This makes regulating cyberspace difficult. A famous New Yorker cartoon of a few years ago illustrated the problem well: Two dogs are sitting at a computer terminal, one saying to the other, On the Internet, nobody knows you're a dog.

The government has been struggling with the Internet's dog problem for some time. Depending on the context, it has offered different responses. Some have been promising if you're a regulator. But these promising responses pose great threats to both privacy and free speech.

Consider the problem of gambling. Gambling is legal in some places and illegal in others. The law generally deals with this difference by permitting those in a gambling-permissive state to call to (and gamble in) another gambling-permissive state. In cyberspace, however, knowing where someone is calling from is tough. Most proposals in Congress aim simply to ban Internet gambling. It's difficult to know who is who. It's too hard to regulate, so behavior that would be legal off the Net is banned on the Net.

Pornography - or, more precisely, sexually explicit speech deemed harmful to minors - is a different story. The constitution guarantees adults access to porn; it permits governments to ban access by kids. But knowing who's a kid is also tough. Recent proposals require that servers block access to porn unless the person accessing it can prove that he or she is an adult. An adult ID would suffice. So would a credit card, which creates the perverse requirement that one expose oneself financially to pornographers before gaining access to constitutionally protected speech. Admittedly, this is less restrictive than gambling's ban, but in constitutional terms it remains a significant burden nonetheless.

Taxes will also be treated differently. The sales tax you pay depends on where you come from when you buy. Again, in cyberspace, your location is difficult to show. But the government is beginning to be creative. The Clinton administration, through Internet policy maven Ira Magaziner, is now oating the idea of using digital certificates to certify your residence. Certificates would sit on your machine, enabling vendors to determine automatically how much tax to charge.

This idea for solving the Internet's dog problem is by far the most effective and potentially the least burdensome. (It's also a potential solution to the gambling and porn problems, but no one is advancing it in those areas.) In principle, once such a certificate is deposited in a browser, a server could check it automatically (no passwords to remember).