NSEC5: Provably Preventing DNSSEC Zone Enumeration
Download: Paper (PDF)
Date: 7 Feb 2015
Document Type: Briefing Papers
Additional Documents: Slides
Associated Event: NDSS Symposium 2015
This paper uses cryptographic techniques to study the problem of zone enumeration in DNSSEC. DNSSEC is designed to prevent network attackers from tampering with domain name system (DNS) messages. The cryptographic machinery used in DNSSEC, however, also creates a new vulnerability, zone enumeration, enabling an adversary to use a small number of online DNSSEC queries combined with offline dictionary attacks to learn which domain names are present or absent in a DNS zone. We prove that the design underlying current DNSSEC standard, with NSEC and NSEC3 records, inherently suffers from zone enumeration: specifically, we show that security against network attackers and privacy against zone enumeration cannot be satisfied simultaneously unless the DNSSEC server performs online public-key cryptographic operations. We then propose NSEC5, a new cryptographic construction that solves the problem of DNSSEC zone enumeration while remaining faithful to the operational realities of DNSSEC. NSEC5 can be thought of as a variant of NSEC3 in which an the unkeyed hash function is replaced with an RSA-based keyed hashing scheme.