Network Security 2022

https://docs.google.com/document/d/1o-jK86y2TBq7EertOeVWDklYS6AvnFY48XGNokaH3OQ/edi

Network Security 2021 Syllabus

https://docs.google.com/document/d/1kHYHxSV_i5IMp0DwQK6DflQB_0s9-9iCMr6hDsIfUu8/edi

New Applications Of Public Ledgers

The last decade and a half has seen the rise of a new class of systems loosely categorized as public ledgers. Public ledgers guarantee that all posted information is permanently available to the entire public. Common realizations of public ledgers include public blockchains and centralized logs. In this work we investigate novel applications of public ledgers. We begin by describing enclave ledger interaction, a computational method that allows the execution of trusted execution environments or cryptographically obfuscated programs to be conditioned on the contents of the ledger. We then show how this conditional execution paradigm can be used to achieve fairness in dishonest majority secure multiparty computation, which is impossible in the plain model. Finally, we show how conditional execution can be used to build systems that facilitate law enforcement access to ciphertext while ensuring robust transparency and accountability mechanisms

Efficient proofs of software exploitability for real-world processors

CRAhttps://eprint.iacr.org/2022/1223.pdfPublished versio

Pulsar: Secure Steganography through Diffusion Models

Widespread efforts to subvert acccess to strong cryptography has renewed interest in steganography, the practice of embedding sensitive messages in mundane cover messages. Recent efforts at provably secure steganography have only focused on text-based generative models and cannot support other types of models, such as diffusion models, which are used for high-quality image synthesis. In this work, we initiate the study of securely embedding steganographic messages into the output of image diffusion models. We identify that the use of variance noise during image generation provides a suitable steganographic channel. We develop our construction, Pulsar, by building optimizations to make this channel practical for communication. Our implementation of Pulsar is capable of embedding $\approx 275$-$542$ bytes (on average) into a single image without altering the distribution of the generated image, all in the span of $\approx 3$ seconds of online time on a laptop. In addition, we discuss how the results of Pulsar can inform future research into diffusion models. Pulsar shows that diffusion models are a promising medium for steganography and censorship resistance

Abuse Resistant Law Enforcement Access Systems

The increasing deployment of end-to-end encrypted communications services has ignited a debate between technology firms and law enforcement agencies over the need for lawful access to encrypted communications. Unfortunately, existing solutions to this problem suffer from serious technical risks, such as the possibility of operator abuse and theft of escrow key material. In this work we investigate the problem of constructing law enforcement access systems that mitigate the possibility of unauthorized surveillance. We first define a set of desirable properties for an abuse-resistant law enforcement access system (ARLEAS), and motivate each of these properties. We then formalize these definitions in the Universal Composability framework, and present two main constructions that realize this definition. The first construction enables prospective access, allowing surveillance only if encryption occurs after a warrant has been issued and activated. The second, more powerful construction, allows retrospective access to communications that occurred prior to a warrant\u27s issuance. To illustrate the technical challenge of constructing the latter type of protocol, we conclude by investigating the minimal assumptions required to realize these systems

Order-C Secure Multiparty Computation for Highly Repetitive Circuits

Running secure multiparty computation (MPC) protocols with hundreds or thousands of players would allow leveraging large volunteer networks (such as blockchains and Tor) and help justify honest majority assumptions. However, most existing protocols have at least a linear (multiplicative)dependence on the number of players, making scaling difficult. Known protocols with asymptotic efficiency independent of the number of parties (excluding additive factors) require expensive circuit transformations that induce large overheads. We observe that the circuits used in many important applications of MPC such as training algorithms used to create machine learning models have a highly repetitive structure. We formalize this class of circuits and propose an MPC protocol that achieves O(|C|) total complexity for this class. We implement our protocol and show that it is practical and outperforms O(n|C|) protocols for modest numbers of players

Efficient Set Membership Proofs using MPC-in-the-Head

Set membership proofs are an invaluable part of privacy preserving systems. These proofs allow a prover to demonstrate knowledge of a witness $w$ corresponding to a secret element $x$ of a public set, such that they jointly satisfy a given NP relation, {\em i.e.} $\mathcal{R}(w,x)=1$ and $x$ is a member of a public set $\{x_1, \ldots, x_\ell\}$. This allows the identity of the prover to remain hidden, eg. ring signatures and confidential transactions in cryptocurrencies. In this work, we develop a new technique for efficiently adding logarithmic-sized set membership proofs to any MPC-in-the-head based zero-knowledge protocol (Ishai et al. [STOC\u2707]). We integrate our technique into an open source implementation of the state-of-the-art, post quantum secure zero-knowledge protocol of Katz et al. [CCS\u2718]. We find that using our techniques to construct ring signatures results in signatures (based only on symmetric key primitives) that are between 5 and 10 times smaller than state-of-the-art techniques based on the same assumptions. We also show that our techniques can be used to efficiently construct post-quantum secure RingCT from only symmetric key primitives