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What are the major code breaks in the history of cryptography? Which code breaks changed the face of a battle or another major event? Which one had nationwide consequences?

Maarten Bodewes
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crypt
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  • Purple first comes to mind. See also this on the Hagelin C(X)-52, which can be regarded as a break from an operational standpoint. – fgrieu Feb 20 '17 at 07:49
  • The Zimmermann Telegram – r3mainer Feb 20 '17 at 10:54
  • @ Raza: Such broad and list-alike questions aren't very welcome at our site. What research have you done? See, sharing research efforts helps everyone! Tell us what research you did, what you found, and why it didn’t meet your needs. That shows users you took time trying to help yourself, it saves us from reiterating obvious answers, and (most important) it helps you to get more relevant on-point answers. At worst it will help you frame “a better question”; at best it might even answer it. – e-sushi Feb 20 '17 at 16:55
  • @ everyone: As our help center as well as the comment-edit-field placeholder text both explain, comments are not meant to be used to post potential answers, to chat (we've got chatrooms for that), or to discuss things endlessly. Comments are only meant to be used for clarification and/or to suggest enhancements to the related question or answer. To keep the noise down, things have been moved to chat. – e-sushi Feb 20 '17 at 17:04
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    Right now, I have to agree with @e-sushi that this question is likely too broad or at least unclear what you're asking. Please specify exactly what you want to know, how much you want to know about it and about which time-frames we are talking about (pre-industrialization? Pre-Computer? Modern-Age?). – SEJPM Feb 20 '17 at 19:55
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    There is a similar Q – *Examples of modern, widely used ciphers that suddenly fell?* – on the site already, but seems less focused on history-changing results. – Ella Rose Feb 20 '17 at 20:20
  • @TMM Let’s simply continue talking about your meta question et all in the already existing chatroom. – e-sushi Feb 20 '17 at 21:42
  • @Raza You should edit the community answer rather than your question. :) – Biv Feb 22 '17 at 09:53
  • @Biv editing question mean i am expecting others to come up with breaks other than mentioned in the question to qualify as answer – crypt Feb 22 '17 at 09:56
  • This is an ultra broad question. Why is isn't it put on hold? –  Mar 16 '17 at 07:54
  • It's a duplicate of https://crypto.stackexchange.com/questions/34999/examples-of-modern-widely-used-ciphers-that-suddenly-fell –  Mar 16 '17 at 07:55
  • @Raza You wrote "The few examples/programs i found are:" - From what I read here, most were mentioned by others and not you. The early versions of the question have nothing listed at all. – tylo Mar 16 '17 at 11:15
  • @tylo once i posted question, i knew about enigma, venona and purple, but i didnt mention it in the question, later on i added the list in question so that people can answer other than the list, i came to know about others and i kept on adding these in the list. The breaks mentioned in answers of others, i have not added in the question like Crypto AG, Queen Mary of Scots. Zimmerman is the only entry which i came to know while searching and it was also mentioned in an answer :) – crypt Mar 16 '17 at 11:25
  • @Raza Even if this is just a minor detail, give credit where credit is due. If someone else mentions it first, it's entirely irrelevant to the question if you knew it previously or not. You did not mention it yourself. Claiming "I found this on my own" can't be verified - and in other contexts this would qualify as plagiarism. Anyway, you should only list things which you had researched previously to asking - not try to give part of an answer in the question. And finally: I think this question is too open, opinionated (what is "major"?) and not a good fit for the site at all. – tylo Mar 16 '17 at 14:24

2 Answers2

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Besides the ones mentioned in the already existing Q&A "Examples of modern, widely used ciphers that suddenly fell?", the following major code breaks have been notable in history:

Maarten Bodewes
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The case of the Queen Mary of Scots is interesting. She paid with her head the cost of using a weak cipher (breakable with frequency analysis). But that happened many centuries ago so ciphers using complicated substitution were the best option at the time.

For more details:

BBC - History - Elizabeth's Spy Network

Mathieu Dostie
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