Between Silk and Cyanide by Leo Marks Read Free Book Online Page A

priority' attack on this kind of traffic would mean that the bulk of Germany's cryptographic manpower would have to be deflected on to SOE—which would in itself be a major contribution to the war effort.
    Indecipherables would be reduced to a minimum because we would no longer have to play the guessing-game, 'Which word has he misspelt?' The worked-out keys would also be proof against Morse mutilation, which frequently rendered perfectly encoded messages indecipherable because the indicator-groups (telling us which words the agent had chosen) were so badly garbled.
    Silk itself was easy to cut, easy to burn and easy to camouflage. If the Gestapo or Vichy police ran their hands over an agent's clothing during a random street search, silk sewn into the lining could not be detected.
    All the resources of the Gestapo would not force an agent to reveal a code he could not possibly remember. Destroying his worked-out keys as soon as he had used them must become as reflex to an agent as pulling the ripcord of his parachute.
    But there was one thing for which he could still be tortured. His security check. And this to me was the most haunting and daunting issue of all. If we couldn't solve this problem, we had solved nothing. For the first time I found myself wondering how best to put something to that silent, motionless figure with his unlit cigar. 'I need two minutes, Tommy.'
    I grabbed a sheet of paper and started scribbling. Tommy would know if what followed was right, and I would be bound by his judgement.
    When I'd finished, I wrote something on the blotter in front of me and covered it with an ashtray. I then showed him my scribbling. It was intended to be an artist's impression of how a silk code would look. All it lacked was the artist:
OUTSTATION TO HOME
14. 2.13. 4. 6.13. 1. 5. 7.15. 3. 9.11.16.10. 8.
 6.10.13. 2. 4.11. 7. 9.12. 3. 5. 8. 1.
CEDQT
 9.10. 1. 7.11. 4.12. 8. 5. 2. 6.13. 3.
11. 5. 7.12. 2. 6. 3. 8. 9. 1.10. 4
PKBDO
 2. 9. 5.10.14. 1. 6.11. 4.15. 8. 3.12.12. 7.
 4. 6. 1. 5. 7. 9. 2. 1.13. 8.12.10.
RYTGE
 6. 3. 7. 4. 8. 9. 2.10. 5.11.13. 1.14.12.
 3. 1.10. 4. 6. 2. 7. 8. 5. 9.11.
UVHJG
 4. 7. 8. 1. 9. 2.10.11. 3. 5. 6.12.13.14.
 4. 6. 7. 8. 5. 1. 9.10. 2.11.12. 3.
ZAUBA
    The explanation came out in a rush and a jumble:
    'I'm an agent. Tommy, and I've been caught with my silk code on me. I've destroyed all the previous keys I've used but the Gestapo know bloody well that if they can torture my security check out of me they can use the rest of these keys to transmit messages to London and pretend they're from me.
    'You'll see that opposite each pair of keys there are five letters printed. These are indicator-groups to tell London which pair of keys I've used to encode my message. The next pair I'm due to use are the ones at the top—starting 14.2.13.4. The indicator group is CEDQT. After this I'm due to use the next pair of keys—starting 9.10.1.7. The indicator-group is PKQDO. But I never use these indicator-groups exactly as they are printed. I have prearranged with London always to add 3 to the first letter and 2 to the fourth. Take the indicator CEDQT. C plus 3 is F, and Q plus 2 is S. So, instead of sending CEDQT I send FEDST. Instead of sending PKBDO I send SKBFO.
    At least, that's what I'm telling you because you're the Gestapo. All my previous indicator-groups have been destroyed; how can you know if I'm telling you the truth? Rough me up and I'll change it once again. When do you stop? Now I've written on this blotter what my real secret numbers are. If you can guess 'em, these Havanas are yours—and you'll be the only cigar-smoking Kraut in Baker Street.'
    Herr Forest Frederick von Yeo-Thomas sat in silence for a very long time. I didn't interrupt him—except to say, somewhat nervously, that this was only one of the codes I hoped to introduce.
    By the time the security-vetted cleaning women arrived to claim the