[rw]

Stegasuras is convincing work and the quality looks excellent.

I wrote a steganographic tool in this same spirit back in 2011, called Plainsight.

Back then, we didn't have deep learning, and the "Imagenet moment for NLP" had yet to arrive.

My Python code, with examples, is here: https://github.com/rw/plainsight

Unlike the OP, my Plainsight algorithm is 100% invertible by construction, and accepts binary input. (I verified the inversion process with "roundtrip fuzzing", a technique I still use today.)

Plainsight uses each bit of the input message to generate tokens. Bits are used to decide how to traverse a Huffman-style n-gram tree, weighted by frequency. This tree of n-grams is the model used in both the encoding and decoding steps. The drawbacks to my method are that the output 1) can be verbose and 2) does not convince a human that it's plausible, except for short messages.

Stegasuras has orders-of-magnitude better output, and seems to solve the problems I couldn't solve eight years ago. I would venture that their new result has as much to do with advances in language modeling, as it does with the particulars of their encoding and decoding algorithms.

I'll also note that I'm glad these researchers were able to use grant money to do this work. As a non-academic, I applied for an AI Grant to support me in upgrading Plainsight to use deep learning, but I was turned away at the time.

Finally, one of the ideas I picked up back then is that spam can be used to contain secret messages. Send enough gibberish to enough people, with your intended recipient included, and you'll look like a spammer--not a spy:

   $ wget https://spamassassin.apache.org/publiccorpus/20030228_spam.tar.bz2
   $ tar -jxvf 20030228_spam.tar.bz2
   $ cat spam/0* > spam-corpus.txt

   $ echo "The Magic Words are Squeamish Ossifrage" | plainsight -m encipher -f spam-corpus.txt > spam_ciphertext
   
   $ cat spam_ciphertext
   (8.11.6/8.11.6) 3 (Normal) Internet can send e-mails until to transfer 26 10 [127.0.0.1]
   also include address from the most logical, mail business for your Car have a many our
   portals ESMTP Thu, 29 1.0 this letter on internet, <a style=3D"color: 0px; text/plain;
   cellspacing=3D"0" how quoted-printable about receiving you would like width=3D"15%"
   width=3D"15%" border="0" width="511" Date: Tue, 27 Thu, 19 26 because
   [e-mail] for
   
   $ cat spam_ciphertext | plainsight -m decipher -f spam-corpus.txt
   Adding models:
   Model: spam-corpus.txt added in 2.57s (context == 2)
   input is "<stdin>", output is "<stdout>"   
   deciphering: 100% | 543.84  B/s | Time: 0:00:00
   
   The Magic Words are Squeamish Ossifrage