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1. Protecting Cryptography Against Compelled Self-Incrimination

   Scheffler, Sarah; Varia, Mayank (August 2021, Usenix Security 2021)

   null (Ed.)

   The information security community has devoted substantial effort to the design, development, and universal deployment of strong encryption schemes that withstand search and seizure by computationally-powerful nation-state adversaries. In response, governments are increasingly turning to a different tactic: issuing subpoenas that compel people to decrypt devices themselves, under the penalty of contempt of court if they do not comply. Compelled decryption subpoenas sidestep questions around government search powers that have dominated the Crypto Wars and instead touch upon a different (and still unsettled) area of the law: how encryption relates to a person's right to silence and against self-incrimination. In this work, we provide a rigorous, composable definition of a critical piece of the law that determines whether cryptosystems are vulnerable to government compelled disclosure in the United States. We justify our definition by showing that it is consistent with prior court cases. We prove that decryption is often not compellable by the government under our definition. Conversely, we show that many techniques that bolster security overall can leave one more vulnerable to compelled disclosure. As a result, we initiate the study of protecting cryptographic protocols against the threat of future compelled disclosure. We find that secure multi-party computation is particularly vulnerable to this threat, and we design and implement new schemes that are provably resilient in the face of government compelled disclosure. We believe this work should influence the design of future cryptographic primitives and contribute toward the legal debates over the constitutionality of compelled decryption. 

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2. Password-Protected Threshold Signatures

   https://doi.org/10.1007/978-981-96-0891-1_6  

   Dziembowski, Stefan; Jarecki, Stanislaw; Kedzior, Pawel; Krawczyk, Hugo; Ngo, Chan Nam; Xu, Jiayu (December 2024, Springer Nature Singapore)

   Chung, KM; Sasaki, Y (Ed.)

   We witness an increase in applications like cryptocurrency wallets, which involve users issuing signatures using private keys. To protect these keys from loss or compromise, users commonly outsource them to a custodial server. This creates a new point of failure, because compromise of such a server leaks the user’s key, and if user authentication is implemented with a password then this password becomes open to an offline dictionary attack (ODA). A better solution is to secret-share the key among a set of servers, possibly including user’s own device(s), and implement password authentication and signature computation using threshold cryptography. We propose a notion of augmented password-protected threshold signature (aptSIG) scheme which captures the best possible security level for this setting. Using standard threshold cryptography techniques, i.e. threshold password authentication and threshold signatures, one can guarantee that compromising up to t out of n servers reveals no information on either the key or the password. However, we extend this with a novel property, that compromising even all n servers also does not leak any information, except via an unavoidable ODA attack, which reveals the key only if the attacker guesses the password. We define aptSIG in the Universally Composable (UC) framework and show that it can be constructed very efficiently, using a black-box composition of any UC threshold signature [13] and a UC augmented Password-Protected Secret Sharing (aPPSS), which we define as an extension of prior notion of PPSS [30]. As concrete instantiations we obtain secure aptSIG schemes for ECDSA (in the case of t=n-1) and BLS signatures with very small overhead over the respective threshold signature. Finally, we note that both the notion and our generic solution for augmented password-protected threshold signatures can be generalized to password-protecting MPC for any keyed functions. 

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3. SPRC19: A Database of State Policy Responses to COVID-19 in the United States

   https://doi.org/10.1038/s41597-023-02343-4  

   Boehmke, Frederick J.; Desmarais, Bruce A.; Eastman, Abbie; Grassel, Isabelle; Harden, Jeffrey J.; Harper, Samuel; Kaboli, Liam; Ko, Hyein; Oster, Elisabeth; Saunders, Tracee M. (August 2023, Scientific Data)

   Abstract SPRC19 is a new database that seeks to capture a wide range of state policy actions in response to COVID-19 in the United States. Since March 2020 we have monitored state governments’ and multi-state associations’ websites for executive orders, agency rules, new legislation, and court decisions. We categorize each policy action into one of 206 distinct policies, then document the branch of government, source document, announcement date, implementation date, and expiration date (if applicable). We also record whether the action represents the introduction of a new policy or the expansion or contraction of an existing policy. The current release of SPRC19, v3.0, captures over 13,000 distinct policy actions through April 2020, which constitutes thousands more actions than similar resources over the same time period. 

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4. VICEROY: GDPR-/CCPA-compliant Enforcement of Verifiable Accountless Consumer Requests

   https://doi.org/10.14722/ndss.2023.23074  

   Jordan, Scott; Nakatsuka, Yoshimichi; Ozturk, Ercan; Paverd, Andrew; Tsudik, Gene (January 2023, The Network and Distributed System Security Symposium (NDSS))

   Recent data protection regulations (notably, GDPR and CCPA) grant consumers various rights, including the right to access, modify or delete any personal information collected about them (and retained) by a service provider. To exercise these rights, one must submit a verifiable consumer request proving that the collected data indeed pertains to them. This action is straightforward for consumers with active accounts with a service provider at the time of data collection, since they can use standard (e.g., password-based) means of authentication to validate their requests. However, a major conundrum arises from the need to support consumers without accounts to exercise their rights. To this end, some service providers began requiring such accountless consumers to reveal and prove their identities (e.g., using government-issued documents, utility bills, or credit card numbers) as part of issuing a verifiable consumer request. While understandable as a short-term fix, this approach is cumbersome and expensive for service providers as well as privacy-invasive for consumers. Consequently, there is a strong need to provide better means of authenticating requests from accountless consumers. To achieve this, we propose VICEROY, a privacy-preserving and scalable framework for producing proofs of data ownership, which form a basis for verifiable consumer requests. Building upon existing web techniques and features, VICEROY allows accountless consumers to interact with service providers, and later prove that they are the same person in a privacy-preserving manner, while requiring minimal changes for both parties. We design and implement VICEROY with emphasis on security/privacy, deployability and usability. We also assess its practicality via extensive experiments. 

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5. Conditional Encryption with Applications to Secure Personalized Password Typo Correction

   https://doi.org/10.1145/3658644.3690374  

   Ameri, Mohammad Hassan; Blocki, Jeremiah (December 2024, ACM)

   We introduce the notion of a conditional encryption scheme as an extension of public key encryption. In addition to the standard public key algorithms (KG, Enc, Dec) for key generation, encryption and decryption, a conditional encryption scheme for a binary predicate P adds a new conditional encryption algorithm CEnc. The conditional encryption algorithm c=CEncpk (c1,m2,m3) takes as input the public encryption key pk, a ciphertext c1 = Encpk (m1) for an unknown message m1, a control message m2 and a payload message m3 and outputs a conditional ciphertext c. Intuitively, if P(m1,m2)=1 then the conditional ciphertext c should decrypt to the payload message m3. On the other hand if P(m1,m2) = 0 then the ciphertext should not leak any information about the control message m2 or the payload message m3 even if the attacker already has the secret decryption key sk. We formalize the notion of conditional encryption secrecy and provide concretely efficient constructions for a set of predicates relevant to password typo correction. Our practical constructions utilize the Paillier partially homomorphic encryption scheme as well as Shamir Secret Sharing. We prove that our constructions are secure and demonstrate how to use conditional encryption to improve the security of personalized password typo correction systems such as TypTop. We implement a C++ library for our practically efficient conditional encryption schemes and evaluate the performance empirically. We also update the implementation of TypTop to utilize conditional encryption for enhanced security guarantees and evaluate the performance of the updated implementation. 

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