In Ken Follett's WW2 spy novel Jackdaws, there's a point where a British agent para-drops into France. He has with him a codebook for a one-time pad to communicate back with HQ. However, he is captured by a German counter-intelligence officer who then uses his codebook to send fake messages instead.
Back in England, the protagonist becomes suspicious that this has happened and comes up with a clever way of checking his suspicion. He has the telegraph operator intentionally make mistakes (typos) in a response to the agent. Supposedly if it were a real agent, he would react with an angry message, abusing the operator for making mistakes. Since the German responds normally, he is revealed.
So, my questions:
Would telegraph operators actually have been held to such a high standard for this kind of ruse to work? Would a spy really get angry at the operator over a few typos? Would this have been any different for German telegraph operators?
Was this kind of cryptography commonly used by British agents?
Didn't the British have any actual method for authenticating messages encrypted in this manner? It seems like just having a challenge/response system with different codes for "safe" vs "under duress" would work. A one-time pad is unbreakable, but not having any way to authenticate messages seems like a huge oversight, given the high risk of an agent being captured along with his codebook.
"Between Silk and Cyanide, A Codemakers War, 1941-1945". Was written by Leo Marks, who left his father's famous bookshop at 84 Charing Cross Road at the age of 22 to fight WWII. He was quickly recognized as a genius cryptographer, and became Head of Communications for the Special Operations Executive (SOE) which sent operatives into occupied Europe.
Marks constructed all the codes which the SOE used in WWII, and he was well aware of the strengths and weaknesses of them. His book goes into all of this and is an incredibly good read.
After the war, Marks became a well known writer of screenplays. His vivid and polished authorial style makes this a standout war autobiography, and his career as an incredibly young top cryptographer, training some of the most famous agents dropped into occupied Europe makes this one of the best books written about the espionage war.
If you read this book you will get an insight into all your questions, from the man responsible for thinking about them. He was well aware (and frustrated) by some of the weaknesses in the encryption systems given to agents, and had suspicions early on that some of the agent networks had been broken and taken over by the Germans. He goes into some of the politics which either led to solutions being found, or not.
Anyway, one of the very best books about the secret wars of WWII and the codes and encryptions associated. Recommend it highly.