Hsu-Chun Hsiao

SCION: Scalability, Control, and Isolation on Next-Generation Networks

We present the first Internet architecture designed to provide route control, failure isolation, and explicit trust information for end-to-end communications. SCION separates ASes into groups of independent routing sub-planes, called trust domains, which then interconnect to form complete routes. Trust domains provide natural isolation of routing failures and human misconfiguration, give endpoints strong control for both inbound and outbound traffic, provide meaningful and enforceable trust, and enable scalable routing updates with high path freshness. As a result, our architecture provides strong resilience and security properties as an intrinsic consequence of good design principles, avoiding piecemeal add-on protocols as security patches. Meanwhile, SCION only assumes that a few top-tier ISPs in the trust domain are trusted for providing reliable end-to-end communications, thus achieving a small Trusted Computing Base. Both our security analysis and evaluation results show that SCION naturally prevents numerous attacks and provides a high level of resilience, scalability, control, and isolation.

Flooding-resilient broadcast authentication for VANETs

Digital signatures are one of the fundamental security primitives in Vehicular Ad-Hoc Networks (VANETs) because they provide authenticity and non-repudiation in broadcast communication. However, the current broadcast authentication standard in VANETs is vulnerable to signature flooding: excessive signature verification requests that exhaust the computational resources of victims. In this paper, we propose two efficient broadcast authentication schemes, Fast Authentication (FastAuth) and Selective Authentication (SelAuth), as two countermeasures to signature flooding. FastAuth secures periodic single-hop beacon messages. By exploiting the senders ability to predict its own future beacons, FastAuth enables 50 times faster verification than previous mechanisms using the Elliptic Curve Digital Signature Algorithm. SelAuth secures multi-hop applications in which a bogus signature may spread out quickly and impact a significant number of vehicles. SelAuth pro- vides fast isolation of malicious senders, even under a dynamic topology, while consuming only 15%--30% of the computational resources compared to other schemes. We provide both analytical and experimental evaluations based on real traffic traces and NS-2 simulations. With the near-term deployment plans of VANET on all vehicles, our approaches can make VANETs practical.

LAP: Lightweight Anonymity and Privacy

Popular anonymous communication systems often require sending packets through a sequence of relays on dilated paths for strong anonymity protection. As a result, increased end-to-end latency renders such systems inadequate for the majority of Internet users who seek an intermediate level of anonymity protection while using latency-sensitive applications, such as Web applications. This paper serves to bridge the gap between communication systems that provide strong anonymity protection but with intolerable latency and non-anonymous communication systems by considering a new design space for the setting. More specifically, we explore how to achieve near-optimal latency while achieving an intermediate level of anonymity with a weaker yet practical adversary model (i.e., protecting an end-hosts identity and location from servers) such that users can choose between the level of anonymity and usability. We propose Lightweight Anonymity and Privacy (LAP), an efficient network-based solution featuring lightweight path establishment and stateless communication, by concealing an end-hosts topological location to enhance anonymity against remote tracking. To show practicality, we demonstrate that LAP can work on top of the current Internet and proposed future Internet architectures.

A Study of User-Friendly Hash Comparison Schemes

Several security protocols require a human to compare two hash values to ensure successful completion. When the hash values are represented as long sequences of numbers, humans may make a mistake or require significant time and patience to accurately compare the hash values. To improve usability during comparison, a number of researchers have proposed various hash representations that use words, sentences, or images rather than numbers. This is the first work to perform a comparative study of these hash comparison schemes to determine which scheme allows the fastest and most accurate comparison. To evaluate the schemes, we performed an online user study with more than 400 participants. Our findings indicate that only a small number of schemes allow quick and accurate comparison across a wide range of subjects from varying backgrounds.

Policy-based secure deletion

Securely deleting data from storage systems has become difficult today. Most storage space is provided as a virtual resource and traverses many layers between the user and the actual physical storage medium. Operations to properly erase data and wipe out all its traces are typically not foreseen, particularly not in networked and cloud-storage systems. This paper introduces a general cryptographic model for policy-based secure deletion of data in storage systems, whose security relies on the proper erasure of cryptographic keys. Deletion operations are expressed in terms of a policy that describes data destruction through deletion attributes and protection classes. The policy links attributes as specified in deletion operations to the protection class(es) that must be erased accordingly. A cryptographic construction is presented for deletion policies given by directed acyclic graphs; it is built in a modular way from exploiting that secure deletion schemes may be composed with each other. The model and the construction unify and generalize all previous encryption-based techniques for secure deletion. Finally, the paper describes a prototype implementation of a Linux filesystem with policy-based secure deletion.

Efficient and secure threshold-based event validation for VANETs

Determining whether the number of vehicles reporting an event is above a threshold is an important mechanism for VANETs, because many applications rely on a threshold number of notifications to reach agreement among vehicles, to determine the validity of an event, or to prevent the abuse of emergency alarms. We present the first efficient and secure threshold-based event validation protocol for VANETs. Quite counter-intuitively, we found that the z-smallest approach [3] offers the best tradeoff between security and efficiency since other approaches perform better for probabilistic counting. Analysis and simulation shows that our protocol provides > 99% accuracy despite the presence of attackers, collection and distribution of alerts in less than 1 second, and negligible impact on network performance.

SIBRA: Scalable Internet Bandwidth Reservation Architecture

This paper proposes a Scalable Internet Bandwidth Reservation Architecture (SIBRA) as a new approach against DDoS attacks, which, until now, continue to be a menace on todays Internet. SIBRA provides scalable inter-domain resource allocations and botnet-size independence, an important property to realize why previous defense approaches are insufficient. Botnet-size independence enables two end hosts to set up communication regardless of the size of distributed botnets in any Autonomous System in the Internet. SIBRA thus ends the arms race between DDoS attackers and defenders. Furthermore, SIBRA is based on purely stateless operations for reservation renewal, flow monitoring, and policing, resulting in highly efficient router operation, which is demonstrated with a full implementation. Finally, SIBRA supports Dynamic Interdomain Leased Lines (DILLs), offering new business opportunities for ISPs.

STRIDE: sanctuary trail -- refuge from internet DDoS entrapment

We propose STRIDE, a new DDoS-resilient Internet architecture that isolates attack traffic through viable bandwidth allocation, preventing a botnet from crowding out legitimate flows. This new architecture presents several novel concepts including tree-based bandwidth allocation and long-term static paths with guaranteed bandwidth. In concert, these mechanisms provide domain-based bandwidth guarantees within a trust domain - administrative domains grouped within a legal jurisdiction with enforceable accountability; each administrative domain in the trust domain can then internally split such guarantees among its endhosts to provide (1) connection establishment with high probability, and (2) precise bandwidth guarantees for established flows, regardless of the size or distribution of the botnet outside the source and the destination domains. Moreover, STRIDE maintains no per-flow state on backbone routers and requires no key establishment across administrative domains. We demonstrate that STRIDE achieves these DDoS defense properties through formal analysis and simulation. We also show that STRIDE mitigates emerging DDoS threats such as Denial-of-Capability (DoC) [6] and N2 attacks [22] based on these properties that none of the existing DDoS defense mechanisms can achieve.

Efficient Large Flow Detection over Arbitrary Windows: An Algorithm Exact Outside an Ambiguity Region

Many networking and security applications can benefit from exact detection of large flows over arbitrary windows (i.e. any possible time window). Existing large flow detectors that only check the average throughput over certain time period cannot detect bursty flows and are therefore easily fooled by attackers. However, no scalable approaches provide exact classification in one pass. To address this challenge, we consider a new model of exactness outside an ambiguity region, which is defined to be a range of bandwidths below a high-bandwidth threshold and above a low-bandwidth threshold. Given this new model, we propose a deterministic algorithm, EARDet, that detects all large flows (including bursty flows) and avoids false accusation against any small flows, regardless of the input traffic distribution. EARDet monitors flows over arbitrary time windows and is built on a frequent items finding algorithm based on average frequency. Despite its strong properties, EARDet has low storage overhead regardless of input traffic and is surprisingly scalable because it focuses on accurate classification of large flows and small flows only. Our evaluations confirm that existing approaches suffer from high error rates (e.g., misclassifying 1% of small flows as large flows) in the presence of large flows and bursty flows, whereas EARDet can accurately detect both at gigabit line rate using a small amount of memory that fits into on-chip SRAM.

Secure Distributed Data Aggregation

We present a survey of the various families of approaches to secure aggregation in distributed networks such as sensor networks. In our survey, we focus on the important algorithmic features of each approach, and provide an overview of a family of secure aggregation protocols which use resilient distributed estimation to retrieve an approximate query result that is guaranteed to be resistant against malicious tampering; we then cover a second family, the commitment-based techniques, in which the query result is exact but the chances of detecting malicious computation tampering is probabilistic. Finally, we describe a hash-tree based approach that can both give an exact query result and is fully resistant against malicious computation tampering.