CIA declassifies state-of-the-art spying techniques from World War I

[Fansome]

An interesting, related book is "The American Black Chamber", by America's first "Spymaster".

April 19, 2011
CIA Declassifies WWI-Era Secret Documents
By THE ASSOCIATED PRESS

WASHINGTON (AP) — The CIA is declassifying secrets for writing with invisible ink and even opening sealed letters without detection: state-of-the-art spying techniques from World War I.

Six secret documents, made available on the CIA's website Tuesday, show how diplomats and generals of yesteryear got the drop on each other. There's a document written in French about the German's secret ink formula, showing that the French had cracked the German code.

CIA Director Leon Panetta says it's possible to reveal these secrets now because the old methods have been far outpaced by recent advances in the chemistry of secret ink and the lighting methods used to detect it.

Documents on secret writing fall under the CIA's authority to declassify. The agency said it declassified more than a million historical documents last year alone.