For example if Tom wanted to send a secure message to Suzi he would encode his message with Suzi’s public key and send it to her. The message can only be decoded using Suzi’s secret private key that only she knows.

Interesting thing is that a private key is made of two large distinct random prime numbers. And a public key is the product of those two numbers. So RSA is only as safe as it’s hard to find those two prime numbers using the public key to get the private key. But more interestingly it turns out to be almost impossible. There is no such efficient algorithm on earth to find those two prime numbers using a public key. It would take years to decrypt a single number. You can actually earn some money trying to decrypt RSA messages.

RSA key’s are typically 1024, 2048 bits long. A shorter 256 bit key can easily be decrypted using a home computer. A 512 key can be decrypted with a Computer Cluster. Even 1024 is not considered really safe anymore. Even more Shor’s algorithm proves that a RSA key could be decrypted as fast as a computer can do a quick sort. Though that would require us to have a quantum computer. It’s a theoretical device by now but who knows what the future holds?

There are other security attacks known, but they are way too much complex for a simple presentation like this. So..

Shop safely!