Koh considers everything that passes across the Internet -- e-mail, mailing list postings, Web pages -- as no more private than postcards that can be read by anyone along their path. That realization long ago inspired an epiphany for the Northwestern University network engineer: "I was really amazed at the ease with which my network traffic could be intercepted and examined, even with no malicious intent whatsoever."

It wasn't a question of Koh having secrets. There are just some things that are no one else's business. So for the past five years, both at work and at home, he has used PGP to routinely encrypt potentially sensitive communication, turning ordinary data into bits and bytes of meaningless gibberish readable only by those with the proper digital key.

"Typically, I [digitally] sign most of my outgoing messages, and several people and organizations with whom I correspond regularly also require encryption of messages," he says.

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