Schneier on Security

Clive Robinson • February 13, 2025 6:37 AM

@ Bruce, ALL

Another AI and crypto project.

Apparently, “Textcoder is a proof-of-concept tool for steganographically encoding secret messages such that they appear as ordinary, unrelated text.”

(Which is something I’ve talked about off and on on this blog for a number of years, including the past few days using “Perfect Secrecy” encryption and a Code Book of phrases. So people can look back if they want the “basic and secure” idea).

This time however the system rather than use a traditional “code book” of phrases or words, the project,

https://github.com/shawnz/textcoder

Uses a current AI LLM system to get “Statistical weighting”.

To quote the project page,

“It works by taking the secret message, encrypting it to produce a pseudorandom bit stream, and then using arithmetic coding to decompress that bit stream based on a statistical model derived from an LLM. This produces text which appears to be sampled randomly from the LLM, while actually encoding the secret message in the specific token choices.”

So using the LLM as a digital filter to get a statistical set of phrases…

Some might remember a simple “coding” technique that made a statistical adjustment to letter frequency to help thwart manual cryptanalysis called a “Straddling Checkerboard”,

https://en.m.wikipedia.org/wiki/Straddling_checkerboard

That originated in the modern form around that “flattens the statistics” around about the late 1930’s. And later became used in the VIC cipher, that outside of “Perfect Secrecy” systems such as the “One Time Pad”(OTP) is the only known “pencil and paper” cipher to defeat the early days of the current US and UK SigInt agencies.