Dutch researchers have developed an Android app for dissidents and crims-on-the-go, that can not only protect sensitive data behind encryption but make a phone appear as if it has nothing to hide.

The app was developed to pass the casual inspection a non-technical copper would give a device when looking for encrypted data that could hint at a need for deeper probes by forensics types or white hats.

Revolutionaries and drug dealers seeking anonymity need only dial a phone number or punch an invisible widget five times to open their secret stash within the DroidStealth app, according to student developer quartet Olivier Hokke, Alex Kolpa, Joris van den Oever and Alex Walterbos of Delft University of Technology.

"Since simply encrypting the data is not enough, our approach provides an added step of obfuscation that increases security of the data: DroidStealth hides itself," the group wrote in the paper A Self-Compiling Android Data Obfuscation Tool co-authored with supervisor Johan Pouwelse.

"Instead of actually calling the number, the application launches, requesting the pin code. Furthermore, DroidStealth fully intercepts the call, making sure the number never gets added to the call log.

Secret data would be encrypted using Facebook's Conceal API and could not be accessed from other apps or from its original location.

The application works on stock, non-rooted phones and can be renamed to appear as a benign app to "hide in plain sight" and bolster ease of access for users while still evading a cursory search.

It was distributed "nomadically" as an untrusted app rather than from the Google Play Store which would show up in a user's list of installed apps.

The authors identified some vulnerabilities including that malware could monitor for the encryption of files, and if a user's phone was taken while they had decrypted files for viewing.

They said black was chosen for the app's UI "in order to give users the feeling that they are indeed working in secret". ®