Résumé
Robust steganography is a technique of hiding secret messages in images so
that the message can be recovered after additional image processing. One of the
most popular processing operations is JPEG recompression. Unfortunately, most
of today's steganographic methods addressing this issue only provide a
probabilistic guarantee of recovering the secret and are consequently not
errorless. That is unacceptable since even a single unexpected change can make
the whole message unreadable if it is encrypted. We propose to create a robust
set of DCT coefficients by inspecting their behavior during recompression,
which requires access to the targeted JPEG compressor. This is done by dividing
the DCT coefficients into 64 non-overlapping lattices because one embedding
change can potentially affect many other coefficients from the same DCT block
during recompression. The robustness is then combined with standard
steganographic costs creating a lattice embedding scheme robust against JPEG
recompression. Through experiments, we show that the size of the robust set and
the scheme's security depends on the ordering of lattices during embedding. We
verify the validity of the proposed method with three typical JPEG compressors
and the {ıt Slack} instant messaging application. We benchmark its security
for various embedding payloads, three different ways of ordering the lattices,
and a range of Quality Factors. Finally, this method is errorless by
construction, meaning the embedded message will always be readable.