Based on the advances in laptop technologies and the mobility characteristics, laptops have become a vital device used at various places. Usually, numerous sensitive files such as credit card numbers and Web cookies are stored on laptops for convenient usage. However, if a laptop is stolen, the data stored on it is easily leaked; which may cause serious consequences. Encrypting files by encryption keys is a general solution; however, if the decryption keys are also stored on laptops, the files can also be decrypted by adversaries easily. To solve this problem, this paper proposes the Mobile Encryption for Laptop data Protection (MELP) system. MELP includes the design of an online server and mobile phone, and encrypts each sensitive file by a file system encryption key, which is further sequentially encrypted twice by the phone's and server's encryption keys. The reason of adopting a mobile phone is that at least one simple confirmation of execution must be performed by a user, and the reason of adopting an online server is that if both user's laptop and mobile phone are stolen, users can still disable the online decryption process on the server.

As the capabilities of smartphones increase, users are beginning to rely on these mobile and ubiquitous platforms to perform more tasks. In addition to traditional computing tasks, people are beginning to use smartphones to interact with people they meet. Often this interaction begins with an exchange, e.g., of cryptographic keys. Hence, a number of protocols have been developed to facilitate this exchange. Unfortunately, those protocols that provide strong security guarantees often suffer from usability problems, and easy-to-use protocols may lack the desired security guarantees.

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 sender's 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.

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.

Data breaches due to stolen laptops are a major problem. Solutions exist to secure sensitive files on laptops, but are rarely deployed because users view them as inconvenient. This work examines how to provide an unobtrusive system to securely encrypt files on laptops. We observe that only a fraction of users' files contain sensitive information. In addition, the majority of users' accesses to these sensitive files occur while in a trusted location that malicious parties are unable to access. Rather than protecting all of the user's files, we secure user designated sensitive files that are rarely accessed outside of specified trusted locations. Our approach is to use information and services available only in a trusted location to assist in key derivation without user involvement and without authenticating the laptop to any outside service. We study two settings: home use where zero management overhead is needed (i.e., a plug-and-play solution) and a corporate setting where staff management of a whitelist of acceptable devices allows a higher level of security. We have implemented both systems and found automatic key derivation introduces a five second delay during the initial access to sensitive files.

Establishing trust between a group of individuals remains a difficult problem. Prior works assume trusted infrastructure, require an individual to trust unknown entities, or provide relatively low probabilistic guarantees of authenticity (95 percent for realistic settings). This work presents SPATE, a primitive that allows users to establish trust via mobile devices and physical interaction. Once the SPATE protocol runs to completion, its participants' mobile devices have authentic data that their applications can use to interact securely (i.e., the probability of a successful attack is 2-24). For this work, we leverage SPATE as part of a larger system to facilitate efficient, secure, and user-friendly collaboration via e-mail, file-sharing, and text messaging services. Our implementation of SPATE on Nokia N70 smartphones allows users to establish trust in small groups of up to eight users in less than one minute. The example SPATE applications provide increased security with little overhead noticeable to users once keys are established.

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.

Establishing trust between a group of individuals remains a difficult problem. Prior works assume trusted infrastructure, require an individual to trust unknown entities, or provide relatively low probabilistic guarantees of authenticity (95% for realistic settings). This work presents SPATE, a primitive that allows users to establish trust via device mobility and physical interaction. Once the SPATE protocol runs to completion, its participants' mobile devices have authentic data that their applications can use to interact securely (i.e., the probability of a successful attack is 2-24). For this work, we leverage SPATE as part of a larger system to facilitate efficient, secure, and user-friendly collaboration via email and file-sharing services. Our implementation of SPATE on Nokia N70 smartphones allows users to establish trust in small groups of up to eight users in less than one minute. The two example SPATE applications provide increased security with no overhead noticeable to users once keys are established.

Vehicular ad hoc networks (VANETs) require a mechanism to help authenticate messages, identify valid vehicles, and remove malevolent vehicles. A public key infrastructure (PKI) can provide this functionality using certificates and fixed public keys. However, fixed keys allow an eavesdropper to associate a key with a vehicle and a location, violating drivers' privacy. In this work we propose a VANET key management scheme based on temporary anonymous certified keys (TACKs). Our scheme efficiently prevents eavesdroppers from linking a vehicle's different keys and provides timely revocation of misbehaving participants while maintaining the same or less overhead for vehicle-to-vehicle communication as the current IEEE 1609.2 standard for VANET security.

A large number of papers have proposed cryptographic protocols for establishing secure group communication. These protocols allow a set of group members to exchange or establish keys to encrypt and authenticate messages within the group. At the same time, individuals outside of the group cannot eavesdrop on group communication or inject messages. There have even been usability studies, demonstrating an average user can successfully complete some of these protocols. However, group protocols are rarely used in the real world. In this work, we conduct a survey to help uncover why the general population ignores such mechanisms for group communication. We also try to determine what protocols would best match respondents' current expectations for group protocols and methods for establishing trust. Survey results indicate that a group protocol that leverages location-limited channels, PKI, or Web-of-Trust authenticated public keys and allows addition and deletion of members fulfills the majority of users' expectations.

Establishing secure communication among a group of physically collocated people is a challenge. This problem can be reduced to establishing authentic public keys among all the participants - these public keys then serve to establish a shared secret symmetric key for encryption and authentication of messages. Unfortunately, in most real-world settings, public key infrastructures (PKI) are uncommon and distributing a secret in a public space is difficult. Thus, it is a challenge to exchange authentic public keys in a scalable, secure, and easy to use fashion.

Deploying large-scale wireless citywide networks with strong authentication mechanisms has received considerable interest in industry and academic circles. In this paper, we present modified Transport Layer Security (TLS) protocols which leverage Trusted Platform Module (TPM) technologies to achieve both user and device authentication. The first protocol leverages TPM attestation capabilities, while the other uses TPM sealed storage to achieve our goals. The proposed user and device authentication schemes can provide mutual proof between supplicants and servers not only on Wi-Fi and WiMAX interworked wireless cities, but also on any heterogeneous wireless networks which is based on the Extensible Authentication Protocol.

Group communication is inherently a social activity. However, existing protocols for group key establishment often fail to consider important social dynamics. This paper examines the human requirements for wireless group key establishment. We identify seven social and situational factors which impact group formation. Using these factors, we examine the requirements of four common classes of group communications. Each scenario imposes a unique set of requirements on wireless group key establishment.

Improving cache performance requires understanding cache behavior. However, measuring cache performance for one or two data input sets provides little insight into how cache behavior varies across all data input sets and all cache configurations. This paper uses locality analysis to generate a parameterized model of program cache behavior. Given a cache size and associativity, this model predicts the miss rate for arbitrary data input set sizes. This model also identifies critical data input sizes where cache behavior exhibits marked changes. Experiments show this technique is within 2 percent of the hit rate for set associative caches on a set of floating-point and integer programs using array and pointer-based data structures. Building on the new model, this paper presents an interactive visualization tool that uses a three-dimensional plot to show miss rate changes across program data sizes and cache sizes and its use in evaluating compiler transformations. Other uses of this visualization tool include assisting machine and benchmark-set design. The tool can be accessed on the Web at http://www.cs.rochester.edu/research/locality