David J. Malan

• Harvard University

CS50 is Harvard University's introductory course aimed at majors and non-majors alike. Each week, students complete programming assignments and have traditionally received feedback from staff in the form of comments on PDFs of their code. Staff have historically reported spending significant amounts of time grading because of bottlenecks that inclu...

We propose a client-side virtual machine (VM) as an alternative to on-campus clusters and off-campus clouds as a development environment for students in introductory courses. In Fall 2011, we deployed the CS50 Appliance, our own such VM, to 600 students on campus and, in Fall 2012, to 700 students on campus and 140,000 students online. We present i...

Distance education is by no means new. Indeed, long before the Internet came along were universities making educational content available to students off campus via VHS, CD-ROM, and other media. But what is new is the scale on which universities and, in some cases, individual faculty are now operating. Massive open online courses (otherwise known a...

CS50 is Harvard's introductory course for majors and non-majors alike. For years, we have posted videos of the course's lectures and sections online for the sake of review and distance education alike. But students' experience with these videos has been historically passive. Students have been able to watch the course's content on demand, rewinding...

In his SIGCSE 2007 keynote, Grady Booch exhorted us to share the "passion, beauty, joy and awe" (PBJA) of computing. This led to sessions that have provided a forum for sharing: What we've done: Highlighting successful PBJA initiatives the presenters have undertaken or seen and wish to trumpet; What we should do (curriculum): Pointing out where our...

Every time I re-use a handout, I look it over and make a few little "improvements". I play around with code demos and entertain myself with different slide transitions. However, inevitably, I return to the conclusion that most of what my students learn in my course comes from the assignments. Great assignments are hard to dream up and time-consumin...

We introduce CS50 Sandbox, an environment for secure execution of untrusted code. Implemented as an asynchronous HTTP server, CS50 Sandbox offers clients the ability to execute programs (both interactive and non-interactive) written in any compiled or interpreted language in a tightly controlled, resource-constrained environment. CS50 Sandbox's HTT...

I worry over topics for the syllabus, fretting over demos and presentations. And yet, I always come back to the fact that most of what my students learn and remember from my course comes from the assignments. Great assignments are hard to dream up and time-consuming to develop. With that in mind, the Nifty Assignments session is all about promoting...

Research on swarming has primarily focused on applying swarming behavior with physics-derived or ad-hoc models to tasks requiring collective intelligence in robotics and optimization. In contrast, applications in signal processing are still lacking. The purpose of this paper is to investigate the use of biologically-inspired swarm methods for signa...

In this talk, I'll explore some of the ways educators share details of their practice and of how they find out "what works" from others. This exploration will include examining some barriers and inhibitors to successful exchange and some thoughts on ...

Computer Science 50 is Harvard College’s introductory course for majors and non-majors alike, enrollment in which both rose and fell along with the dotcoms. Although enrollment peaked in 1996 at 386 students, it had settled by 2002 in the neighborhood of 100. We set out in 2007 to combat that trend by tackling two problems. We hypothesized that CS5...

In Fall 2008, we moved Harvard College’s introductory computer science course, CS50, into the cloud. Rather than continue to rely on our own instructional computing infrastructure on campus, we created a load-balanced cluster of virtual machines (VMs) for our 330 students within Amazon Elastic Compute Cloud (EC2). Our goals were both technical and...

In Fall 2007, we introduced “virtual office hours” into Harvard College’s introductory computer science course, CS 50, so that students could meet with teaching fellows (TFs) online to discuss problem sets at any hour from anywhere. Our goals were to lower the bar to interaction among TFs and students and to improve the efficiency and convenience o...

Over the last 45 years as a student and faculty member in Computer Science, I have been involved in learning, teaching, and writing for the CS1 course. I have authored or co-authored textbooks for CS1 in nine different programming languages from Fortran ...

CS 50 is Harvard College’s introduction to Computer Science for majors and non-majors alike. Each week, our 330 students submit programming assignments comprising hundreds of lines of code that must then be graded. Although we can assess the correctness of some code automatically, some measures of quality require human attention. In Fall 2008, we e...

We present a critical evaluation of the first known implementation of elliptic curve cryptography over F 2 p for sensor networks based on the 8-bit, 7.3828-MHz MICA2 mote. We offer, along the way, a primer for those interested in the field of cryptography for sensor networks. We discuss, in particular, the decisions underlying our design and altern...

Scratch is a "media-rich programming environment" recently developed by MIT's Media Lab that "lets you create your own animations, games, and interactive art." Although Scratch is intended to "enhance the development of technological fluency [among youths] at after-school centers in economically disadvantaged communities," we find rarkable potentia...

In recent months [teachers have] become publishers of content and students subscribers thereof by way of podcasts, feeds of audio, video, and other content that can be downloaded to clients like iTunes and devices like iPods. In the fall of 2005, we ourselves began to podcast Harvard Extension School's Computer Science E-1 in both audio and video f...

The speed of today’s worms demands automated detection, but the risk of false positives poses a difficult problem. In prior work, we proposed a host-based intrusion-detection system for worms that leveraged collaboration among peers to lower its risk of false positives, and we simulated this approach for a system with two peers. In this paper, we b...

Many of today’s privacy-preserving tools create a big file that fills up a hard drive or USB storage device in an effort to overwrite all of the “deleted files” that the media contain. But while this technique is widespread, it is largely unvalidated. We evaluate the effectiveness of the “big file technique” using sector-by-sector disk imaging on f...

This paper describes the Advanced Forensic Format (AFF), which is designed as an alternative to current proprietary disk image formats. AFF offers two significant benefits. First, it is more flexible because it allows extensive metadata to be stored with images. Second, AFF images consume less disk space than images in other formats (e.g., En-Case...

This paper describes the Advanced Forensic Format (AFF), which is designed as an alternative to current proprietary disk image formats. AFF offers two significant benefits. First, it is more flexible because it allows extensive metadata to be stored with images. Second, AFF images consume less disk space than images in other formats (e.g., EnCase i...

We propose a host-based, runtime defense against worms that achieves negligible risk of false positives through peer-to-peer cooperation. We view correlation among otherwise independent peers’ behavior as anomalous behavior, indication of a fast-spreading worm. We detect correlation by exploiting worms’ temporal consistency, similarity (low tempora...

We present the first known implementation of elliptic curve cryptography over F_2p for sensor networks based on the 8-bit, 7.3828-MHz MICA2 mote. Through instrumentation of UC Berkeley's TinySec module, we argue that, although secret-key cryptography has been tractable in this domain for some time, there has remained a need for an efficie...

Sensor networks, a new class of devices has the potential to revolutionize the capture, processing, and communication of critical data for use by first responders. CodeBlue integrates sensor nodes and other wireless devices into a disaster response setting and provides facilities for ad hoc network formation, resource naming and discovery, security...

Current distributed sensor network platforms lack comprehensive lowpower routing techniques and efficient public key cryptography mechanisms. Reducing power for individual radio transmissions has not been explored sufficiently. Popular sensor node platforms do not include a mechanism for distributing and redistributing shared cryptographic keys amo...

This work explores weaknesses in the W3C's prescription for the serialization and navigation of XML and offers novel remedies through summary structures.

This work presents the first known implementation of elliptic curve cryptography for sensor networks, motivated by those networks' need for an effcient, secure mechanism for shared cryptographic keys' distribution and redistribution among nodes. Through instrumentation of UC Berkeley's TinyOS, this work demonstrates that secret-key cryptography is...

Sensor devices integrating embedded processors, low-power, low-bandwidth radios, and a modest amount of storage have the potential to enhance emergency medical care. Wearable vital sign sensors can track patient status and location, while simultaneously operating as active tags. We introduce CodeBlue, a wireless infrastructure intended for deployme...

Botnets allow adversaries to wage attacks on unprecedented scales at unprecedented rates, motivation for which is no longer just malice but profits instead. The longer botnets go undetected, the higher those profits. I present in this thesis an architecture that leverages collaborative networks of peers in order to detect bots across the same. Not on...