Simon S. Woo

Prioritized LT codes

It is common in data transmissions that some information is more important than others. This is especially true in space communications where mission critical information or science data are high priority. In this work, we propose a simple yet constructive scheme to send high priority data reliably and efficiently using Luby transform (LT) codes. The new proposed scheme modifies the conventional LT encoder to send high priority data as a degree 1 and 2 so that high priority data can be quickly resolved and very likely recovered before a decoder stops. Preliminary results show that a carefully designed degree distribution of high priority data increases the likelihood of receiving high priority information while having negligible performance impact on data with lower priority. The performance of the proposed scheme is evaluated and compared with the conventional LT approach with the same parameters under a range of erasure error rates.

Optimal application allocation on multiple public clouds

Abstract Cloud computing customers currently host all of their application components at a single cloud provider. Single-provider hosting eases maintenance tasks, but reduces resilience to failures. Recent research (Li et al., 2010) also shows that providers’ offers differ greatly in performance and price, and no single provider is the best in all service categories. In this paper we investigate the benefits of allocating components of a distributed application on multiple public clouds (multi-cloud). We propose a resource allocation algorithm that minimizes the overall cloud operation cost, while satisfying required service-level agreements (SLAs). In spite of the additional delays for inter-cloud communication and the additional costs for inter-cloud data transfer, our simulation study, using real cloud performance and cost data, demonstrates that multi-cloud allocation outperforms single-cloud allocations in a variety of realistic scenarios.

Space Communications and Navigation (SCaN) Network Simulation Tool Development and Its Use Cases

In this work, we focus on the development of a simulation tool to assist in analysis of current and future (proposed) network architectures for NASA. Specifically, the Space Communications and Navigation (SCaN) Network is being architected as an integrated set of new assets and a federation of upgraded legacy systems. The SCaN architecture for the initial missions for returning humans to the moon and beyond will include the Space Network (SN) and the Near-Earth Network (NEN). In addition to SCaN, the initial mission scenario involves a Crew Exploration Vehicle (CEV), the International Space Station (ISS) and NASA Integrated Services Network (NISN). We call the tool being developed the SCaN Network Integration and Engineering (SCaN NIE (2) to optimize system configurations by testing a larger parameter space than may be feasible in either production networks or an emulated environment; (3) to test solutions in order to find issues/risks before committing more significant resources needed to produce real hardware or flight software systems. We describe two use cases of the tool: (1) standalone simulation of CEV to ISS baseline scenario to determine network performance, (2) participation in Distributed Simulation Integration Laboratory (DSIL) tests to perform function testing and verify interface and interoperability of geographically dispersed simulations/emulations.

Life-experience passwords (LEPs)

Passwords are widely used for user authentication, but they are often difficult for a user to recall, easily cracked by automated programs and heavily reused. Security questions are also used for secondary authentication. They are more memorable than passwords, but are very easily guessed. We propose a new authentication mechanism, called life-experience passwords (LEPs), which outperforms passwords and security questions, both at recall and at security. Each LEP consists of several facts about a user-chosen past experience, such as a trip, a graduation, a wedding, etc. At LEP creation, the system extracts these facts from the users input and transforms them into questions and answers. At authentication, the system prompts the user with questions and matches her answers with the stored ones. In this paper we propose two LEP designs, and evaluate them via user studies. We further compare LEPs to passwords, and find that: (1) LEPs are 30--47 bits stronger than an ideal, randomized, 8-character password, (2) LEPs are up to 3x more memorable, and (3) LEPs are reused half as often as passwords. While both LEPs and security questions use personal experiences for authentication, LEPs use several questions, which are closely tailored to each user. This increases LEP security against guessing attacks. In our evaluation, only 0.7% of LEPs were guessed by friends, while prior research found that friends could guess 17--25% of security questions. LEPs also contained a very small amount of sensitive or fake information. All these qualities make LEPs a promising, new authentication approach.

Analysis of Proximity-1 Space Link Interleaved Time Synchronization (PITS) Protocol

To synchronize clocks between spacecraft in proximity, the Proximity-1 Space Link Interleaved Time Synchronization (PITS) Protocol has been proposed. PITS is based on the NTP Interleaved On-Wire Protocol and is capable of being adapted and integrated into CCSDS Proximity-1 Space Link with minimal modifications. In this work, we discuss the correctness and liveness of PITS. Further, we analyze and evaluate the time synchronization latency performance with various channel error rates in different PITS operational modes.

Good Automatic Authentication Question Generation

We explore a novel application of Question Generation (QG) for authentication use, where questions are widely used to verify user identity for online accounts. In our approach, we prompt users to provide a few sentences about their personal life events. We transform user-provided input sentences into a set of simple fact-based authentication questions. We compared our approach with previous QG systems, and evaluation results show that our approach yielded better performance and the promise of future personalized authentication question generation.

3DOC: 3D object CAPTCHA

Current 2D CAPTCHA mechanisms can be easily defeated by character recognition and segmentation attacks by automated machines. Recently, 3D CAPTCHA schemes have been proposed to overcome the weaknesses of 2D CAPTCHA for a few websites. However, researchers also demonstrate the offline pre-processing techniques to break 3D CAPTCHA. In this work, we propose a novel 3D object based CAPTCHA scheme that projects the CAPTCHA image over a 3D object. We develop the prototype and present the proof-of-concept of 3D object based CAPTCHA scheme to protect websites against automated attacks.

Space network time distribution and synchronization protocol development for Mars proximity link

Time distribution and synchronization in deep space network are challenging due to long propagation delays, spacecraft movements, and relativistic effects. Further, the Network Time Protocol (NTP) designed for terrestrial networks may not work properly in space. In this work, we consider the time distribution protocol based on time message exchanges similar to Network Time Protocol (NTP). We present the Proximity-1 Space Link Interleaved Time Synchronization (PITS) algorithm that can work with the CCSDS Proximity-1 Space Data Link Protocol. The PITS algorithm provides faster time synchronization via two-way time transfer over proximity links, improves scalability as the number of spacecraft increase, lowers storage space requirement for collecting time samples, and is robust against packet loss and duplication which underlying protocol mechanisms provide.

Interfacing Space Communications and Navigation Network Simulation with Distributed System Integration Laboratories (DSIL)

NASA’s planned Lunar missions will involve multiple NASA centers where each participating center has a specific role and specialization. In this vision, the Constellation program (CxP)’s Distributed System Integration Laboratories (DSIL) architecture consist of multiple System Integration Labs (SILs), with simulators, emulators, testlabs and control centers interacting with each other over a broadband network to perform test and verification for mission scenarios. To support the end-to-end simulation and emulation effort of NASA’ exploration initiatives, different NASA centers are interconnected to participate in distributed simulations. Currently, DSIL has interconnections among the following NASA centers: Johnson Space Center (JSC), Kennedy Space Center (KSC), Marshall Space Flight Center (MSFC) and Jet Propulsion Laboratory (JPL). Through interconnections and interactions among different NASA centers, critical resources and data can be shared, while independent simulations can be performed simultaneously at different NASA locations, to effectively utilize the simulation and emulation capabilities at each center. In this work, we describe the specific role and development activities at JPL for Space Communications and Navigation (SCaN) Network simulator using the Multi-mission Advanced Communications Hybrid Environment for Test and Evaluation (MACHETE) tool to simulate communications effects among mission assets. Using MACHETE, different space network configurations among spacecraft and ground systems of various parameter sets can be simulated. Data that is necessary for tracking, navigation, and guidance of spacecraft such as Crew Exploration Vehicle (CEV), Crew Launch Vehicle (CLV), and Lunar Relay Satellite (LRS) are disseminated to different NASA centers and updated periodically using the High Level Architecture (HLA). In addition, mission data are being relayed through SCaN with simulated network effects.

Leveraging Semantic Transformation to Investigate Password Habits and Their Causes

It is no secret that users have difficulty choosing and remembering strong passwords, especially when asked to choose different passwords across different accounts. While research has shed light on password weaknesses and reuse, less is known about user motivations for following bad password practices. Understanding these motivations can help us design better interventions that work with the habits of users and not against them. We present a comprehensive user study in which we both collect and analyze users real passwords and the reasoning behind their password habits. This enables us to contrast the users actual behaviors with their intentions. We find that user intent often mismatches practice, and that this, coupled with some misconceptions and convenience, fosters bad password habits. Our work is the first to show the discrepancy between user intent and practice when creating passwords, and to investigate how users trade off security for memorability.