ACROSTIC - Concealing a message within text using recurring features, i.e. every first letter of words. An example follows:
The hope is simple. If some Americans need education, xenophobia and matters pertaining lack equal opportunity for analysis now and current rules of society? they indicate consistency.
While making little or no sense, by reading the first letter of each word you have an example of an Acrostic message. Such messages are unlikely to be employed professionally, although they become harder to intercept if, say every fifth letter is used.
STEGANOGRAPHY- The practice of hiding an image, message, audio or video file within another.
INVISIBLE INK - Using invisible ink a message can be written on paper that is then concealed with a visible 'cover' message. Basic examples include lemon juice for ink, the message revealed by holding the paper over a heat source. More sophisticated 'wet systems' included dehydrated inks concealed as pharmaceutical tablets, chalk etc. When reconstituted, these would be used to write a letter on a plain page of paper. Before use, the paper was rubbed in all directions with a soft cloth, then placed on a sheet of glass (to reduce indentations). After the ink dried, the rubbing would be duplicated (to remove any remnant of message visible in the fibres of the paper) and a cover message written in ordinary ink.
DRY SYSTEMS - Using a variation of the carbon paper system, paper was impregnated with special chemicals and disguised as a blank page in a book. Sandwiched between two pieces of bond paper, the special paper would be placed on glass and the message written on the top paper. The 'carbon' paper would transfer the message invisibly to the bottom sheet.
Another advance was discovered by accident; Pentel Rollerball pens were found to be perfect for a similiar technique, the messages being developed by a special chemical solution, which could be disguised as after-shave or perfume.
MICRODOTS - Photographically reduced image of a page of text to a size less than 1mm square. Microdots required viewers capable of x100 magnification. Time consuming to produce and difficult to use, even for trained agents knowing where to look. Current laser engraving systems enable mesages to be concealed in even smaller areas on commercially-printed materials and magazines.
ABOVE: CIA microdot camera circa 1965
BELOW: KGB Microdot viewer with partial button concealment
BELOW: Microdots found in possession of British KGB spy Helen Kroger with (right) enlargement of one dot.
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