Just been reading "Garbo - the spy who saved D-day", which is an MI5 account released by the UK public records office of the Garbo case (the Germans thought Garbo, a Spaniard real name Juan Pujol, ran a ring of spies in Britain and was one of their best agents - in fact Garbo was a double agent, and there were no spies, just a lot of MI5 officers).
They communicated largely by using secret inks in letters to Spain/Portugal, and the book gives some tales of inks and developers, "striping", which is a technique whereby the censor applies a stripe of reagent to test for invisible inks - but the striping can be detected from examining innocent mail, so you use better secret inks - or you stripe with ineffective developers - and so on, in a maze of deception and double-cross. The interesting thing is that, even though the report, written in 1945, has now been released, the only things redacted (so far - I'm half way through) are the names of the inks and developers... -- Peter Fairbrother --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]