Bridgefy, a popular messaging app for conversing with one another when internet connections are heavily congested or completely shut down, is a privacy disaster that can allow moderately-skilled hackers to take a host of nefarious actions against users, according to a paper published on Monday. The findings come after the company has for months touted the app as a safe and reliable way for activists to communicate in large gatherings. Ars Technica reports: By using Bluetooth and mesh network routing, Bridgefy lets users within a few hundred meters — and much further as long as there are intermediary nodes — to send and receive both direct and group texts with no reliance on the Internet at all. Bridgefy cofounder and CEO Jorge Rios has said he originally envisioned the app as a way for people to communicate in rural areas or other places where Internet connections were scarce. And with the past year’s upswell of large protests around the world — often in places with hostile or authoritarian governments — company representatives began telling journalists that the app’s use of end-to-end encryption (reiterated here, here, and here) protected activists against governments and counter protesters trying to intercept texts or shut down communications.
[R]esearchers said that the app’s design for use at concerts, sports events, or during natural disasters makes it woefully unsuitable for more threatening settings such as mass protests. They wrote: “Though it is advertised as ‘safe’ and ‘private’ and its creators claimed it was secured by end-to-end encryption, none of aforementioned use cases can be considered as taking place in adversarial environments such as situations of civil unrest where attempts to subvert the application’s security are not merely possible, but to be expected, and where such attacks can have harsh consequences for its users. Despite this, the Bridgefy developers advertise the app for such scenarios and media reports suggest the application is indeed relied upon.”
The researchers are: Martin R. Albrecht, Jorge Blasco, Rikke Bjerg Jensen, and Lenka Marekova from Royal Holloway, University of London. After reverse engineering the app, they devised a series of devastating attacks that allow hackers — in many cases with only modest resources and moderate skill levels — to take a host of nefarious actions against users. The attacks allow for: deanonymizing users; building social graphs of users’ interactions, both in real time and after the fact; decrypting and reading direct messages; impersonating users to anyone else on the network; completely shutting down the network; and performing active man-in-the-middle attacks, which allow an adversary not only to read messages, but to tamper with them as well. “The key shortcoming that makes many of these attacks possible is that Bridgefy offers no means of cryptographic authentication, which one person uses to prove she’s who she claims to be,” the report adds. “Instead, the app relies on a user ID that’s transmitted in plaintext to identify each person. Attackers can exploit this by sniffing the ID over the air and using it to spoof another user.”
The app also uses PKCS #1, an outdated way of encoding and formatting messages so that they can be encrypted with the RSA cryptographic algorithm. “This encoding method, which was deprecated in 1998, allows attackers to perform what’s known as a padding oracle attack to derive contents of an encrypted message,” reports Ars.