Standardized Vehicular Communication (VC), mainly Cooperative Awareness Messages (CAMs) and Decentralized Environmental Notification Messages (DENMs), is paramount to vehicle safety, carrying vehicle status information and reports of traffic/road-related events respectively. Broadcasted CAMs and DENMs are pseudonymously authenticated for security and privacy protection, with each node needing to have all incoming messages validated within an expiration deadline. This creates an asymmetry that can be easily exploited by external adversaries to launch a clogging Denial of Service (DoS) attack: each forged VC message forces all neighboring nodes to cryptographically validate it; at increasing rates, easy to generate forged messages gradually exhaust processing resources and severely degrade or deny timely validation of benign CAMs/DENMs. The result can be catastrophic when awareness of neighbor vehicle positions or critical reports are missed. We address this problem making the standardized VC pseudonymous authentication DoS-resilient. We propose efficient cryptographic constructs, which we term message verification facilitators, to prioritize processing resources for verification of potentially valid messages among bogus messages and verify multiple messages based on one signature verification. Any message acceptance is strictly based on public-key based message authentication/verification for accountability, i.e., non-repudiation is not sacrificed, unlike symmetric key based approaches. This further enables drastic misbehavior detection, also exploiting the newly introduced facilitators, based on probabilistic signature verification and cross-checking over multiple facilitators verifying the same message; while maintaining verification latency low even when under attack, trading off modest communication overhead. Our facilitators can also be used for efficient discovery and verification of DENM or any event-driven message, including misbehavior evidence used for our scheme. Even when vehicles are saturated by adversaries mounting a clogging DoS attack, transmitting high-rate bogus CAMs/DENMs, our scheme achieves an average 50 ms verification delay with message expiration ratio less than 1%- a huge improvement over the current standard that verifies every message signature in a First-Come First-Served (FCFS) manner and suffers from having 50% to nearly 100% of the received benign messages expiring.

In Vehicular Communication (VC) systems, neighboring vehicles exchange authenticated transportation safety messages, informing about own mobility and the environment. Verifying all received messages in a dense neighborhood introduces significant cryptographic computation overhead for resource-constrained vehicular On-Board Units (OBUs). Attackers can exploit this to launch Denial of Service (DoS) attacks to clog OBUs by broadcasting bogus messages at a high rate. This attack is particularly effective due to an inherent asymmetry and amplification factor: each safety message is to be validated by all receiving neighboring vehicles. This imbalance can lead to significant delays in sifting benign messages amidst a deluge of bogus messages. Even worse, failure to promptly verify a significant amount of benign messages can paralyze Vehicle-to-Vehicle (V2V) enabled applications. We address this challenge, proposing a mechanism that thwarts such attacks: puzzle-based pre-validation that prioritizes verification of potentially valid messages with yet unknown (i.e., unverified) Pseudonymous Certificates (PCs). Verification of such PCs (and their corresponding messages) can bootstrap the efficient pre-validation of follow-up messages authenticated by the same PCs. We show experimental results confirming our scheme can effectively mitigate unsophisticated clogging DoS attacks that do not attempt to solve puzzles. We further show our scheme also significantly raises the bar for sophisticated adversaries: it can be configured to force attackers to solve puzzles for their bogus messages actively - something possible only by investing in significantly higher (hundreds of times more) computational power than that of the targeted benign vehicles. Last but not least, our scheme can be adaptive while remaining compatible to standardized V2V security.

The Domain Name System (DNS) is central to all Internet user activity, resolving accessed domain names into Internet Protocol (IP) addresses. As a result, curious DNS resolvers can learn everything about Internet users' interests. Public DNS resolvers are rising in popularity, offering low-latency resolution, high reliability, privacy-preserving policies, and support for encrypted DNS queries. However, client-resolver traffic encryption, increasingly deployed to protect users from eavesdroppers, does not protect users against curious resolvers. Similarly, privacy-preserving policies are based solely on written commitments and do not provide technical safeguards. Although DNS query relay schemes can separate duties to limit data accessible by each entity, they cannot prevent colluding entities from sharing user traffic logs. Thus, a key challenge remains: organizations operating public DNS resolvers, accounting for the majority of DNS resolutions, can potentially collect and analyze massive volumes of Internet user activity data. With DNS infrastructure that cannot be fully trusted, can we safeguard user privacy? We answer positively and advocate for a user-driven approach to reduce exposure to DNS services. We will discuss key ideas of the proposal, which aims to achieve a high level of privacy without sacrificing performance: maintaining low latency, network bandwidth, memory/storage overhead, and computational overhead.

The Domain Name System (DNS) is involved in practically all web activity, translating easy-to-remember domain names into Internet Protocol (IP) addresses. Due to its central role on the Internet, DNS exposes user web activity in detail. The privacy challenge is honest-but-curious DNS servers/resolvers providing the translation/lookup service. In particular, with the majority of DNS queries handled by public DNS resolvers, the organizations running them can track, collect, and analyze massive user activity data. Existing solutions that encrypt DNS traffic between clients and resolvers are insufficient, as the resolver itself is the privacy threat. While DNS query relays separate duties among multiple entities, to limit the data accessible by each entity, they cannot prevent colluding entities from sharing user traffic logs. To achieve near-zero-trust DNS privacy compatible with the existing DNS infrastructure, we propose LLUAD: it locally stores a Popularity List, the most popular DNS records, on user devices, formed in a privacy-preserving manner based on user interests. In this way, LLUAD can both improve privacy and reduce access times to web content. The Popularity List is proactively retrieved from a (curious) public server that continually updates and refreshes the records based on user popularity votes, while efficiently broadcasting record updates/changes to adhere to aggressive load-balancing schemes (i.e., name servers actively load-balancing user connections by changing record IP addresses). User votes are anonymized using a novel, efficient, and highly scalable client-driven Voting Mix Network – with packet lengths independent of the number of hops, centrally enforced limit on number of votes cast per user, and robustness against poor client participation – to ensure a geographically relevant and correctly/securely instantiated Popularity List. We find that with a 25 000 entries long Popularity List, LLUAD provides both privacy-preserving and high performance DNS: this is due to the instant local (and anonymous) resolution of around 94% of queries based on the Popularity List, with the few remaining queries using other privacy-preserving, but latency-costly, alternatives, such as querying a public resolver over a public anonymous network, e.g., Tor. Beyond strong DNS privacy and low average lookup latency, LLUAD maintains network traffic overhead on par with widely deployed secure DNS protocols, with a memory/storage overhead of less than 2 MB.

The Domain Name System (DNS) is involved in practically all web activity, translating easy-to-remember domain names into Internet Protocol (IP) addresses. Due to its central role on the Internet, DNS exposes user web activity in detail. The privacy challenge is honest-but-curious DNS servers/resolvers providing the translation/lookup service. In particular, with the majority of DNS queries handled by public DNS resolvers, the organizations running them can track, collect, and analyze massive user activity data. Existing solutions that encrypt DNS traffic between clients and resolvers are insufficient, as the resolver itself is the privacy threat. While DNS query relays separate duties among multiple entities, to limit the data accessible by each entity, they cannot prevent colluding entities from sharing user traffic logs. To achieve near-zero-trust DNS privacy compatible with the existing DNS infrastructure, we propose LLUAD: it locally stores a Popularity List, the most popular DNS records, on user devices, formed in a privacy-preserving manner based on user interests. In this way, LLUAD can both improve privacy and reduce access times to web content. The Popularity List is proactively retrieved from a (curious) public server that continually updates and refreshes the records based on user popularity votes, while efficiently broadcasting record updates/changes to adhere to aggressive load-balancing schemes (i.e., name servers actively load-balancing user connections by changing record IP addresses). User votes are anonymized using a novel, efficient, and highly scalable client-driven Voting Mix Network - with packet lengths independent of the number of hops, centrally enforced limit on number of votes cast per user, and robustness against poor client participation - to ensure a geographically relevant and correctly/securely instantiated Popularity List. We find that with a 25 000 entries long Popularity List, LLUAD provides both privacy-preserving and high performance DNS: this is due to the instant local (and anonymous) resolution of around 94 % of queries based on the Popularity List, with the few remaining queries using other privacy-preserving, but latency-costly, alternatives, such as querying a public resolver over a public anonymous network, e.g., Tor. Beyond strong DNS privacy and low average lookup latency, LLUAD maintains network traffic overhead on par with widely deployed secure DNS protocols, with a memory/storage overhead of less than 2MB.

Vehicular Communication Systems (VCSs) enhance safety by enabling communication among vehicles and road-side infrastructure. To provide secure communication and privacy, a Vehicular Public-Key Infrastructure (VPKI) distributes long-term and temporary credentials (pseudonyms) to validate Cooperative Awareness Messages (CAMs) and other communication by registered vehicles. However, improperly designed pseudonym-based privacy techniques are still vulnerable to pseudonym linking based on their issuer, i.e., a specific Pseudonymous Certification Authority (PCA) that signed the pseudonyms in one batch, in the presence of PCAs. As each PCA digitally signs pseudonyms, the presence of distinct PCAs makes linking pseudonyms easier. We propose two strategies, Interleaved Pseudonym Distribution (IPD) and Random Interleaved Pseudonym Distribution (RIPD), to mitigate linking. Multi-PCA collaboration allows distributing interleaved pseudonyms (issued by different PCAs), reducing linkability. To assess our scheme privacy enhancement, a PCA_id-based pseudonym linking algorithm is developed utilizing a Kalman filter and road information to track vehicles. Simulation results show that IPD provides a moderate improvement in pseudonym confusion, while RIPD significantly disrupts PCA_id-based linking, enhancing vehicle privacy. The proof-of-concept implementation of our scheme shows the efficiency of our scheme, compared to the baseline that a single PCA issues all pseudonyms within one request.

Clogging Denial of Service (DoS) attacks have disrupted or disabled various networks, in spite of security mechanisms. External adversaries can severely harm networks, especially when high-overhead security mechanisms are deployed in resource-constrained systems. This can be especially true in the emerging standardized secure Vehicular Communication (VC) systems: mandatory message signature verification can be exploited to exhaust resources and prevent validating incoming messages sent by neighboring vehicles, information that is critical, often, for transportation safety. Efficient message verification schemes and better provisioned devices could serve as potential remedies, but existing solutions have limitations. We point out those and identify, challenges to address for scalable and resilient secure Vehicular Communication (VC) systems, and, most notably, the need for integrating defense mechanisms against clogging Denial of Service (DoS) attacks. We take the position that existing secure Vehicular Communication (VC) protocols are vulnerable to clogging Denial of Service (DoS) attacks and recommend symmetric key chain based pre-validation with mandatory signature verification to thwart clogging Denial of Service (DoS) attacks, while maintaining all key security properties, including non-repudiation to enable accountability.

Medium Access Control (MAC) address randomization is a key component for privacy protection in Wi-Fi networks. Current proposals periodically change the mobile device MAC addresses when it disconnects from the Access Point (AP). This way frames cannot be linked across changes, but the mobile device presence is exposed as long as it remains connected: all its communication is trivially linkable by observing the randomized yet same MAC address throughout the connection. Our runtime MAC re-randomization scheme addresses this issue, reducing or eliminating Wi-Fi frames linkability without awaiting for or requiring a disconnection. Our MAC re-randomization is practically 'over-the-air': MAC addresses are re-randomized just before transmission, while the protocol stacks (at the mobile and the AP) maintain locally the original connection MAC addresses - making our MAC layer scheme transparent to upper layers. With an implementation and a set of small-scale experiments with off-the-shelf devices, we show the feasibility of our scheme and the potential towards future deployment.

Recently released Wi-Fi adapters, such as Intel AX200 802.11ax NIC, support both Channel State Information (CSI) measurement and Fine Time Measurement (FTM). Angle of Arrival (AoA) estimation with CSI, using MUltiple SIgnal Classification (MUSIC), and FTM are both promising localization methods. But each suffers from practical constraints pertinent to the specific hardware and firmware used. The result can be rather inaccurate localization if AoA or FTM alone were used. We identify the issues/challenges specific to AX200, and as a remedy, we propose a localization approach that combines both CSI-based AoA and FTM. Our approach does not require any modification of the localization target device. This makes the solution readily available for localizing smartphones or any WiFi devices with FTM functionality. Our experimental evaluation shows that our approach achieves a successful localization ratio of 80%, with localization error less than 1 m; and less than 0.5 m for 66% of the experiments.

Authenticated safety beacons in Vehicular Communication (VC) systems ensure awareness among neighboring vehicles. However, the verification of beacon signatures introduces significant processing overhead for resource-constrained vehicular On-Board Units (OBUs). Even worse in dense neighborhood or when a clogging Denial of Service (DoS) attack is mounted. The OBU would fail to verify for all received (authentic or fictitious) beacons. This could significantly delay the verifications of authentic beacons or even affect the awareness of neighboring vehicle status. In this paper, we propose an efficient cooperative beacon verification scheme leveraging efficient symmetric key based authentication on top of pseudonymous authentication (based on traditional public key cryptography), providing efficient discovery of authentic beacons among a pool of received authentic and fictitious beacons, and can significantly decrease waiting times of beacons in queue before their validations. We show with simulation results that our scheme can guarantee low waiting times for received beacons even in high neighbor density situations and under DoS attacks, under which a traditional scheme would not be workable. rights reserved.