An integral part of modeling the global view of network security is constructing attack graphs. In practice, attack graphs are produced manually by Red Teams. Construction by hand, however, is tedious, error-prone, and impractical for attack graphs larger than a hundred nodes. In this paper we present an automated technique for generating and analyzing attack graphs. We base our technique on symbolic model checking algorithms, letting us construct attack graphs automatically and efficiently. We also describe two kinds of analysis on attack graphs for helping analysts decide which attacks would be most cost-effective to guard against. We implemented our technique in a tool suite and tested it on a small network example, which includes models of a firewall and intrusion detection system.

Security and Privacy paper. Technical report.

Verifiable Secret Sharing

We present a new protocol for verifiably redistributing secrets from an (m, n) threshold sharing scheme to an (m', n') scheme. Our protocl guards against dynamic adversaries. We observe that existing protocols either cannot be readily extended to allow redistribution between different threshold schemes, or have vulnerabilities that allow faulty old shareholders to distribute invalid shares to new shareholders. Our primary contribution is that in our protocol, new shareholders can verify the validity of their shares after redistribution between different threshold shemes.

Technical report.

Theory Generation

We introduce theory generation, a new general-purpose technique for performing automated verification. Theory generation draws inspiration from, and complements, both automated theorem proving and symbolic model checking, the two approaches that currently dominate mechanical reasoning. At the core of this approach is the notion of producing a finite representation of a theory---all the facts derivable from a set of assumptions. We present an algorithm for producing compact theory representations for an expressive class of simple logics.

Security-sensitive protocols are widely used today, and the growing popularity of electronic commerce is leading to increasing reliance on them. Though simple in structure, these protocols are notoriously difficult to design properly. Since specifications of these protocols typically involve only a small number of principals, keys, nonces, and messages, and since many properties of interest can be expressed in ``little logics'' such as the Burrows, Abadi, and Needham (BAN) logic of authentication, this domain is amenable to theory generation.

Theory generation enables fast, automated analysis of these security protocols. Given the theory representation generated from a protocol specification, one can quickly test for specific desired properties, as well as directly manipulate the representation to perform other kinds of analysis, such as protocol comparison. This paper describes applications of theory generation to more than a dozen security protocols using four different logics of belief; these examples confirm, or in some cases expose flaws in earlier analyses.

Journal submission.