Expert Analysis Reveals Cryptographic Weaknesses in Threema Messaging App

guest · Jan 10, 2023

Threema comes with unusually strong claims. They crumble under new research findings.
By Ravie Lakshmanan - January 10, 2023

A comprehensive analysis of the cryptographic protocols used in the Swiss encrypted messaging application Threema has revealed a number of loopholes that could be exploited to break authentication protections and even recover users' private keys.
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The seven attacks span three different threat models, according to ETH Zurich researchers Kenneth G. Paterson, Matteo Scarlata, and Kien Tuong Truong, who reported the issues to Threema on October 3, 2022. The weaknesses have since been addressed as part of updates released by the company on November 29, 2022.

Threema is an encrypted messaging app that's used by more than 11 million users as of October 2022. "Security and privacy are deeply ingrained in Threema's DNA," the company claims on its website.
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While Threema has been subjected to third-party code audits at least twice – once in 2019 and a second time in 2020 – the latest findings show that they weren't thorough enough to uncover the problems present in the "cryptographic core of the application."

"Ideally, any application using novel cryptographic protocols should come with its own formal security analyses (in the form of security proofs) in order to provide strong security assurances," the researchers said.
In a nutshell, the attacks could pave the way for a wide range of exploitation scenarios, namely allowing an attacker to impersonate a client, reorder the sequence of messages exchanged between two parties, clone the account of a victim user, and even leverage the backup mechanism to recover the user's private key.
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Three Lessons from Threema - Analysis of a Secure Messenger

Threema is a Swiss encrypted messaging application. It has more than 10 million users and more than 7000 on-premise customers. Prominent users of Threema include the Swiss Government and the Swiss Army, as well as the current Chancellor of Germany, Olaf Scholz. Threema has been widely advertised as a secure alternative to other messengers.

In our work, we present seven attacks against the cryptographic protocols used by Threema, in three distinct threat models. All the attacks are accompanied by proof-of-concept implementations that demonstrate their feasibility in practice.
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Disclosure and Mitigations
We disclosed our findings to the Threema development team on the 3rd of October 2022, including possible mitigations for the attacks.

On the 29th of November 2022, Threema released a new protocol, Ibex, in order to further mitigate our attacks. The Ibex protocol aims to provide forward security for the E2E layer in Threema. We have not audited this new protocol.
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Paper (PDF): https://breakingthe3ma.app/files/Threema-PST22.pdf

guest · Jan 11, 2023

Threema disputes crypto flaws disclosure, prompts security flap
By John Leyden @jleyden - January 11, 2023

Security researchers have defended academics who discovered several serious security flaws in Threema following criticism of their work by developers of the encrypted messaging app.

A team of computer scientists from Swiss university ETH Zurich found a total of seven vulnerabilities in secure messaging app Threema, which boasts 10 million users including the Swiss Government and current Chancellor of Germany, Olaf Scholz.
The researchers disclosed this flaw and six other vulnerabilities to Threema’s developers in early October last year. Modifications were made before Threema released a new protocol, Ibex, to further mitigate the attacks in late November 2022.
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‘Hopelessly oversell’
Threema decided to then disrespect the researchers in responding to publication of their findings, earning the ire of the wider infosec community in the process.

“There’s a new paper on Threema’s old communication protocol,” the vendor wrote on its official Twitter account. “Apparently, today’s academia forces researchers and even students to hopelessly oversell their findings. Here’s some real talk.”
In an associated statement, Threema acknowledged that “while some of the findings presented in the paper may be interesting from a theoretical standpoint, none of them ever had any considerable real-world impact”.
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‘Condescending’
Swiss security researcher Christian Folini described Threema’s response as “condescending”.

“It’s not your job to judge the quality of security research. Your job is to get your act together, present us with the fixes, and leave the assessment to third parties,” Folini said on Twitter.
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Expert Analysis Reveals Cryptographic Weaknesses in Threema Messaging App

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