So, you want to send something via email that's confidential?
The best method of doing this is to encrypt your message. In ancient pre-computing days this was called encoding.
There are many different methods of encryption. The most popular is called public key encryption, often referred to as RSA, an acronym based on the initials of the three people who invented it. It's common on the Internet, especially through Phil Zimmermann's Pretty Good Privacy (PGP).
It's based on the difficulty of factoring large prime numbers. Whether they're all that difficult to factor these days on a supercomputer is an open question. But many people still have faith. And the bottom line is that high-level RSA ecryption (invented in er, 1977) is still good for keeping out casual snoopers. But maybe not so brilliant for keeping out anybody with access to decent supercomputers, such as the intelligence services.
And indeed, why should it be? But lets assume you're more interested in keeping out the average teenage hacker rather than national protection agencies. What level do you need?
Levels of encryption are measured in that popular computer term - bits. The ones you're most likely to come across are 40 bit, 56 bit, 128 bit, and more recently 256 and 512 bit. On a regular desktop computer, you wouldn't be able to crack any of these within your own lifetime. In fact 128 bit encryption you wouldn't be able to crack within the lifetime of the universe.
Cracking encrypted material
is enormously expensive, so you can assume your messages won't be cracked unless
they're of great value to the security services. All other snoopers, including
hackers and even the police, won't be able to read your encrypted messages.
Make sure you use good passwords. Here are some tips about passwords.
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