Cryptanalysis of SIMON-32/64
A weird paper was posted on the Cryptology ePrint Archive (working link is via the Wayback Machine), claiming an attack against the NSA-designed cipher SIMON. You can read some commentary about it here. Basically, the authors claimed an attack so devastating that they would only publish a zero-knowledge proof of their attack. Which they didn’t. Nor did they publish anything else of interest, near as I can tell.
The paper has since been deleted from the ePrint Archive, which feels like the correct decision on someone’s part.