Public Accountability vs. Secret Laws: Can They Coexist?: A Cryptographic Proposal

Abstract

“Our Laws are not generally known; they are kept secret by the small group of nobles who rule us. We are convinced that these ancient laws are scrupulously administered; nevertheless it is an extremely painful thing to be ruled by laws that one does not know.” —Franz Kafka, Parables and Paradoxes. Post 9/11, journalists, scholars and activists have pointed out that it secret laws - a body of law whose details and sometime mere existence is classified as top secret - were on the rise in all three branches of the US government due to growing national security concerns. Amid heated current debates on governmental wishes for exceptional access to encrypted digital data, one of the key issues is: which mechanisms can be put in place to ensure that government agencies follow agreed-upon rules in a manner which does not compromise national security objectives? This promises to be especially challenging when the rules, according to which access to encrypted data is granted, may themselves be secret.

In this work we show how the use of cryptographic protocols, and in particular, the idea of zero knowledge proofs can ensure accountability and transperancy of the government in this extraordinary, seemingly deadlocked, setting. We propose an efficient record-keeping infrastructure with versatile publicly verifiable audits that preserve (information-theoretic) privacy of record contents as well as of the rules by which the records are attested to abide. Our protocol is based on existing blockchain and cryptographic tools including commitments and zero-knowledge SNARKs, and satisfies the properties of indelibility (i.e., no back-dating), perfect data privacy, public auditability of secret data with secret laws, accountable deletion, and succinctness. We also propose a variant scheme where entities can be required to pay fees based on record contents (e.g., for violating regulations) while still preserving privacy. Our scheme can be directly instantiated on the Ethereum blockchain (and a simplified version with weaker guarantees can be instantiated with Bitcoin).