Manual for the Solution of Military Ciphers

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Manual for the Solution of Military Ciphers is a text that was written in 1916 by United States Army Captain Parker Hitt. The book was essentially a manual for the military to improve and refine the security of their communications, specifically in the fields of cipher work. Some parts of the book are now quite outdated, but the main body of the work is still highly valuable as a historic manual on cipher breaking and still of great value for amateur and professional cryptographers due to providing many basic principles of the field that are relevant even now.

Has nothing to do with Louis Cypher.

Tropes used in Manual for the Solution of Military Ciphers include:
  • The Book Cipher: Mentioned in the intro, but noted as being outdated for modern uses for military purposes.
  • Complexity Addiction: Highly discouraged for cipher work. Hitt cites Dutch cryptologist Augustes Kerckhoff's contention ciphers need to be idiot-proof for a single person to operate without overly complicated rules. It is further pointed out making the cipher overly complicated is just as much a headache for the intended users as it is for the enemy, if not more so.
  • Captain Obvious: The miner proverb Hitt cites: Gold is where you find it.
  • Determinator: Noted as a prerequisite for being a successful cipher breaker.
  • Keep It Foreign: An advised technique to make ciphers hard to break was to make sure its conventions would be highly unorthodox to the party who might be expected to try breaking it.
  • Linear Warriors, Quadratic Wizards: A variation of this logic was used in his comparison of transposition and substitution ciphers. The former was the "Linear" because despite it's the ease of use and adaptability, it's long-term security was terrible because transposition follows a route, and once the enemy figures out the path the encipherment follows, the whole message security is compromised. The substitution cipher was deemed the "Quadratic" because while very simple ones were quite weak in terms of security, a cleverly constructed substitution cipher could be absurdly hard to break and even breaking part of a substitution cipher did not necessarily lead to immediate compromise of the entire cipher.
    • Take a Third Option: Combinations of both methods were deemed useful depending on how they were combined, but Hitt noted these could be quite weak if they combined the weaknesses of the separate methods as opposed to their strengths.
  • Older Than They Think: Nigh all substitution ciphers were noted to have origins in principles dating back to the late 15th century, no matter how original their creators assumed them.
  • Reading the Enemy's Mail: A how-to manual for doing this is the rationale of the text. The intro even points out this is how modern military espionage gets most of its information as opposing to stealing intel from the enemy messengers since ciphers are usually sent via wire or radio.
  • Real Life Writes the Plot: Hitt wrote the book around the time it was getting likely the US ability to remain neutral during World War I was rapidly diminishing as a warning that they needed to be prepared for such an eventuality. A year later, and he was sent over to administrate the code and cipher staff detailed to the American Expeditionary Force based on his prescient foresight prior.
  • Spotting the Thread: Hitt noted most ciphers written by different countries had key tells that would identify them, such as frequently used letters endemic to their language structure.
  • Spy Speak: Discussed. Hitt noted codes based on this are not very practical save for specific tactical purposes, and then only for short-term uses.
  • Technology Marches On: At the time of publication, Hitt noted codes were becoming obsolete for military use, save for brief and specific tactical codes.
    • He also noted that most codes and ciphers are not as new as their creators think, then or even now, as most of the basic principles of any modern cipher are based on precedents established centuries and even millennia prior.
  • Vast Bureaucracy: Hitt notes this is the bane of getting anything done efficiently and that cipher bureau stations and offices need to keep themselves coordinated and up to speed on the progress of each other regularly to ensure efficient turn-over time for cipher work.
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