This comment from Reddit math, in response to a statement about how people can communicate secrets to each other with a third party listening, has a very small, simple example of public key cryptography:
Take your message, treat it as a number and multiply it by a bunch of primes.
Send it to me. I will then multiply by a bunch of primes too.
I send it back to you. You then divide by all of your primes.
Send it back to me. I divide by all of my primes and get the original message.
This comment has 5700+ upvotes by Reddit math, but it strikes me as unusual because there's no modular arithmetic used, only primes.
Does this example actually work, if sufficiently large primes are used?