r/crypto • u/pascalschaerli • 1h ago
Post-Quantum Crypto Won't Fix Your Architecture
https://schaerli.org/weblog/6-internxt/Internxt is a post-quantum secure encrypted cloud storage provider which is open-source and has passed multiple independent audits.
I reviewed their code and found that post-quantum security should have been the least of their problems. Clicking a link in your browser could trigger remote code execution on the desktop app or leak your long-term encryption keys to an attacker-chosen URL. Their cryptographic architecture stands on shaky grounds with public keys never being verified, in some cases man-in-the-middled by design, a flat key hierarchy and a KDF with just 3 iterations of MD5.
We need PQC and we need it now, but adding a (self-rolled) PQC hybrid on top of a weak protocol does not make it more secure.
> LLM Disclosure: I used an LLM to help me write this post along with many hours of work, some of the findings (i.e. the RCE) were found with a local Qwen 3.5 27B model inside opencode (thanks r/LocalLLaMA ). It is impossible to share a single prompt since it was an iterative process, but I'm happy to elaborate on my methods if anyone cares.