# Anyone here know anything about 19th century commercial ciphers for telegrams? **URL:** \ **Category:** Factual Questions\ **Created:** [December 12, 2019, 10:18pm UTC](https://boards.straightdope.com/t/anyone-here-know-anything-about-19th-century-commercial-ciphers-for-telegrams/844784 "2019-12-12T22:18:12Z")\ **Posts on this page:** 6\ **Page:** 3
**Author:** ![Rocketeer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rocketeer/32/4437_2.png) [@Rocketeer](https://boards.straightdope.com/u/Rocketeer)\ **Post date:** [December 18, 2019, 4:12am UTC](https://boards.straightdope.com/t/anyone-here-know-anything-about-19th-century-commercial-ciphers-for-telegrams/844784/41 "2019-12-18T04:12:08Z")
> [@Northern\_Piper](#): > > I always thought that one was the worst of the four novels. Ditto here. I’ve read all of Holmes several times, except for **VoF** , which I started once and never finished, and have never looked at since. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [December 18, 2019, 6:11am UTC](https://boards.straightdope.com/t/anyone-here-know-anything-about-19th-century-commercial-ciphers-for-telegrams/844784/42 "2019-12-18T06:11:05Z")
> [@markn\_1](#): > > I guess this technique wouldn’t have been used to encrypt anything terribly important then. I suppose it wouldn’t take more than a couple of minutes to check one key against a message to see if the decryption makes sense. If it were worth it to someone to hire 100 people to work on it, they could decrypt a message in a day or two. That assumes one key per message. What if they’ve agreed that the key will initially be 100, but after ever fifth word, they add five to the key? ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [December 18, 2019, 12:05pm UTC](https://boards.straightdope.com/t/anyone-here-know-anything-about-19th-century-commercial-ciphers-for-telegrams/844784/43 "2019-12-18T12:05:30Z")
> [@Northern\_Piper](#): > > That assumes one key per message. What if they’ve agreed that the key will initially be 100, but after ever fifth word, they add five to the key? Yes. Or they could have a page of numbers and add a new number to each 5 digit group. And pages of numbers were available. But remember: they are doing this by hand, and it’s being done by office workers, not specialists whose friends may be killed if they get it wrong. Even now, most office workers have trouble doing accurate addition without a calculator. ---
**Author:** ![GreenWyvern](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/greenwyvern/32/2834_2.png) [@GreenWyvern](https://boards.straightdope.com/u/GreenWyvern)\ **Post date:** [December 18, 2019, 12:48pm UTC](https://boards.straightdope.com/t/anyone-here-know-anything-about-19th-century-commercial-ciphers-for-telegrams/844784/44 "2019-12-18T12:48:09Z")
> [@Melbourne](#): > > Even now, most office workers have trouble doing accurate addition without a calculator. Before the invention of calculators, most people were a LOT better at mental arithmetic, and arithmetic with a pencil and paper. ---
**Author:** ![whitetho](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whitetho/32/1059_2.png) [@whitetho](https://boards.straightdope.com/u/whitetho)\ **Post date:** [December 18, 2019, 2:01pm UTC](https://boards.straightdope.com/t/anyone-here-know-anything-about-19th-century-commercial-ciphers-for-telegrams/844784/45 "2019-12-18T14:01:02Z")
> [@Kevbo](#): > > Numerals all encode as 5 symbols, and punctuation marks as 6 symbols. I’m going to have to be nitpicky here and note that while this is true for modern-day “International Morse”, a 19[sup]th[/sup]-century U.S. telegram would have been sent using the much different [American Morse](https://en.wikipedia.org/wiki/American_Morse_code), which used significantly different dot-and-dash sequences for the numerals than that used by International Morse. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [December 18, 2019, 3:34pm UTC](https://boards.straightdope.com/t/anyone-here-know-anything-about-19th-century-commercial-ciphers-for-telegrams/844784/46 "2019-12-18T15:34:10Z")
> [@Northern\_Piper](#): > > That assumes one key per message. What if they’ve agreed that the key will initially be 100, but after ever fifth word, they add five to the key? That’s just a crude way of making the key longer. Cryptanalysis usually assumes Kerckhoff’s Principle – the enemy knows your algorithm but doesn’t know your key. So whether he has to guess one long number or two short ones is irrelevant. I estimated 1-2 days to exhaustively search for a 5 digit key. The numbers you’re currently using are shorter than the 5-digit key you mentioned earlier. A 3 digit primary key and one digit secondary key is actually 10 times easier to crack than a single 5 digit key, and could be done in a couple of hours with a team of 100. You’d really want to use a 5 digit primary key and a long, maybe 5 digit, secondary key, adding them mod 100,000. But of course, this is all based on modern understanding of ciphers, which didn’t exist in the 19th century. [Previous page](https://boards.straightdope.com/t/anyone-here-know-anything-about-19th-century-commercial-ciphers-for-telegrams/844784.md?page=2)