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  1. We present the first formal-methods analysis of the Session Binding Proxy (SBP) protocol, which protects a vulnerable system by wrapping it and introducing a reverse proxy between the system and its clients. SBP mitigates thefts of authentication cookies by cryptographically binding the authentication cookie---issued by the server to the client---to an underlying Transport Layer Security (TLS) channel using the channel's master secret and a secret key known only by the proxy. An adversary who steals a bound cookie cannot reuse this cookie to create malicious requests on a separate connection because the cookie's channel binding will not match the adversary's channel. SBP seeks to achieve this goal without modifications to the client or the server software, rendering the client and server ``oblivious protocol participants'' that are not aware of the SBP session. Our analysis verifies that the original SBP design mitigates cookie stealing under the client's cryptographic assumptions but fails to authenticate the client to the proxy. Resulting from two issues, the proxy has no assurance that it shares a session context with a legitimate client: SBP assumes an older flawed version of TLS (1.2), and SBP relies on legacy server usernames and passwords to authenticate clients. Due to these issues, there is no guarantee of cookie-stealing resistance from the proxy's cryptographic perspective. Using the Cryptographic Protocol Shapes Analyzer (CPSA), we model and analyze the original SBP and three variations in the Dolev-Yao network intruder model. Our models differ in the version of TLS they use: 1.2 (original SBP), 1.2 with mutual authentication, 1.3, and {\it 1.3 with mutual authentication (mTLS-1.3)}. For comparison, we also analyze a model of the baseline scenario without SBP. We separately analyze each of our SBP models from two perspectives: client and proxy. In each SBP model, the client has assurance that the cookie is valid only for the client's legitimate session. Only in mTLS-1.3 does the proxy have assurance that it communicates with a legitimate client and that the client's cookie is valid. We formalize these results by stating and proving, or disproving, security goals for each model. SBP is useful because it provides a practical solution to the important challenge of protecting flawed legacy systems that cannot be patched. Our analysis of this obscure protocol sheds insight into the properties necessary for wrapper protocols to resist a Dolev-Yao adversary. When engineering wrapper protocols, designers must carefully consider authentication, freshness, and requirements of cryptographic bindings such as channel bindings. Our work exposes strengths and limitations of wrapper protocols and TLS channel bindings. 
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    Free, publicly-accessible full text available January 8, 2025
  2. We solve a long-standing challenge to the integrity of votes cast without the supervision of a voting booth: ``improper influence,'' which we define as any combination of vote buying and voter coercion. In comparison with previous proposals, our system is the first in the literature to protect against a strong adversary who learns all of the voter's keys---we call this property ``extreme coercion resistance.'' Our approach allows each voter, or their trusted agents (which we call ``hedgehogs''), to ``nullify'' (effectively cancel) their vote in a way that is unstoppable and irrevocable, and such that the nullification action is forever unattributable to that voter or their hedgehog(s). We demonstrate the security of VoteXX in the {universal composability} model. Additionally we provide concrete implementations of sub-protocols---including inalienable authentication, decentralized bulletin boards, and anonymous communication channels---that are usually left as abstract assumptions in the literature. As in many other coercion-resistant systems, voters are authorized to vote with public-private keys. Each voter registers their public keys with the Election Authority (EA) in a way that convinces the EA that the voter has complete knowledge of their private keys. Voters concerned about losing their private keys can themselves, or by delegating to one or more hedgehog(s), monitor the bulletin board for malicious ballots cast with their keys, and can act to nullify these ballots in a privacy-preserving manner with zero-knowledge proofs. In comparison with previous proposals, our system makes fewer assumptions and protects against a stronger adversary. For example, votexx makes none of the following assumptions made by previous systems: the voter must complete registration before being coerced; the election will not close before the voter can cast a ballot after coercion; the voter needs to generate a fake password to evade coercion; and the voter knows an honest Election Authority official. 
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    Free, publicly-accessible full text available September 1, 2024
  3. s a case study in cryptographic binding, we present a formal-methods analysis of the Fast IDentity Online (FIDO) Universal Authentication Framework (UAF) authentication protocol's cryptographic channel binding mechanisms. First, we show that UAF's channel bindings fail to mitigate protocol interaction by a Dolev-Yao (DY) adversary, enabling the adversary to transfer the server's authentication challenge to alternate sessions of the protocol. As a result, in some contexts, the adversary can masquerade as a client and establish an authenticated session with a server, which might be a bank server. Second, we implement a proof-of-concept man-in-the-middle attack against eBay's open source FIDO UAF implementation. Third, we propose and verify an improvement of UAF channel binding that better resists protocol interaction, in which the client and the server, rather than the client alone, bind the server's challenge to the session. The weakness we analyze is similar to the vulnerability discovered in the Needham-Schroeder protocol over 25 years ago. That this vulnerability appears in FIDO UAF highlights the strong need for protocol designers to bind messages properly and to analyze their designs with formal-methods tools. UAF's channel bindings fail for four reasons: channel binding is optional; the client cannot authenticate the server's challenge, even when channel binding is used; the standard permits the server to accept incorrect channel bindings; and the protocol binds only to the communication endpoints and not to the protocol session. We carry out our analysis of the standard and our suggested improvement using the Cryptographic Protocol Shapes Analyzer (CPSA). To our knowledge, we are first to carry out a formal-methods analysis of channel binding in FIDO UAF, first to identify the structural weakness resulting from improper binding, and first to exhibit details of an attack resulting from this weakness. In FIDO UAF, the client can cryptographically bind protocol data (including a server-generated authentication challenge) to the underlying authenticated communication channel. To facilitate the protocol's adoption, the FIDO Alliance makes the channel binding optional and allows a server to accept incorrect channel bindings, such as when the client communicates through a network perimeter proxy. Practitioners should be aware that, when omitting channel binding or accepting incorrect channel bindings, FIDO UAF is vulnerable to a protocol-interaction attack in which the adversary tricks the client and authenticator to act as confused deputies to sign an authentication challenge for the adversary. In addition to enabling the server to verify the client's binding of the challenge to the channel, our improved mandatory dual channel-binding mechanism provides the following two advantages: (1) By binding the challenge to the channel, the server provides an opportunity for the client to verify this binding. By contrast, in the current standard, the client cannot authenticate the server's challenge. (2) It performs binding at the server where the authentication challenge is created, hindering an adversary from transplanting the challenge into another protocol execution. Our case study illustrates the importance of cryptographically binding context to protocol messages to prevent an adversary from misusing messages out of context. 
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    Free, publicly-accessible full text available July 19, 2024
  4. We present a psychometric evaluation of the Cybersecurity Curriculum Assessment (CCA), completed by 193 students from seven colleges and universities. The CCA builds on our prior work developing and validating a Cybersecurity Concept Inventory (CCI), which measures students' conceptual understanding of cybersecurity after a first course in the area. The CCA deepens the conceptual complexity and technical depth expectations, assessing conceptual knowledge of students who had completed multiple courses in cybersecurity. We review our development of the CCA and present our evaluation of the instrument using Classical Test Theory and Item-Response Theory. The CCA is a difficult assessment, providing reliable measurements of student knowledge and deeper information about high-performing students. 
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  5. We solve a long-standing challenge to the integrity of votes cast without the supervision of a voting booth: ``{\it improper influence},'' which typically refers to any combination of vote buying and voter coercion. Our approach allows each voter, or their trusted agents (which we call ``{\it hedgehogs}''), to {\it ``nullify''} (effectively cancel) their vote in a way that is unstoppable, irrevocable, and forever unattributable to the voter. In particular, our approach enhances security of online, remote, public-sector elections, for which there is a growing need and the threat of improper influence is most acute. We introduce the new approach, give detailed cryptographic protocols, show how it can be applied to several voting settings, and describe our implementation. The protocols compose a full voting system, which we call {\it {\votexx}}, including registration, voting, nullification, and tallying---using an anonymous communication system for registration, vote casting, and other communication in the system. We demonstrate how the technique can be applied to known systems, including where ballots can be mailed to voters and voters use codes on the ballot to cast their votes online. In comparison with previous proposals, our system makes fewer assumptions and protects against a strong adversary who learns all of the voter's keys. In {\votexx}, each voter has two public-private key pairs. Without revealing their private keys, each voter registers their public keys with the election authority. Each voter may share their keys with one or more hedgehogs. During nullification, the voter, or one or more of their hedgehogs, can interact through the anonymous communication system to nullify a vote by proving knowledge of one of the voter's private keys via a zero-knowledge proof without revealing the private key. We describe a fully decentralizable implementation of {\votexx}, including its public bulletin board, which could be implemented on a blockchain. 
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  6. CYBERSECURITY AND LOCAL GOVERNMENT Learn to secure your local government’s networks with this one-of-a-kind resource In Cybersecurity and Local Government, a distinguished team of researchers delivers an insightful exploration of cybersecurity at the level of local government. The book makes a compelling argument that every local government official, elected or otherwise, must be reasonably knowledgeable about cybersecurity concepts and provide appropriate support for it within their governments. It also lays out a straightforward roadmap to achieving those objectives, from an overview of cybersecurity definitions to descriptions of the most common security challenges faced by local governments. The accomplished authors specifically address the recent surge in ransomware attacks and how they might affect local governments, along with advice as to how to avoid and respond to these threats. They also discuss the cybersecurity law, cybersecurity policies that local government should adopt, the future of cybersecurity, challenges posed by Internet of Things, and much more. Throughout, the authors provide relevant field examples, case studies of actual local governments, and examples of policies to guide readers in their own application of the concepts discussed within. Cybersecurity and Local Government also offers: A thorough introduction to cybersecurity generally, including definitions of key cybersecurity terms and a high-level overview of the subject for non-technologists. A comprehensive exploration of critical information for local elected and top appointed officials, including the typical frequencies and types of cyberattacks. Practical discussions of the current state of local government cybersecurity, with a review of relevant literature from 2000 to 2021. In-depth examinations of operational cybersecurity policies, procedures and practices, with recommended best practices. Perfect for local elected and top appointed officials and staff as well as local citizens, Cybersecurity and Local Government will also earn a place in the libraries of those studying or working in local government with an interest in cybersecurity. 
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  7. We explore shadow information technology (IT) at institutions of higher education through a two-tiered approach involving a detailed case study and comprehensive survey of IT professionals. In its many forms, shadow IT is the software or hardware present in a computer system or network that lies outside the typical review process of the responsible IT unit. We carry out a case study of an internally built legacy grants management system at the University of Maryland, Baltimore County that exemplifies the vulnerabilities, including cross-site scripting and SQL injection, typical of such unauthorized and ad-hoc software. We also conduct a survey of IT professionals at universities, colleges, and community colleges that reveals new and actionable information regarding the prevalence, usage patterns, types, benefits, and risks of shadow IT at their respective institutions. Further, we propose a security-based profile of shadow IT, involving a subset of elements from existing shadow IT taxonomies, which categorizes shadow IT from a security perspective. Based on this profile, survey respondents identified the predominant form of shadow IT at their institutions, revealing close similarities to findings from our case study. Through this work, we are the first to identify possible susceptibility factors associated with the occurrence of shadow IT related security incidents within academic institutions. Correlations of significance include the presence of certain graduate schools, the level of decentralization of the IT department, the types of shadow IT present, the percentage of security violations related to shadow IT, and the institution's overall attitude toward shadow IT. The combined elements of our case study, profile, and survey provide the first multifaceted view of shadow IT security at academic institutions, highlighting tension between its risks and benefits, and suggesting strategies for managing it successfully. 
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  8. We present and analyze UDM, a new protocol for user discovery in anonymous communication systems that minimizes the information disclosed to the system and users. Unlike existing systems, including those based on private set intersection, UDM learns nothing about the contact lists and social graphs of the users, is not vulnerable to off-line dictionary attacks that expose contact lists, does not reveal platform identifiers to users without the owner’s explicit permission, and enjoys low computation and communication complexity. UDM solves the following user-discovery problem. User Alice wishes to communicate with Bob over an anonymous communication system, such as cMix or Tor. Initially, each party knows each other’s public contact identifier (e.g., email address or phone number), but neither knows the other’s private platform identifier in the communication system. If both parties wish to communicate with each other, UDM enables them to establish a shared key and learn each other’s private platform identifier. UDM uses an untrusted user-discovery system, which processes and stores only public information, hashed values, or values encrypted with keys it does not know. Therefore, UDM cannot learn any information about the social graphs of its users. Using the anonymous communication system, each pair of users who wish to communicate with each other uploads to the user-discovery system their private platform identifier, encrypted with their shared key. Indexing their request by a truncated cryptographic hash of their shared key, each user can then download each other’s encrypted private platform identifier. 
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  9. null (Ed.)
    We introduce AOT, an anonymous communication system based on mix network architecture that uses oblivious transfer (OT) to deliver messages. Using OT to deliver messages helps AOT resist blending (n-1) attacks and helps AOT preserve receiver anonymity, even if a covert adversary controls all nodes in AOT. AOT comprises three levels of nodes, where nodes at each level perform a different function and can scale horizontally. The sender encrypts their payload and a tag---derived from a secret shared between the sender and receiver---with the public key of a Level-2 node and sends them to a Level-1 node. On a public bulletin board, Level-3 nodes publish tags associated with messages ready to be retrieved. Each receiver checks the bulletin board, identifies tags, and receives the associated messages using OT. A receiver can receive their messages even if the receiver is offline when messages are ready. Through what we call a ``handshake'' process, communicants can use the AOT protocol to establish shared secrets anonymously. Users play an active role in contributing to the unlinkability of messages: periodically, users initiate requests to AOT to receive dummy messages, such that an adversary cannot distinguish real and dummy requests. 
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