The Fourth Amendment in Cyberspace: Can Encryption Create a Reasonable Expectation of Privacy?

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.

Keywords: Fourth Amendment, ciphertext, encryption, plaintext, reasonable expectation of privacy

JEL Classification: K14, K39, K42