RSA doesn't largely depends on the existence of computer, it could've been used "by hand" using the math behind it. The reason why was not is because, prior to computer, there was not a problem of "sharing" the key (and btw Nazi knew that a single key was weak, that's why they'd change it everyday to encrypt the communication with enigma)
> I would say it's more interesting that one-time pad encryption was not invented and used much earlier than 19th century
That's not true, as I mentioned Cesar's cipher is an example of that, though of course uses a simple key. Radio communications (and of course internet later) is the reason why encryption started to boom on the early 19th century onwards.
RSA is OTP?
In other words, the "inconvenience" of doing a Caesar cipher by hand is nowhere near comparable as doing an RSA cipher by hand.
If people were able to do that in 15th century by hand I don't see how who really needs it couldn't.
Is just the needs were different, but is not complicated
Lol. There is a new dude sitting in a castle one sea over. You want to communicate with them. Let’s say you want to agree to attack a third neighbour at the same time. If your message gets intercepted you will be in trouble.
How do you share your secret keys with them? Mind you, you don’t really trust any of your man, and the sea route is treacherous so you don’t fancy risking going in person.
Sharing keys is a problem old as time.
Why didn't people came up with a manual "RSA" before. Since the math is 400 years old.
We actually did that in university; the public key we used was something like 91 (not hard to factor). Wikipedia has an example with 3233, and that's already very cumbersome: https://en.wikipedia.org/wiki/RSA_(cryptosystem)#Example
It can be done manually easily
I wish there was some way to simplify the math to allow doing it by hand. It would be a nice way to check for correctness while computing it offline, and while ensuring dependencies hadn't been compromised to produce a fake public address.
People can get shockingly good at that kind of thing with enough practice.
I would say it's more interesting that one-time pad encryption was not invented and used much earlier than 19th century. It has obvious military and intelligence uses and is simple enough to be executed by hand.