous 11 screens displayed from up to 15 apps, with an average of five screens pulled from each.

Apps included Signal, Skype, WeChat, Gmail, Facebook, WhatsApp, and Telegram running on a Samsung S4, LG G3, and HTC One.

It is a "new paradigm in smartphone forensics", according to the team of Brendan Saltaformaggio, Rohit Bhatia, Xiangyu Zhang, and Dongyan Xu of Purdue University, and Golden G. Richard III of the University of New Orleans.

"We feel without exaggeration that this technology really represents a new paradigm in smartphone forensics," Saltaformaggio says.

"It is very different from all the existing methodologies for analyzing both hard drives and volatile memories."

The lead author says he was "amazed" by the lack of in-memory app data protection reckoning that information should be "shredded" after it is displayed.

Writing over expired screens will impact smartphone performance however and the team did not find an easy way to counter their forensic data extraction methods.

The team's work builds extends early research which recovered the last screen displayed by an Android application.

Retroscope is described in the paper Screen after Previous Screens: Spatial-Temporal Recreation of Android App Displays from Memory Images [PDF] and in a proof-of-concept video as a tool for police to pull new information from smartphones that have not been locked or shut down.

Youtube Video

Here's some of the detail from the Usenix paper:

Retroscope is inspired by the observations that app-internal data on previous screens exists much longer in memory than the GUI data structures that 'package' them and each app is able to perform context-free redrawing of its screens upon command from the Android framework.

Based on these, RetroScope employs a novel interleaved re-execution engine to selectively reanimate an app’s screen redrawing functionality from within a memory image. Our evaluation shows that RetroScope is able to recover full temporally-ordered sets of screens (each with 3 to 11 screens) for a variety of popular apps on a number of different Android devices.

Police have methods for preserving machines that have been left on in a bid to capture decrypted information and data stored in memory.

Jailed Silk Road kingpin Ross Ulbricht was nabbed in a public library with his laptop still running, securing police additional crucial evidence. ®


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