Decayfmt: A File Format That Corrupts Itself Upon Each Opening

Introduction to Decayfmt

Decayfmt is a novel file format that introduces intentional, progressive data corruption each time a file is accessed. This mechanism is featured in This Week in Rust #660 and applies to both image (.idcy<x>) and text (.tdcy<x>) files. The corruption is permanent and irreversible from the file itself, meaning each read further damages the stored data.

The Instability Parameter

The degree of corruption per open is controlled by an 'instability parameter' denoted by 'x', which is a positive integer embedded in the filename. A higher 'x' value results in more significant corruption with each opening. For instance, an image with x=3 degrades gracefully over many opens, while x=10 can render it nearly unusable after a single open and pure noise after three.

Text and Image Degradation

Both image and text files exhibit this decay. Images progressively lose visual integrity, while text files garble into readable-looking nonsense, as corruption only swaps in printable characters. This ensures that the corrupted text remains somewhat legible, albeit nonsensical, rather than becoming binary noise.

Purpose and Limitations

Decayfmt is described as a "social contract enforced by math," not a security tool. It is explicitly stated not to be encryption, DRM, or a secure deletion utility. While corruption is honest and unrecoverable from the file itself, anyone with a backup or a hex editor can bypass the intended decay. The format emphasizes that if the original is desired, a backup must be maintained, and if non-recovery is the goal, no backup should be made.

Installation

Users with a Rust toolchain can install decayfmt via `cargo install decayfmt`. Alternatively, binaries are available for download from the releases page and can be added to the system's PATH. On macOS, unsigned binaries may require a right-click 'Open' workaround due to Gatekeeper.