Cracking and hacking EncroChat

Speaker: Duncan Campbell, University of Sussex
Series: Computer Laboratory Security Seminar
Also open online: the joining details are on the talk's page.

EncroChat (2013-2020) was a third generation Criminally Dedicated Secure Communications (CDSC) service based on high cost customised and highly secured unsmart (or de-smarted) Android platforms using E2EE to provide messaging, VOIP calling and image exchange for closed user groups.

EncroChat service was terminated in June 2020 after a highly publicised three month long covert law enforcement attack leading to thousands of convictions and large currency and narcotic seizures. The nature of the attacked devices was not well understood due to platform hardening and obfuscation. The technical means used to attack and infect devices was not disclosed and was described as subject to French national security law. The technical source of computer evidence generated from the attack then used throughout Europe was and remains unexplained. This approach flouted standard computer forensic procedures, so generating multiple legal challenges.

The late Professor Ross Anderson was among leading experts providing analyses and hypotheses about possible methodology. His and other expert reports on EncroChat are soon to be available to be downloaded from the collaborative European Joint Defense Team website. Ross hypothesised that the EncroChat hack used a novel form of attack on the Signal Messenger Double Ratchet protocol utilising PRNG poisoning. A lab simulation was tested by a doctoral student.

Duncan has recently reported and will describe the methods found to have been used to break into EncroChat devices to exfiltrate user activity and content.

CDSC systems appear not to have been systematically studied or reported as a class, either in criminology or technology. Herath and Dadwa (Balancing End-to-End Encryption and Public Safety, RUSI, 2022) locate CDSC as a subclass of issues arising in ongoing policy debates about E2EE and privacy, noting "There are two broad types of E2EE services being used for criminal purposes: mainstream E2EE platforms; and criminally dedicated secure communications (CDSCs)". The former class, such as channels and nets within major E2EE platforms, have been studied here and elsewhere, e.g. Ricaldi et al (Telegram’s Cybercrime Economy, 2025).

The CDSC class has distinct financial and marketing features as well as technological aspects. The implied automatic presumption of criminality on the part of users and providers is legally problematic, but has been argued to be supported empirically. Unknown to the developers, aspects of some CDSC created high visibility to SIGINT and thus additional tension between intelligence and prosecutorial used of hacked information.

The form of the French cyberattack has been found to be more expedient than sophisticated, combining an unpatched CVE with publicly available tools and a standard government malware manager, and with apparent security costs including heavy and risky side channel activity. Issues yet to be resolved include whether attacks were also attempted or possible on the embedded ZRTP secure VOIP app, the finding of very high data loss in exfil end product, and the means used to sign malware updates by both the law enforcement and cyber-investigators hackers.

Duncan Campbell is an investigative journalist and computer forensic expert. He was the first and most cited computer forensic expert providing expert evidence for UK and some overseas EncroChat cases. He is a senior visiting research fellow at the University of Sussex Law School.