There are actually some numbers that, in the US at least, you could be committing a crime just by having in your possession. This all centers around digital security and copyright protection. Much of digital security these days builds off of the properties of prime numbers – numbers that can only be divided by themselves and 1. The way security keys often work is that they take two prime numbers and multiply them together, giving a larger result. It’s relatively simple to simply take two primes and figure out what they multiply two. It is *much* less simple to take that result and try to determine which two primes are the factors of that number.

The difficulty in actually finding and verifying prime numbers makes it a very secure format – for now at least. In fact, it’s so difficult to find new prime numbers on the scale they are used, that organizations like the Electronic Frontier Foundation will pay as much as $250,000 for new prime numbers. And these are really, really massive numbers. The largest known prime so far is 2 to the 74,207,281st power, minus 1. That’s a gigantic prime.

Where you can land in trouble is that some of these numbers are used to unlock things such as digital security for DVD copy protection. Possession of the proper “key” prime would allow you to freely duplicate the movies. Since the Digital Millennium Copyright Act forbids ownership of any tools that can be used to bypass copy protected systems, this key number can be considered one such tool, and could land you in hot water.

Cryptology and digital security has always been interesting to me, but the more I read in depth into how this stuff works, the more it goes over my head.

[*via* IFL Science]