The classic work on the history of crypto also contains a fair bit of material on
stego. This includes a classical Chinese practice of embedding the code ideogram at a
prearranged place in a dispatch; the warning the Greeks received of Xerxes' intentions
via writing underneath the wax of a writing tablet; various open and jargon codes;
the trick of dotting successive letters in a covertext with secret ink, due to Aeneas the
Tactician; Bacon's system of encoding using two slightly different typefaces; Madame
Defarge's knitting, which contained the names of enemies of the French Republic; the
Cardano grill, which picks out a subset of the words on a page as being significant;
and of course the whole technology of secret inks, microdots and the rest. The word
'steganography' was coined in 1499 by Trithemius, who encoded letters as religious
words in such a way as to turn covert messages into apparently meaningful prayers.
People interested in policy aspects will be interested to read of the restrictions imposed
by the USA in world war 2 to try and plug up as many channels as possible. The
post banned a large class of objects, including chess games, crosswords, and newspaper
clippings; lovers' X's were deleted; watch hands were shifted; orders for flowers could
not specify either the kind of flower or the date of delivery; and items such as loose
stamps and blank paper were replaced. Thousands of people were involved in reading
mail, looking for language which appeared to be forced. They also rephrased telegrams;
in one case, a censor changed 'father is dead' to 'father is deceased', which elicited the
reply 'is father dead or deceased?'
042100 `Rechnergestützte Steganographie: Wie sie Funktioniert und warum folglich jede Reglementierung von Verschlüsselung unsinnig ist'