Pretty Good Privacy
is military grade cryptographic software. Even governments with supercomputers can't break it. There are versions for Win, Mac, various flavors of Unix, Amiga, and many other platforms.
Here's a song I wrote called Free Speech in Cyberspace
with a bonus dirty picture and open letter to Senator Exon, author of the CDA.
The celebrated libertarians pictured above are (1st row - individualists) John Locke, Thomas Jefferson, Ayn Rand, (2nd row - collectivists) Pierre Proudhon, Michael Bakunin, and Emma Goldman.