I have just posted an early paper I wrote that still seems to generate some interest: The Fourth Amendment in Cyberspace: Can Encryption Create a "Reasonable Expectation of Privacy"?, 33 Conn. L. Rev. 503 (2001). (33 pages, .pdf) This was a really fun paper to write, as the argument is highly counterintuitive, sets up lots of fun puzzles, and also ultimately sheds light on important but underappreciated aspects of the Fourth Amendment.

  Here's the abstract:

Does encrypting Internet communications create a reasonable expectation of privacy in their contents, triggering Fourth Amendment protection? At first blush, it seems that the answer must be yes: A reasonable person would surely expect that encrypted communications will remain private. In this paper, Professor Kerr explains why this intuitive answer is entirely wrong: Encrypting communications cannot create a reasonable expectation of privacy. The reason is that the Fourth Amendment regulates access, not understanding: no matter how unlikely it is that the government will successfully decrypt ciphertext, the Fourth Amendment offers no protection if it succeeds. As a result, the government does not need a search warrant to decrypt encrypted communications. This surprising result is consistent with Fourth Amendment caselaw: it matches how courts have resolved cases involving the reassembly of shredded documents, recovery of deleted files, and the translation of foreign languages. The Fourth Amendment may regulate government access to ciphertext, but it does not regulate government efforts to translate ciphertext into plaintext.

  I should add that the broader Fourth Amendment framework I offer in the article (between what I then called "rights-based" and "statistical" approaches) has changed significantly in the last five years. I'm working on a piece now that I think has a much more helpful framework, and also situates the argument of this early effort more accurately. Despite that, though, I still think the argument in this early article is correct.