Between Silk and Cyanide

by Leo Marks

  ‘What’s he after?’

  ‘He’ll tell you himself.’ He looked at me critically. ‘The commander has no time to waste, so you’d better be on top form for him. Go home early. That’s an order.’

  He dismissed me before I could question him further.

  I sent a message to the Jedburghs: ‘Message out, rescue op mounted, wish you all merde alors.’

  I had a feeling that at ten o’clock tomorrow I’d be needing it myself.

  Note

  * Photographed on to soluble paper and issued to one of those present as a reserve poem.

  SEVENTY-THREE

  Self-Defence

  We all need a centre

  A core we can rely on

  Our private Mount Zion

  Which all can see

  But none can spy on.

  Written on the eve of Commander Denniston’s visit

  The most unnerving part of Denniston-Day was its tranquil start – only eight indecipherables were waiting to be broken, only three agents had lost their silks and only two lots of codes had been sent to the wrong stations. Better still, there were only three messages from Cairo demanding more WOKs and LOPs, only one request from Melbourne for more briefing officers and only two agents had used the same WOK keys twice.

  By the time I’d persuaded the latter’s country sections to remind them of their instructions it was ten o’clock.

  Commander Denniston had an open manner, though every hair of his head seemed shampooed with secrets, and I was relieved to find that I could look a Bletchley wizard in the eye with some sense of parity, as he was no taller than I was.

  Declining my offer of refreshments – an unpromising start – he said that he’d heard a great deal from Nick and others about the codes we were using and wanted to see them for himself.

  Longing to ask who the ‘others’ were, I pointed to the codes on the wall, which he’d already taken in at a glance. ‘There they all are, sir. Please help yourself.’

  He nodded his acceptance, and I christened his walk ‘the Bletchley two-step’.

  He had a unique way of examining the silks. He seemed to inhale them like Father testing a Havana for counterfeit leaf, asking me pertin-ent questions as he passed from one to the other and nodding at my answers (he turned out to be an expert in nod-language). He seemed particularly interested in the code books (especially the one I’d delivered to the FFI) and asked if much use had been made of them.

  I replied that most agents preferred to encode their messages directly on to one-time pads as it took less time.

  ‘That’s disappointing – especially as the code groups reduce Morse mutilation.’

  I hadn’t pointed this out.

  As he put the code books aside, I was suddenly convinced that I’d done something wrong and that it wasn’t only codes he was here to examine.

  WOKs came next. ‘Isn’t this the system you showed John Tiltman because you needed his blessing before you could use it?’

  ‘Yes, sir. He’s their godfather.’

  ‘You couldn’t have a better.’

  I realised that he knew about Tiltman’s visit and wondered what other homework he’d done.

  I wish to Christ I knew what the little sod’s after.

  He questioned me closely about WOK production and wanted to know why we preferred keys made by hand to the machine-made keys supplied by Bletchley.

  I explained that Bletchley hadn’t produced them in sufficient quantities and that the ones which they’d sent us didn’t seem to me as random as the keys the girls produced by shuffling counters.

  He looked at me doubtfully, so I gave him six sheets of keys produced by the girls and six by Bletchley. He correctly identified Bletchley’s, agreed there was a pattern to them and asked if I’d drawn their attention to it. When I admitted that I hadn’t because we were so grateful to Bletchley he suggested that I did so at once as it might be helpful to them.

  Surely these are minor matters for a man with no time to waste?

  His next comment made me wonder even more what his new job was and where the hell this was leading.

  He said that he’d heard from Nick that I’d devised a deception scheme called Gift-Horse. ‘I’d like you to explain its function, and then show me some examples.’

  I was ready to discuss anything, but Gift-Horse was the one subject I wasn’t prepared for, as Nick rarely enquired about it and I didn’t believe that he’d absorbed its technicalities.

  ‘The function of Gift-Horse is to make WOK messages look as if they’ve been passed in poem-codes to waste the enemy’s time and make our traffic more trouble than it’s worth.’

  ‘Method?’

  ‘Without agents knowing it, we repeat the indicator groups on their WOKs to make it look as if they’ve used the same keys twice, though they’re different every time.’

  ‘Examples?’

  I removed twelve Gift-Horsed WOKs from the safe and spread them in front of him in silence.

  He examined each one carefully, and I could tell from his nodlanguage that he’d spotted the repeated groups at a glance. I then made the mistake of saying that we also Gift-Horsed our dummy traffic.

  ‘What dummy traffic?’

  I explained that we transmitted dummy messages round the clock to hide the volume of our real traffic and without being asked showed him six examples.

  Nod nod frown frown nod nod. ‘I’ve two questions about Gift-Horse.’

  He’s letting me off lightly.

  ‘You display Top Secret material on the walls of your office, so why do you keep Gift-Horsed WOKs in a safe?’

  ‘To stop me from gloating over them.’

  ‘You’ve good reason to.’

  Then why does his voice have an edge to it?

  ‘My second question’s this. Have you discussed Gift-Horse with John Tiltman or anyone else at Bletchley Park?’

  He could tell at a glance that I hadn’t.

  ‘Did you think it wouldn’t interest them – or that it was none of their business?’

  He didn’t wait for an answer, which was just as well, as I’d need a year to find one.

  ‘I’ll come back to that later.’

  If you must.

  ‘I’m going to ask you a question about letter one-time pads, and I want you to consider your answer carefully.’

  Safe ground at last.

  ‘Do you believe they’re breakable on a depth of two?’

  I dropped my unlit cigar. I couldn’t believe that an expert cryptographer was asking me a question which a FANY coder could have answered without the slightest difficulty.

  ‘Take your time.’

  ‘I’m certain they can be. I’ve done it myself with the help of the FANYs.’

  He immediately asked for details, and I became more convinced than ever that I was on some kind of trial.

  Still wondering what the hell I’d done wrong apart from being born, I said that despite our warnings that used code groups must be destroyed at once, agents often used the same ones twice; in order to see how much damage a ‘depth of two’ caused I’d asked a supervisor to encipher two messages on the same code groups without telling anyone the texts (which were scabrous), and after feeling our way for twenty-four hours the girls and I had cracked them.

  ‘How?’

  What’s he expecting – a cryptographic breakthrough?

  ‘Nothing new, sir. I used the system I’d been taught at Bedford but adapted it a bit.’ I showed him the adaptation which I’d passed on to the girls and wondered why he spent so long studying it.

  ‘Has anyone else seen this, apart from you and the coders?’

  ‘No, sir.’

  Good God, he can sigh.

  ‘… Perhaps there’s something else I should mention, sir.’

  ‘I’ve little doubt of it.’

  I added that although one-time pads were simple enough to be agent-proof, they’d found so many ways to send indecipherables in them that I’d given the girls ni
ne guidelines on the quickest way to break them.

  He studied them in silence, then asked if I’d sent a copy to Tiltman.

  He didn’t wait for my answer. ‘Why not?’

  ‘They’re so elementary by Bletchley’s standards.’

  ‘I see. I suggest you send them copies of the guidelines and the “adaptation”, if possible today. I’d also like copies myself.’

  I made a note to despatch them because I knew I’d want to forget it.

  ‘It’s Denniston with two “n”s … Nick will know where to send them.’

  I looked up to find him studying me intently.

  I’ve been sucked into the inner space of an uncluttered mind.

  ‘I doubt if you confine your deception schemes to WOKs and dummy traffic … Do you ever Gift-Horse one-time pads?’

  Is the bastard telepathic?

  ‘I’m working on a way to do it, but it’s still only an itch. I’ll be scratching it tonight.’

  He asked me to tell him the principle (a word seldom used in SOE).

  ‘It’s to make one-time messages look as if they’ve been enciphered on the same code groups … It could waste a lot of the Boche’s time if they fall for it.’

  ‘Keep scratching … Which brings me to my next point. I understand you’ve devised a mental one-time pad.’

  Is there anything Nick hasn’t told him?

  ‘How’s the system work?’

  It usually took me an hour to explain the complexities of a MOP, but he nod-nodded his way through them in under five minutes and had only one question. ‘Have you shown this code to Bletchley?’

  To which I had only one answer – ‘No. I thought it was secure enough not to need vetting.’

  ‘Of course it bloody well is, but that’s not the point …’

  Controlling his anger (but only just) Commander Two Ns abruptly changed the subject. ‘A year or so ago you showed Tiltman some charts you’d devised for breaking indecipherables—’

  Forestalling him, I said that I’d sent the charts to Bletchley.

  ‘But surely you’ve amended them since then?’

  ‘Well … here and there.’

  ‘What’s your current breaking-rate?’

  ‘Ninety per cent in under six hours.’

  ‘Send the amendments to Bletchley.’

  He waited impatiently while I made a note, then jerked his finger at the FFI code book. ‘How long after you’d broken the secret French code in front of them did you deliver that code book to Algiers?’

  I was no longer surprised by anything he knew or asked. ‘Five or six weeks.’

  His next comment was more to himself than to me: ‘That code book’s clearly intended for de Gaulle’s provisional government.’

  Is that why he studied the vocabulary so carefully?

  ‘Do you supply code books to any governments-in-exile?’

  ‘We supply them to their agents, but I doubt if the vocabularies would be much use to their governments …’

  Wondering if this were a clue to his job and wishing he’d go back to it, I suddenly remembered the Bardsea episode. ‘We had to send two hundred one-time pads to the Poles for an unspecified purpose.’

  ‘Ah.’

  It was then that I saw a new Commander Two Ns. Glancing at his watch as if it had been Gift-Horsed, he said with a hint of shyness that he’d be glad of some coffee if the offer were still open.

  ‘Absolutely.’

  I pressed the buzzer twice, and a few moments later the sight of Muriel carrying in her tray had its customary effect, even on him. He accepted the coffee gratefully but declined the sandwiches as he’d arranged to have lunch with Nick. But despite his friendliness, something warned me that he was about to make a meal of me.

  I hadn’t long to wait. ‘It’s time I spoke to you frankly …’

  I noticed how bright his eyes were, though they could no longer conceal how long they’d been open.

  ‘You have great responsibilities, and you don’t need me to tell you that you’ve done a damn good job – you started off with poem-codes and ended with all this …’ He glanced at the silks but seconds later his tone stopped matching them.

  ‘It’s not your ability I’m questioning, it’s your attitude …’ He leaned forward until we were only a few miles apart. ‘Don’t you realise that Bletchley has to deal with all grades of cipher and needs every bit of help it can get? Hasn’t it occurred to you that some of your unorthodoxies would interest them greatly – Gift-Horse and MOPs to name only two? But what chance do you give them to judge for themselves? You wait for people like Dudley-Smith to visit you a couple of times a year and then show them the minimum. Why must you be so damn insular? You don’t strike me as being modest, but surely you’re aware that your approach to codes is, to say the least, uncommon, and could be of the utmost value to Bletchley and others. I urge you from this moment onwards to pass on new ideas like Gift-Horsing onetime pads, because SOE isn’t the only organisation trying to kick the Boche in their cryptographic balls … and now, if I may, I’ll try one of those sandwiches.’

  He tried two but I didn’t join him because I knew that he hadn’t quite finished with me.

  ‘John tells me that you’ve still not visited Bletchley.’

  ‘No, sir.’

  ‘Why not?’

  ‘I might want to stay there.’

  ‘They might even let you’ – his eyes twinkled – ‘if only because you’re the one that got away.’ He looked slowly round the office. ‘Perhaps it’s as well that you did.’

  He stood up and held out his hand, which was a lot drier than mine. ‘You’ve been more help to me than you can possibly know.’ He closed the door quietly.

  I still didn’t know what he did or why he’d come.

  There’s a club among senior signals officers and I’ll never be admitted to it, and aspects of the code war I’ll never understand*

  Ten minutes later I began Gift-Horsing LOPs.

  Note

  * Some fifty years later I met Commander Denniston’s son Robin and learned that Denniston senior left Bletchley in ’42 to take charge of the department which specialised in breaking diplomatic traffic. To this day neither of us knows the purpose of his visit or how I was of help to him (though I do know how much his son has been able to help me throughout the writing of this book).

  SEVENTY-FOUR

  Taken for Granted

  During the past two months, which felt more like centuries, SHAEF had made radical changes to SOE’s structure, many of them long overdue.

  On 1 May they’d ordained that SOE in London should henceforth be known as Special Forces Headquarters and that our OSS counterparts should cease calling themselves O/S and adopt the same cover.

  In mid-June they insisted on amalgamating our rival French sections and gave Buckmaster and Passy an outer limit of 1 July in which to place themselves and their resources under the command of General Koenig, head of the EMFFI (Etat-Major des Forces Françaises de l’Intérieur), which had been created for the sole purpose of controlling all resistance groups which had previously worked for either French section.

  SHAEF then implemented a decision which stood the Signals directorate on what remained of its head. They established an SFHQ in France. It was known as Special Forces Advanced Headquarters, and was adjacent to their own Advanced Headquarters. By mid-June it was already in operation and by July many of SOE’s finest (including Robin Brook) had left Baker Street to advise shaef on what the Resistance could deliver.

  There were no communication problems, as all messages between Brook and Co. and London were exchanged in one-time pads, but at the beginning of July Special Forces Advanced (though in Signals matters retarded) HQ informed Nick that it was essential for them to be able to exchange messages at short notice with circuits of agents anywhere in France. They also informed him that this same facility was required by SOE’s representatives with 21 Army Group and the 1st British and 2nd Canadian armies.

&n
bsp; But even that wasn’t all. Army commanders needed to order agents anywhere in France to sabotage specific targets at short notice. It was taken for granted that SOE’s Signals directorate would provide the solution forthwith.

  It took six of us twelve agonising hours to devise a three-way communication system, though we couldn’t be sure it would work.

  A week later it was fully operational. All messages for agents were relayed to London by SFHQ, and we then re-enciphered them in the agents’ own codes and retransmitted them. Conversely, agents sent their replies to London in WOKs or LOPs and we re-enciphered them in one-time pads, and retransmitted them to SFHQ. With Nick’s backing I’d refused to allow any of the three-way traffic to be retransmitted in the poem-codes which still bedevilled segments of our traffic.

  The urgency of the messages was unlike any we’d known, and the code rooms in London and our three WT stations had to pool their resources to minimise delay.

  But by 1 July the satisfaction of watching the girls achieve impossible targets was put into perspective by one of the most sickening telegrams ever to pass through the code room.

  It was transmitted by Roger (Francis Cammaerts), who’d been appointed head of all Allied missions in south-eastern France and who’d organised Jockey, a railway-demolition network in the Alpes-Maritimes, which was on a par with Pimento. Cammaerts had repeatedly warned London that without the heavy weapons which the Americans had promised to drop, the freedom fighters at Vercors would have no chance of withstanding a major German counter-attack, and he was convinced that they’d be wiped out if they didn’t disperse immediately.

  A week later the Germans landed crack SS troops on the Vercors plateau and overwhelmed the lightly armed Maquis. In the carnage which followed one woman was raped by seventeen men in succession while a German doctor held her pulse, ready to restrain the soldiers if she fainted. Another woman was disembowelled and left to die with her intestines wound round her neck. A third had the fingers of both hands amputated.

  It was no consolation to the girl who decoded the message to learn from subsequent messages that the Americans had broken through in Brittany, that the SAS and the Resistance had secured the Breton countryside and that the Jedburghs had finally (and successfully) gone into action. She asked to be transferred to other duties, and I put her to work Gift-Horsing WOKs.