I wasn't too worried about getting caught doing this, because I had good crypto on my side. Crypto is cryptography, or "secret writing," and it's been around since Roman times (literally: Augustus Caesar was a big fan and liked to invent his own codes, some of which we use today for scrambling joke punchlines in email).
Crypto is math. Hard math. I'm not going to try to explain it in detail because I don't have the math to really get my head around it, either -- look it up on Wikipedia if you really want.
But here's the Cliff's Notes version: Some kinds of mathematical functions are really easy to do in one direction and really hard to do in the other direction. It's easy to multiply two big prime numbers together and make a giant number. It's really, really hard to take any given giant number and figure out which primes multiply together to give you that number.
That means that if you can come up with a way of scrambling something based on multiplying large primes, unscrambling it without knowing those primes will be hard. Wicked hard. Like, a trillion years of all the computers ever invented working 24/7 won't be able to do it.
There are four parts to any crypto message: the original message, called the "cleartext." The scrambled message, called the "ciphertext." The scrambling system, called the "cipher." And finally there's the key: secret stuff you feed into the cipher along with the cleartext to make ciphertext.
It used to be that crypto people tried to keep all of this a secret. Every agency and government had its own ciphers and its own keys. The Nazis and the Allies didn't want the other guys to know how they scrambled their messages, let alone the keys that they could use to descramble them. That sounds like a good idea, right?
Wrong.
The first time anyone told me about all this prime factoring stuff, I immediately said, "No way, that's BS. I mean, sure it's hard to do this prime factorization stuff, whatever you say it is. But it used to be impossible to fly or go to the moon or get a hard-drive with more than a few kilobytes of storage. Someone must have invented a way of descrambling the messages." I had visions of a hollow mountain full of National Security Agency mathematicians reading every email in the world and snickering.
In fact, that's pretty much what happened during World War II. That's the reason that life isn't more like Castle Wolfenstein, where I've spent many days hunting Nazis.
The thing is, ciphers are hard to keep secret. There's a lot of math that goes into one, and if they're widely used, then everyone who uses them has to keep them a secret too, and if someone changes sides, you have to find a new cipher.