Network Security 2023

https://docs.google.com/document/d/18SyaJJUBr055WaWQ0LvUHPKfB4ltZDqISJ7ZgIVmeNA

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

Giving State to the Stateless: Augmenting Trustworthy Computation with Ledgers

In this work we investigate the problem of achieving secure computation by combining stateless trusted devices with public ledgers. We consider a hybrid paradigm in which a client-side device (such as a co-processor or trusted enclave) performs secure computation, while interacting with a public ledger via a possibly malicious host computer. We explore both the constructive and potentially destructive implications of such systems. We first show that this combination allows for the construction of stateful interactive functionalities (including general computation) even when the device has no persistent storage; this allows us to build sophisticated applications using inexpensive trusted hardware or even pure cryptographic obfuscation techniques. We further show how to use this paradigm to achieve censorship-resistant communication with a network, even when network communications are mediated by a potentially malicious host. Finally we describe a number of practical applications that can be achieved today. These include the synchronization of private smart contracts; rate limited mandatory logging; strong encrypted backups from weak passwords; enforcing fairness in multi-party computation; and destructive applications such as autonomous ransomware, which allows for payments without an online party

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

Dora: Processor Expressiveness is (Nearly) Free in Zero-Knowledge for RAM Programs

Existing protocols for proving the correct execution of a RAM program in zero-knowledge are plagued by a processor expressiveness trade-off : supporting fewer instructions results in smaller processor circuits (which improves performance), but may result in more program execution steps because non-supported instruction must be emulated over multiple processor steps (which diminishes performance). We present Dora, a concretely efficient zero-knowledge protocol for RAM programs that sidesteps this tension by making it (nearly) free to add additional instructions to the processor. The computational and communication complexity of proving each step of a computation in Dora, is constant in the number of supported instructions. Dora is also highly generic and only assumes the existence of linearly homomorphic commitments. We implement Dora and demonstrate that on commodity hardware it can prove the correct execution of a processor with thousands of instruction, each of which has thousands of gates, in just a few milliseconds per step

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