On first reading, this Second Circuit decision in Church of the American Knights of the Ku Klux Klan V. Kerik is pretty awful.
It's not just that the court seems to have outlawed Halloween. No, it's that the precedent is just waiting to be used to block the operation of anonymous remails and the use of strong cryptography.
As we move to a world of mandatory ID cards and inescapable facial recognition, not to mention lie-detector specs, this case could really come back to, um, haunt us.
I discuss the general issues in two papers, Anonymity in the Balance (book chapter in Digital Anonymity: Tensions and Dimensions (C. Nicoll, J.E.J. Prins & M.J.M. van Dellen eds. 2003), and The Death of Privacy?, 52 Stan. L. Rev. 1461 (2000).
The more specific issue of the legal rules relating to strong crypto is discussed in the only very slightly dated The Metaphor is the Key: Cryptography, the Clipper Chip and the Constitution, 143 U. Penn. L. Rev. 709 (1995). You can also skip straight to my discussion of the earlier mask law cases.
Update: For those who don't want to load the slow .pdf case file, I should perhaps explain that the Second Circuit upheld New York's anti-mask law against a group of constitutional challenges—although it dodged one of the key issues, the extent to which a right to speak annonymously was implicated. The court was able to do this by making the scarecely-credible assertion that the right to protect one's associations (NAACP v. Alabama) was not implicated when demonstrators were forced to expose their faces as a condition of appearing in public—in this case at a public demonstration. The court also rejected as irrelevant the claim that this would discourage attendence at KKK rallies, but the argument it uses seems too broad.
Assuming for the discussion that New York's anti-mask law makes some members of the American Knights less willing to participate in rallies, we nonetheless reject the view that the First Amendment is implicated every time a law makes someone—including a member of a politically unpopular group—less willing to exercise his or her free speech rights. While the First Amendment protects the rights of citizens to express their viewpoints, however unpopular, it does not guarantee ideal conditions for doing so, since the individual's right to speech must always be balanced against the state's interest in safety, and its right to regulate conduct that it legitimately considers potentially dangerous.
It seems to me that had this logic been applied to NAACP v. Alabama that case would have gone the other way, and there would be much weaker protection for anonymous speech and association.