TheCodeBreakers
So he eschews the overt methods of
secret communications for the covert. He resorts to open codes, hollow
heels, invisible inks, microscopically small missives—the stegano-graphic
methods that conceal the very fact that a message is being sent. He seeks
to communicate unnoticed.
And to block this very attempt and root out the enemy within,
governments erect great filters at their mail and cable ports of entry to
prevent and detect these clandestine communications. These sieves,
which let innocent messages flow through, are the censorship
organizations.
Descended in a sense from the black chambers of the 1700s, they are
creatures of war in democracies and of tyranny in dictatorships.
Censorship first sprang up on a major scale in World War I, and the
lessons that Britain learned then she put to good use twenty years later
when
S, SCRAMBLERS, AND SPIES 275
she again filtered communications. Even before the United States
annaabi.ee 
