Transparency is the New Privacy: Blockchain's Challenge for the Fourth Amendment

Abstract

Blockchain technology is now hitting the mainstream. With the advent of enterprise blockchains, smart contracts, and corporate cryptocurrencies, countless human interactions, legitimate and illegitimate, are being and will be recorded permanently — and visibly — into distributed digital ledgers. Mass surveillance of day-to-day transactions will never have been easier. This article is the first to analyze blockchain protocols within the Fourth Amendment framework. Blockchain’s open, shared digital architecture challenges us to reassess two core premises of modern Fourth Amendment doctrine: that a “reasonable expectation of privacy” upholds the Amendment’s promise of a right to be “secure” against “unreasonable searches,” and that “a reasonable expectation of privacy” is tantamount to total secrecy. The article argues that these current doctrines rest on physical-world analogies that do not hold in blockchain’s unique digital space. Blockchain’s architecture particularly unsettles the physical-world rationales that underpin received Fourth Amendment distinctions such as public/non-public and content/non-content, as well as the third-party and false friend doctrines. Instead, this article argues that blockchain can create security against unreasonable searches, within the Amendment’s meaning, even for data that are shared or public. The key is control, not secrecy. The article weaves together a focused technical analysis of blockchain’s architecture and a careful assessment of current Fourth Amendment jurisprudence and historical context. It builds on scholarly critiques of current Fourth Amendment doctrine, and reveals the surprising connections between blockchain’s philosophical goals and Fourth Amendment theory, showing that blockchain’s open distributed architecture does the work in digital space that privacy does in the physical world to advance Fourth Amendment values such as security, control of information, expression, and personal autonomy. The article also evaluates textualist approaches to blockchain, concluding that blockchain data are an “effect,” subject to trespassory searches under the Supreme Court’s rubric in United States v. Jones. Finally, the article proposes an analytical framework for Fourth Amendment protections for distributed ledgers — corresponding to the levels to which blockchain users evince control of their data — that is grounded in text and theory and that is administratively practicable for courts.