[Cryptography] Leo Marks' 1998 talk about WW2 SOE code-making and breaking

[Jon Callas]

> On Jan 21, 2026, at 09:58, Kent Borg <kentborg at borg.org> wrote:
> 
> In the talk he made it sound like OTP became a real thing, but he also still seemed exasperated, decades later, at how hard it was to deal with the companies who produced the printed silk the SOE agents needed. (I bet they kept violating the clearly silly one-time aspect.) The WOK was much more frugal with key material, possibly OTP was always more his goal than ever a working reality. After all, the title of the book, Between Silk and Cyanide, is the tension between the value of silk vs the value of the SOE agent's life.

Between Silk and Cyanide is an amazing book, and you really should read it. It's a book that has directly influenced me over and over and keeps coming back to me.

A thing to remember about it, though, is that he never just comes out and says they were doing one-time pads. He says that they developed some unbreakable system, so unbreakable that he really shouldn't talk about it. (By the way, the background banner photo in my LinkedIn profile is an SOE silk pad, and there are lots of images available on the web, including <https://people.duke.edu/~ng46/collections/crypto-silks.htm>. I got it by searching for "SOE one time pad on silk".)

This led to a bunch of "huh?" commentary at the time, because we all knew about the SOE one-time pads. So lots of people wondered if he had some other thing up his sleeve, and what it might be. It turns out that in the book, he was concerned he was still bound by secrecy not to mention details, but by the time he made this audio recording, such things had been sorted out. From my listening, I think he even leans into saying explicitly the things he dances around in the book. Be prepared for that disappointment when you read the book, this is a great recording to listen to because he's all brass tacks in it, unlike how he was in the book.

	Jon