In theory, the mechanism could be cheap: The government is even considering giving such certificates away. Once in place, the architecture would make it possible to certify not just where a Web surfer came from, but potentially much more.

It's this much more that presents problems. Digital certificates are tools not only for government, but for e-commerce, as well. The greatest growth in certificate technology is for business transactions, not government regulation. The most ambitious plans for its deployment come from banks, not Congress. We will soon see a certificate-rich Internet, even if government does nothing. Commerce will induce people to hold certificates that identify many facts about them (name, age, residence, sex, profession) and servers will condition access based upon what certificates someone holds.

This is both good news and bad news. The good news, at least for those who oppose the regulation of porn and gambling, is that the very existence of these less burdensome alternatives will mean that the constitution will favor them over more restrictive alternatives.

But it is bad news for those who romanticized the unregulability of the early Internet, and especially for those who fear the privacy threat that this certificate-enabled Internet will present. As certificates become more prevalent, they will make the Net far easier to regulate. And the more certificates reveal about who someone is, the more private data they will put at risk.

No matter what the government does, certificate architecture is probably unavoidable, because businesses need a way to certify with confidence. But certificates could be designed in many ways, and some are more protective of public values than others. It's too soon for government to fix on a technology without subsidizing technologies of yesterday. But government should watch as these certificate architectures develop and ensure that they are built in ways consistent with the values of privacy and anonymity.

Digital ID is in our future. We should make sure it is a future that we want.

Lawrence Lessig is the Berkman Professor of Law at Harvard Law School. E-mail him at lessig@law.harvard.edu.