Between Silk and Cyanide (35 page)
Read Between Silk and Cyanide Online
Authors: Leo Marks
Tags: #Biography & Autobiography, #Historical, #Modern, #20th Century, #Military, #World War II, #History
| Q r | Q p | Q o | Q a | Q d | Q v | Q x | Q z | Q u | Q b | Q c | Q j | Q k | Q m | Q c | Q s | Q n | Q q | Q h | Q w | Q r | Q l | Q y | Q i | Q f | Q v |
| R r | R p | R o | R a | R d | R v | R x | R z | R u | R b | R c | R j | R k | R m | R c | R s | R n | R q | R h | R w | R r | R l | R y | R i | R f | R v |
| S r | S p | S o | S a | S d | S v | S x | S z | S u | S b | S c | S j | S k | S m | S c | S s | S n | S q | S h | S w | S r | S l | S y | S i | S f | S v |
| T r | T p | T o | T a | T d | T v | T x | T z | T u | T b | T c | T j | T k | T m | T c | T s | T n | T q | T h | T w | T r | T l | T y | T i | T f | T v |
| U r | U p | U o | U a | U d | U v | U x | U z | U u | U b | U c | U j | U k | U m | U c | U s | U n | U q | U h | U w | U r | U l | U y | U i | U f | U v |
| V r | V p | V o | V a | V d | V v | V x | V z | V u | V b | V c | V j | V k | V m | V c | V s | V n | V q | V h | V w | V r | V l | V y | V i | V f | V v |
| W r | W p | W o | W a | W d | W v | W x | W z | W u | W b | W c | W j | W k | W m | W c | W s | W n | W q | W h | W w | W r | W l | W y | W i | W f | W v |
| X r | X p | X o | X a | X d | X v | X x | X z | X u | X b | X c | X j | X k | X m | X c | X s | X n | X q | X h | X w | X r | X l | X y | X i | X f | X v |
| Y r | Y p | Y o | Y a | Y d | Y v | Y x | Y z | Y u | Y b | Y c | Y j | Y k | Y m | Y c | Y s | Y n | Y q | Y h | Y w | Y r | Y l | Y y | Y i | Y f | Y v |
| Z r | Z p | Z o | Z a | Z d | Z v | Z x | Z z | Z u | Z b | Z c | Z j | Z k | Z m | Z c | Z s | Z n | Z q | Z h | Z w | Z r | Z l | Z y | Z i | Z f | Z v |
You see the alphabet which runs along the top? Glance down the O column until you come to the L. What does O over L give you?'
'Q.'
'Then that's your first pair of letters encoded. Your next pair is P over O. What does P over O give you?'
'E,' he replied.
'Then that's your next code-group. No great hardship, is it? The third pair is X over N… what does X over N give you?'
'M.'
Eighteen seconds later his task was complete.
One-time pad: OPXCA PLZOR BHTEJ Message: LONGL IVETI LTMAN Code-groups: QEMXK XOTKR JVYFG
In the absence of any comment, such as 'Rise, Sir Leo', I explained the decoding process was just as simple. All he had to do was write the code-groups under the one-time pad groups and the substition square would decode each pair in turn.
Pretending that he really was an agent, I pointed out that O over L had produced Q, and that in the decoding process Q over Q would produce L, and the same principle applied to all the other pairs of letters.
He accepted my word for it without bothering to check, which made me uneasy.
But his frown worried me even more. It was clear that something was puzzling him.
Wondering what I'd overlooked, I explained that agents would use LOPs as their main code, have WOKs in reserve, and fall back on poems if they lost both. I then pointed out that the pads and substitution squares would be different for each agent, and that they'd be given high-grade security checks. I started to describe them.
'Hold on a minute.'
I did—to the desk.
I agree that the pads must be different, but why the substitution squares? Surely it wouldn't matter a damn how many of them were captured? 'What use would they be without the pads? Or have I missed something?'
'No, Commander—I have. Of course they can be the same—you've saved us an enormous amount of work.'
But he was still frowning.
What other idiocy had he spotted?
'Look here. Marks…'
I prepared for the worst.
'… did I understand you to say that you didn't think of this code until after Tiltman had left?'
'Yes! What's wrong with it?'
'Nothing at all… As a matter of fact letter one-time pads have been working very successfully for quite a long time.'
I'd forgotten how to handle relief, and he was closer to being hugged than he'd ever know. It was the equivalent to hearing that Hitler had choked to death on a piece of gefilte fish.
'My God, sir [I'd decided to promote him], that's the best news you could possibly have given me.'
And so it was—but why was he looking at me in such an extraordinary way? Surely he didn't think I was disappointed because I couldn't take the credit for LOPs? Surely to God it couldn't be that?
[18]
'What's the problem. Commander?'
He hesitated for fully ten seconds.
I prepared for the worst.
'The problem is knowing the best way to put this to you…'
Put what, for Christ's sake?
His smile was as unexpected as a self-peeling banana. 'It's quite an achievement thinking up LOPs without any help.'
I was as embarrassed as he was but returned to full alert when his expression hardened.
'I must also say this—and let me emphasize it's just my personal opinion because you've rather sprung this on me… I don't believe SOE needs letter one-time pads—WOKs are far better suited for agents' traffic.'
I asked him to explain why.
His assessment of the codes' relative merits was brusque, informative and apparently impartial. In his view, WOKs had one great advatage: They allowed 200 messages to be passed on only two sheets of silk, whereas for 200 to be passed in LOPs would require a least a dozen sheets of one-time pad.
As for WOKs' security, provided that they were used once only every message would have to be attacked separately, which would place as great a strain on the enemy's resources as it would on Bletchley's. For all practical purposes, we need look no further than WOKs.
He paused for breath but I had none to offer him.
It was true (he continued) that LOP-users could send as few as ten letters but how many agents could take advantage of this? Surely many of them had to transmit lengthy reports? In which case, would't their dozen sheets of pad be harder to camouflage and more dangerous to carry than two sheets of silk? Warning me by eye-glint not to interrupt, he compared the coding demands which each system each system made.
WOK-users had only to copy out one line of figures before starting the process of double-transposition. But LOP-users had to copy out fifty letters of their one-time pads, then write their messages beneath them, and start using their substitution square. Although the system was simpler than double-transposition, the effort involved was just as great, and was likely to take longer.
I pointed out that it had taken him eighteen seconds to copy out his one-time pad groups and write his message beneath them, and another fifty seconds to encipher LONG LIVE TILTMAN. Assuming that agents were twice as slow, they could still encode or decode the average message in under twenty minutes.
Straightening his cuffs, Dudley-Smith said he didn't realize that I'd been testing him for a job in SOE or he'd have put up a better performance. He then made what was clearly his closing statement.
He appreciated that agents had to keep the messages as short as as possible because of the efficiency of the Funk-Horchdienst (the German interception service). But it was equally important that they destroyed the used portions of their codes, and surely it would be easier for them to cut away one line of a WOK than a dozen lines of a one-time pad? Given the choice between WOKs and LOPs he felt that most agents would opt for WOKs.
'Which system would Bletchley opt for if it were faced with breaking it?'
'You know damn well that letter-pads are unbreakable on a depth of one.' (Used once only.)
'Are they produced at Bletchley, Commander? And could you help us to get some?'
In the silence that followed I knew that I must leave nothing unsaid. I told him that I agreed with most of his reservations but the fact remained that 90 per cent of SOE's messages could be far shorter than the minimum of 100 letters required by WOKs, and that if Bletchley couldn't help us we'd recruit a special team of girls and produce the pads by hand.