Spycraft - Melton [252]
Only imagination limited the variety of plastic that could be used. MLI chemistry could be applied to eyeglass frames, caps on ballpoint pens, plastic key fobs, credit cards, and even the plastic toothpick on commercial models of the Swiss Army knife. Case officers using an MLI device to “write” invisibly on a piece of paper could carry those safely until returning to the station where a tech developed the notes.
TSD answered a request from the Directorate of Operations in the early 1970s to provide a secure system that would allow a case officer or tech to record and store operational notes on a tape recorder. OTS modified small commercial Sony stereo tape recorders by adding an additional, or “third track” recording head. In use, the tape recorder would function normally to play tapes filled with local music in two channels of stereo. When an officer wanted to record operational notes, he activated a switch OTS had built into the recorder and turned on the secret recording head for the third track. The audio would be recorded on the tape, but on a track that was unreadable on any nonmodified tape recorder, and only an operational listener would know how to activate the switch to listen to the third track.
In a variation on the concept, the clandestine communication branch of MI6 created a similar covert system. Former MI6 officer Richard Tomlinson described it:
The essential feature of these gadgets is that they are noncompromising, i.e., they are identical or virtually indistinguishable from commercially available equipment. Pettle recorders were particularly ingenious. Any normal audiocassette has two tracks running parallel to each other, one for each side of the cassette. Pettle recorders exploit the unused part of the magnetic tape, which lies between the two strips. [We observed] an ordinary personal stereo, which played and recorded on both sides of the tape like an ordinary machine. But turning it upside down tripped a microswitch so that pressing the STOP and RECORD buttons together made the machine record over the central track, while pressing STOP and PLAY together made it play back the recording.41
Codes and ciphers play essential roles in successful covert communications systems. A code obscures the meaning of a message of any kind by substituting words, numbers, or symbols for plaintext (the unencrypted text of the message). A single symbol could represent an idea or an entire message. The signals made with chalk, lipstick, or a thumbtack to initiate a dead drop sequence were examples of codes while the message concealed inside the dead drop had the added protection of a cipher. A cipher represented a particular type of code in which numbers and letters were systematically substituted according to a prearranged plan. Ciphers used a key to convert the plaintext message.
Probably no piece of spy gear was more often issued or more reliable than the one-time pad. OTPs, the only cipher system that was known to be theoretically unbreakable, were composed of one or more pages filled with random numbers arranged in groups of five.42 Only two copies of an OTP were produced—one copy for the agent and one for the handler. To maintain the security of communications, the OTP page and all notes from using it were to be destroyed by the agent as soon as the working session was completed.
OTPs had great advantages and were praised by both agents and handlers. One OTS tech who ran operations in Moscow for two decades stated, “OTPs didn’t let us down. They didn’t leave you or the agent wondering if the communication