Between Silk and Cyanide (5 page)

Looking at me intently, Hambro asked how long I had been with SOE. When I told him two months, he instructed me to continue asking questions until I found the right answers, his tone suggesting that he knew this would not be easy. He then said that it was time I went home, and strode down the corridor like an elephant in slippers. An hour later he was running his bath.

SOE regarded the Signals directorate as a benign post office which delivered the mail more or less on time, could be given a kick in the transmitters if it didn't, but never caused anyone the slightest bother. The last thing the country sections expected was that a junior member of that inoffensive directorate would call on them—on the absurd pretext that the new codes he was devising must be shaped to meet their long-term requirements. Many times during that fact-finding tour I felt as if I were travelling across Europe in a carry-cot with a suspect visa.

No matter which country section I visited, everything was in short supply except confusion, and it was easy to mis-assess country section officers because the constant need for improvisation made it difficult to distinguish the few who understood their jobs from the majority who didn't.

That was the marvellous and the terrifying part of SOE in its adolescence: it was pitted and pockmarked with improbable people doing implausible things for imponderable purposes and succeeding by coincidence. One thing alone made it worth the price of the ticket. It was at the low levels at which I mixed—amongst the people SOE hadn't really know it had—that the excitement of discovery really lay. It peaked and stayed there whenever I met the proud holder of the title 'Chairman of the Awkward Squad'—Flight Lieutenant Yeo-Thomas, who was one day to change his name by Resistance Movement deed poll to 'the White Rabbit'.

'Our Tommy' certainly wasn't everyone's Tommy. Many people in SOE disliked him intensely but that wasn't his only recommendation. He spoke bilingual French and had spent most of his life in France amongst Frenchmen. In 1939 he was general manager of one if the world's most famous fashion houses—Molyneux of Paris, then t the
haute
of its
couture.
He 'persuaded' the RAF to let him enlist as a ranker at the age of thirty-eight. Three years later it was SOE's turn and he joined RF section as pilot-officer.

Not even SOE could miss his immediate impact on the Duke Street intransigents. To his superior's astonishment he was able to criticize the Free French to their faces without causing a national temper tantrum and was the only Englishman actually welcomed into Duke Street by de Gaulle's fearsome right fist, young Colonel Passy. After Churchill, the man Tommy most admired was de Gaulle, and the Free French respected him for it even if Baker Street didn't. But there was one aspect of Tommy's conduct which worried SOE's hierarchy even more than his loyalty to Duke Street. He had earned his coveted tie because he refused to obey SOE's house rule forbidding officers in different country sections from exchanging information. Tommy was always prepared to compare notes on the Gestapo, and similar obscenities, with anyone in SOE of whatever nationality; in the insularity which passed for security, few responded.

He hadn't waited till the Christmas after next to see for himself how indecipherables were broken. He'd looked in a few nights after tor first meeting and ever since then we'd indulged in a series of late-night chat-shows during which we exchanged grievances, and shared the Havana cigars which I'd stolen from my father.

There were only two subjects which we never referred to. I didn't tell him that I was keeping a 'watching brief' on de Gaulle's secret code, and Tommy for his part never tried to involve me in a discussion about the rival French section run by Buckmaster, which recruited from those who owed no allegiance to de Gaulle. He disapproved of the principle of there being two French sections to win one war and left it at that.

One smoky midnight, when I hadn't seen him for about a week and was almost missing him, I was struggling with an indecipherable from a Norwegian wireless operator named Gunwald Tomstad, Wilson had told me that the Admiralty was anxiously waiting to read Tomstad's message, and wanted to pass its contents to 'a former naval person'. And then, as if reference to Churchill was not sufficient incentive, Wilson proceeded to warn me that if we hadn't broken the message before Tomstad's next schedule—which was only a few hours away—he would order him to re-encode and repeat it no matter what the consequences.

I thought of all the things Tomstad had done right as I tried to rectify what he hadn't.

He was a farmer who lived near a sea-port and regularly reported the movements of U-boats. He seemed to regard submarines as an extension of his livestock and his reports had already dispatched six to market, with two 'possibles'. But U-boat spotting was only the fringe of farmer Tomstad's war effort.

In 1941 he had been wireless operator for Odd Starheim (code-name Cheese) and had sent a message from Starheim reporting that four German warships were hiding in a fjord. The Admiralty immediately despatched the Prince of Wales and the Hood, and the subsequent sinking of the Bismarck and the crippling of the Prinz Eugen were directly attributable to Starheim's messages and Tomstad's operating.

Starheim was now back in London giving Wilson no peace until he was allowed to join Tomstad, and demanding to know the content of his latest message. I tried my thousandth key without success. There was little time left. I didn't hear the door open but knew who was standing there. Tommy recognized the symptoms of 'indecipherabilititis' and asked if he could help. I told him the bastard indecipherable wasn't from France. He shot me a tommy-gun look of utter contempt, then took off his tunic and sat down at the desk.

He spent the next two hours doing the dull, routine job of checking my work-sheets without really understanding them, but it was help beyond price to Tomstad and me. We pierced the indecipherable's hull at three in the morning ('cruiser in harbour disguised as island with tree in the middle'). Tommy didn't even glance at the clear-text. I'd have liked to tell him that it might soon be on its way to the man he most admired, a 'former naval person'—but I couldn't. I went into Dansey's office, closed the door and read the clear-text on the 'scrambler' to the Norwegian duty officer.

I returned to my office to finish the job.

The coders of Grendon had done all they could to break that message, and they deserved the satisfaction of succeeding. I telephoned the night supervisor and told her that I hadn't broken the message and was on my way home. I suggested twenty or so keys, including the correct one, and asked her to pass them to the night squad. I reminded her that if they did have any success, the message must be teleprinted to London marked 'Absolute Priority'. I wished them better luck than I'd had.

Tommy studied me thoughtfully as I gave him his cigar. 'How old are you?' he asked.

'Twenty-three.' I was tempted to be more specific and add 'next month'. I enjoyed presents.

He gave me one: 'Would you like', he asked, 'to tell me what's worrying you?'

I memorized the way he said it so that I could try it on the coders.

'Thanks, Tommy. But it would take all night.'

'I've got all night.'

'It's the poem-code! It has to go.'

'Tell me why. And then tell me what you think should replace it'

'I spared him nothing. My worry had a technical name: transposition-keys. They were the code equivalent of an anxiety neurosis.

Every agent had to work out his transposition-keys before he could either send a message or decode one from us. I wanted Tommy to see for himself the kind of effort this involved in the soothing atmosphere of occupied Europe.

I asked him if there were any particular poem or phrase he would like to use; he left it to me. I wrote one out and told him it was based on an SOE opinion poll:

Y E O T H O M A S I S A P A I N I N T H E A R S E

The lowest letter in that phrase is A. I asked him to put the figure 1 beneath it.

Y E O T H O M A S I S A P A I N I N T H E A R S E
1.

Then the figure 2 beneath the second A, a 3 beneath the third, a 4 beneath the fourth:

Y E O T H O M A S I S A P A I N I N T H E A R S E
1. 2. 3. 4.

The next letter is E. I asked him to put a 5 beneath it. Then 6 and 7 beneath the remaining E's.

Y E O T H O M A S I S A P A I N I N T H E A R S E
5. 1. 2. 3. 6. 4. 7.

Without waiting to be asked, Tommy continued numbering the rest of the letters in alphabetical order until we were looking at:

Y E O T H O M A S I S A P A I N I N T H E A R S E
25.5. 16. 23.8. 17.13.1. 20. 10.21. 2. 18.3. 11.14. 12.15. 24.9. 6. 4. 19.22.7.

That numbered phrase was called a transposition-key. I broke the good news that all messages were encoded on a pair of transposition-keys—so the agent now had to start numbering another one using, for security reasons, a different five words of his poem. An interesting repeat performance with an uninvited audience on the prowl outside.

The slightest mistake in the numbering would render the entire message indecipherable. The smallest error in the spelling would also produce gibberish. The permutations of mistakes an agent could make ran into hundreds of millions—and he still hadn't started to encode his message.

To do so, the agent used his transposition-keys to put his clear text through a series of complex convolutions not unlike Ozanne's mind, so that the message arrived in London in jumbled form where we (hopefully) could unscramble it because we (hopefully) were the only ones who knew what his poem was.

Unless the Germans had tortured it out of him.

Or unless their cryptographers had broken one of his messages and mathematically reconstructed the words of his poem.

I told Tommy that the poem-code must go and be replaced by one which the agents could not possibly remember. Their transposition-keys must never again be based on words, poetic or otherwise. They must be mass-produced by hand by specially trained groups of coders shuffling numbered counters at random.

We would give each agent a series of transposition keys already worked out for him—and printed on silk. To encode a message, he would simply have to copy out the keys we had prepared for him and immediately cut them away from the silk and burn them. There should be no way that he could possibly remember the figures he had used. They would all have been selected at random—and would be different for every single agent in the field.

Each silk would contain sufficient keys for 200 messages—100 from the agent to us, 100 from us to him. The greatly increased security of these 'worked-out' keys would allow the messages to be shorter. One hundred letters could be sent instead of the existing minimum of 200.

The cryptographic parlour-game would be closed for the season.

Enemy cryptographers would no longer have poems to reconstruct and would have to tackle every single message individually—an undertaking which was anathema to all cryptographers. Every message to and from the field would confront them with a new code, and to sustain an 'absolute 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:

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.