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01 December 2023
Tomoyuki Morimae, Barak Nehoran, Takashi Yamakawa
We show the following unconditional results on quantum commitments in two related yet different models:
1. We revisit the notion of quantum auxiliary-input commitments introduced by Chailloux, Kerenidis, and Rosgen (Comput. Complex. 2016) where both the committer and receiver take the same quantum state, which is determined by the security parameter, as quantum auxiliary inputs. We show that computationally-hiding and statistically-binding quantum auxiliary-input commitments exist unconditionally, i.e., without relying on any unproven assumption, while Chailloux et al. assumed a complexity-theoretic assumption, ${\bf QIP}\not\subseteq{\bf QMA}$. On the other hand, we observe that achieving both statistical hiding and statistical binding at the same time is impossible even in the quantum auxiliary-input setting. To the best of our knowledge, this is the first example of unconditionally proving computational security of any form of (classical or quantum) commitments for which statistical security is impossible. As intermediate steps toward our construction, we introduce and unconditionally construct post-quantum sparse pseudorandom distributions and quantum auxiliary-input EFI pairs which may be of independent interest.
2. We introduce a new model which we call the common reference quantum state (CRQS) model where both the committer and receiver take the same quantum state that is randomly sampled by an efficient setup algorithm. We unconditionally prove that there exist statistically hiding and statistically binding commitments in the CRQS model, circumventing the impossibility in the plain model.
We also discuss their applications to zero-knowledge proofs, oblivious transfers, and multi-party computations.
1. We revisit the notion of quantum auxiliary-input commitments introduced by Chailloux, Kerenidis, and Rosgen (Comput. Complex. 2016) where both the committer and receiver take the same quantum state, which is determined by the security parameter, as quantum auxiliary inputs. We show that computationally-hiding and statistically-binding quantum auxiliary-input commitments exist unconditionally, i.e., without relying on any unproven assumption, while Chailloux et al. assumed a complexity-theoretic assumption, ${\bf QIP}\not\subseteq{\bf QMA}$. On the other hand, we observe that achieving both statistical hiding and statistical binding at the same time is impossible even in the quantum auxiliary-input setting. To the best of our knowledge, this is the first example of unconditionally proving computational security of any form of (classical or quantum) commitments for which statistical security is impossible. As intermediate steps toward our construction, we introduce and unconditionally construct post-quantum sparse pseudorandom distributions and quantum auxiliary-input EFI pairs which may be of independent interest.
2. We introduce a new model which we call the common reference quantum state (CRQS) model where both the committer and receiver take the same quantum state that is randomly sampled by an efficient setup algorithm. We unconditionally prove that there exist statistically hiding and statistically binding commitments in the CRQS model, circumventing the impossibility in the plain model.
We also discuss their applications to zero-knowledge proofs, oblivious transfers, and multi-party computations.
Mike Nkongolo Wa Nkongolo
This study focuses on spotting and stopping new types of online threats by improving the UGRansome dataset to detect unusual activity in real-time. By blending different machine learning methods, like naïve tree-based ensemble learning and recursive feature elimination (RFE), the research achieves a high accuracy rate of 97%. Naïve Bayes (NB) stands out as the most effective classifier. The suggested setup, combining gradient boosting (GB) and random forest (RF) with NB, effectively identifies and prevents unknown vulnerabilities in computer systems. UGRansome successfully blocks over 100 kilobits per second (kbps) of harmful online traffic by using details pinpointed by the RFE method, specifically uniform resource locators (URLs). This outperforms existing Intrusion Detection System (IDS) datasets. It's particularly good at stopping secure shell attacks, proving the dataset's usefulness in making networks safer. This research marks significant progress in detecting intrusions. The NB model excels in accuracy, precision, and remembering patterns, especially in identifying new threats. Moreover, the suggested naïve tree-based ensemble model shows outstanding accuracy, standing out as the best-performing technique among all models studied. Applying the UGRansome properties-based rule noticeably changes how traffic is sorted, decreasing unknown traffic while increasing unclassified traffic, which requires more investigation.
Xihan Xiong, Zhipeng Wang, Xi Chen, William Knottenbelt, Michael Huth
Lido, the leading Liquidity Staking Derivative (LSD) provider on Ethereum, allows users to stake an arbitrary amount of ETH to receive stETH, which can be integrated with Decentralized Finance (DeFi) protocols such as Aave. The composability between Lido and Aave enables a novel strategy called “leverage staking”, where users stake ETH on Lido to acquire stETH, utilize stETH as collateral on Aave to borrow ETH, and then restake the borrowed ETH on Lido. Users can iteratively execute this process to optimize potential returns based on their risk profile.
This paper systematically studies the opportunities and risks associated with leverage staking. We are the first to formalize the stETH-ETH leverage staking strategy within the Lido-Aave ecosystem. Our empirical study identifies 262 leverage staking positions on Ethereum, with an aggregated staking amount of 295,243 ETH (482M USD). We discover that 90.13% of leverage staking positions have achieved higher returns than conventional staking. Furthermore, we perform stress tests to evaluate the risk introduced by leverage staking under extreme conditions. We find that leverage staking significantly amplifies the risk of cascading liquidations. We hope this paper can inform and encourage the development of robust risk management approaches to protect the Lido-Aave LSD ecosystem.
This paper systematically studies the opportunities and risks associated with leverage staking. We are the first to formalize the stETH-ETH leverage staking strategy within the Lido-Aave ecosystem. Our empirical study identifies 262 leverage staking positions on Ethereum, with an aggregated staking amount of 295,243 ETH (482M USD). We discover that 90.13% of leverage staking positions have achieved higher returns than conventional staking. Furthermore, we perform stress tests to evaluate the risk introduced by leverage staking under extreme conditions. We find that leverage staking significantly amplifies the risk of cascading liquidations. We hope this paper can inform and encourage the development of robust risk management approaches to protect the Lido-Aave LSD ecosystem.
Alper Çakan, Vipul Goyal
Quantum no-cloning theorem gives rise to the intriguing possibility of quantum copy protection where we encode a program in a quantum state such that a user in possession of $k$ such states cannot create $k+1$ working copies. Introduced by Aaronson (CCC'09) over a decade ago, copy protection has proven to be notoriously hard to achieve.
In this work, we construct public-key encryption and functional encryption schemes whose secret keys are copy-protected against unbounded collusions in the plain model (i.e. without any idealized oracles), assuming (post-quantum) subexponentially secure $\mathcal{iO}$, one-way functions and LWE. This resolves a long-standing open question of constructing fully collusion-resistant copy-protected functionalities raised by multiple previous works.
Prior to our work, copy-protected functionalities were known only in restricted collusion models where either an a-priori bound on the collusion size was needed, in the plain model with the same assumptions as ours (Liu, Liu, Qian, Zhandry [TCC'22]), or adversary was only prevented from doubling their number of working programs, in a structured quantum oracle model (Aaronson [CCC'09]).
We obtain our results through a novel technique which uses identity-based encryption to construct unbounded collusion resistant copy-protection schemes from $1\to2$ secure schemes. This is analogous to the technique of using digital signatures to construct full-fledged quantum money from single banknote schemes (Lutomirski et al. [ICS'09], Farhi et al. [ITCS'12], Aaronson and Christiano [STOC'12]). We believe our technique is of independent interest.
Along the way, we also construct a puncturable functional encryption scheme whose master secret key can be punctured at all functions $f$ such that $f(m_0) \neq f(m_1)$. This might also be of independent interest.
In this work, we construct public-key encryption and functional encryption schemes whose secret keys are copy-protected against unbounded collusions in the plain model (i.e. without any idealized oracles), assuming (post-quantum) subexponentially secure $\mathcal{iO}$, one-way functions and LWE. This resolves a long-standing open question of constructing fully collusion-resistant copy-protected functionalities raised by multiple previous works.
Prior to our work, copy-protected functionalities were known only in restricted collusion models where either an a-priori bound on the collusion size was needed, in the plain model with the same assumptions as ours (Liu, Liu, Qian, Zhandry [TCC'22]), or adversary was only prevented from doubling their number of working programs, in a structured quantum oracle model (Aaronson [CCC'09]).
We obtain our results through a novel technique which uses identity-based encryption to construct unbounded collusion resistant copy-protection schemes from $1\to2$ secure schemes. This is analogous to the technique of using digital signatures to construct full-fledged quantum money from single banknote schemes (Lutomirski et al. [ICS'09], Farhi et al. [ITCS'12], Aaronson and Christiano [STOC'12]). We believe our technique is of independent interest.
Along the way, we also construct a puncturable functional encryption scheme whose master secret key can be punctured at all functions $f$ such that $f(m_0) \neq f(m_1)$. This might also be of independent interest.
Luowen Qian
We demonstrate how to build computationally secure commitment schemes with the aid of quantum auxiliary inputs without unproven complexity assumptions. Furthermore, the quantum auxiliary input can be prepared either (1) efficiently through a trusted setup similar to the classical common random string model, or (2) strictly between the two involved parties in uniform exponential time. Classically this remains impossible without first proving $\mathsf{P} \neq \mathsf{NP}$.
Charanjit S Jutla, Chengyu Lin
We extend the known pseudorandomness of Ring-LWE to be based on lattices that do not correspond to any ideal of any order in the underlying number field. In earlier works of Lyubashevsky et al (EUROCRYPT 2010) and Peikert et al (STOC 2017), the hardness of RLWE was based on ideal lattices of ring of integers of number fields, which are known to be Dedekind domains. While these works extended Regev's (STOC 2005) quantum polynomial-time reduction for LWE, thus allowing more efficient and more structured cryptosystems, the additional algebraic structure of ideals of Dedekind domains leaves open the possibility that such ideal lattices are not as hard as general lattices.
In this work we show that hardness of $q$-Ring-LWE can be based on worst-case hardness of ideal lattices in arbitrary orders $O$, as long as the order $O$ satisfies the property that $\frac{1}{m}\cdot O$ contains the ring of integers, for some $m$ co-prime to $q$. Further, the hard lattice problems need not be given the order $O$ itself as input. The reduction requires that the noise be a factor $m$ more than the original Ring-LWE reduction. We also show that for the power-of-two cyclotomic number fields, there exist orders with $m=4$ such that non-trivial ideals of the order, which are not contained in the conductor, are non-invertible.
Another reduction shows that hardness of $q$-Ring-LWE can be based on worst-case hardness of lattices that correspond to sum of ideal-lattices in arbitrary and different orders in the number field, as long as the (set of) orders $\{O_i\}$ satisfy the property that $\frac{1}{m}\cdot O_i$ contains the ring of integers, for some $m$ co-prime to $q$. We also show that for the power-of-two cyclotomic number fields, there exist orders $O_1, O_2$ with $m=8$ such that there are ideals $I_1, I_2$ of $O_1, O_2$ resp. with $I_1+ I_2$ not an ideal of any order in the number field.
In this work we show that hardness of $q$-Ring-LWE can be based on worst-case hardness of ideal lattices in arbitrary orders $O$, as long as the order $O$ satisfies the property that $\frac{1}{m}\cdot O$ contains the ring of integers, for some $m$ co-prime to $q$. Further, the hard lattice problems need not be given the order $O$ itself as input. The reduction requires that the noise be a factor $m$ more than the original Ring-LWE reduction. We also show that for the power-of-two cyclotomic number fields, there exist orders with $m=4$ such that non-trivial ideals of the order, which are not contained in the conductor, are non-invertible.
Another reduction shows that hardness of $q$-Ring-LWE can be based on worst-case hardness of lattices that correspond to sum of ideal-lattices in arbitrary and different orders in the number field, as long as the (set of) orders $\{O_i\}$ satisfy the property that $\frac{1}{m}\cdot O_i$ contains the ring of integers, for some $m$ co-prime to $q$. We also show that for the power-of-two cyclotomic number fields, there exist orders $O_1, O_2$ with $m=8$ such that there are ideals $I_1, I_2$ of $O_1, O_2$ resp. with $I_1+ I_2$ not an ideal of any order in the number field.
Daniel J. Bernstein
There appears to be a widespread belief that some processes of selecting cryptosystems are less risky than other processes. As a case study of quantifying the difference in risks, this paper compares the currently-known-failure rates of three large groups of cryptosystems: (1) the round-1 submissions to the NIST Post-Quantum Cryptography Standardization Project, (2) the round-1 submissions not broken by the end of round 1, and (3) the round-1 submissions selected by NIST for round 2 of the same project. These groups of cryptosystems turn out to have currently-known-failure rates that are strikingly high, and that include statistically significant differences across the groups, not matching the pattern of differences that one might expect. Readers are cautioned that the actual failure rates could be much higher than the currently-known-failure rates.
Daniel R. L. Brown, Chris Monico
Panny [3] described how to forge the “tropical signatures” proposed by Chen, Grigoriev and Shpilrain [1]. (These signatures are loosely related to the NP-complete problem of factoring tropical polynomials).
We describe more methods to forge these tropical signatures. We also describe some patches that thwart all but one of these forgery methods (which we summarize as re-hashing an honest signature).
Hamza Abusalah, Valerio Cini
A proof of sequential work (PoSW) scheme allows the prover to convince a verifier that it computed a certain number of computational steps sequentially.
Very recently, graph-labeling PoSW schemes, found applications in light-client blockchain protocols, most notably bootstrapping. A bootstrapping protocol allows a light client, with minimal information about the blockchain, to hold a commitment to its stable prefix. An incremental PoSW (iPoSW) scheme allows the prover to non-trivially increment proofs: given $\chi,\pi_1$ and integers $N_1,N_2$ such that $\pi_1$ is a valid proof for $N_1$, it generates a valid proof $\pi$ for $N_1+N_2$.
In this work, we construct an iPoSW scheme based on the skiplist-based PoSW scheme of Abusalah et al. and prove its security in the random oracle model by employing the powerful on-the-fly sampling technique of Döttling et al. Moreover, unlike the iPoSW scheme of Döttling et al., ours is the first iPoSW scheme which is suitable for constructing incremental non-interactive arguments of chain knowledge (SNACK) schemes, which are at the heart of space and time efficient blockchain light-client protocols. In particular, our scheme works for general weight distributions, which we characterize as incrementally sampleable distributions. Our general treatment recovers the distribution underlying the scheme of Döttling et al. as well as the distribution underlying SNACK-enabled bootstrapping application as special cases. In realizing our general construction, we develop a new on-the-fly sampling technique.
Apurva K Vangujar, Alia Umrani, Paolo Palmieri
Vehicle Ad Hoc Networks (VANETs) play a pivotal role in intelligent transportation systems, offering dynamic communication between vehicles, Road Side Units (RSUs), and the internet. Given the open-access nature of VANETs and the associated threats, such as impersonation and privacy violations, ensuring the security of these communications is of utmost importance.
This paper presents the Identity-based Cluster Authentication and Key Exchange (ID-CAKE) scheme, a new approach to address security challenges in VANETs. The ID-CAKE scheme integrates the Cluster Consensus Identity-based Identification (CCIBI) with Zero-Knowledge (ZK) proofs and the Identity-based Multireceiver Key Exchange Mechanism (ID-mKEM) signature scheme. This integration provides robust authorization via CCIBI, while ID-mKEM signatures ensure message integrity, and guarantee both non-repudiation and unforgeability through mKEM for message broadcasting. The scheme employs a novel three-party ZK proof for batch verification using mKEM, which significantly reduces computational burdens. Our scheme also ensures anonymity and unlinkability by introducing pseudo-identities to all users in the cluster. The rigorous security proofs provided confirm the resilience of the ID-CAKE scheme against potential attacks, adhering to the different scenarios, against the hardness of the elliptic curve computational Diffie-Hellman under the random oracle model. The ID-CAKE scheme establishes a robust security framework for VANETs, and its introduction highlights potential pathways for future exploration in the realm of VANET security.
Ritam Bhaumik, Mohammad Amin Raeisi
In spite of being a popular technique for designing block ciphers, Lai-Massey networks have received considerably less attention from a security analysis point-of-view than Feistel networks and Substitution-Permutation networks. In this paper we study the beyond-birthday-bound (BBB) security of Lai-Massey networks with independent random round functions against chosen-plaintext adversaries. Concretely, we show that five rounds are necessary and sufficient to achieve BBB security.
Hosein Hadipour, Yosuke Todo
QARMAv2 is a general-purpose and hardware-oriented family of lightweight tweakable block ciphers (TBCs) introduced in ToSC 2023. QARMAv2, as a redesign of QARMA with a longer tweak and tighter security margins, is also designed to be suitable for cryptographic memory protection and control flow integrity. The designers of QARMAv2 provided a relatively comprehensive security analysis in the design specification, e.g., some bounds for the number of attacked rounds in differential and boomerang analysis, together with some concrete impossible differential, zero-correlation, and integral distinguishers. As one of the first third-party cryptanalysis of QARMAv2, Hadipour et al. significantly improved the integral distinguishers of QARMAv2 and provided the longest concrete distinguishers of QARMAv2 up to now. However, they provided no key recovery attack based on their distinguishers.
This paper delves into the cryptanalysis of QARMAv2 to enhance our understanding of its security. Given that the integral distinguishers of QARMAv2 are the longest concrete distinguishers for this cipher so far, we focus on integral attack. To this end, we first further improve the automatic tool introduced by Hadipour et al., for finding integral distinguishers of TBCs following the TWEAKEY framework. This new tool exploits the MixColumns property of QARMAv2 to find integral distinguishers more suitable for key recovery attacks. Then, we combine several techniques for integral key recovery attacks, e.g., Meet-in-the-middle and partial-sum techniques to build a fine-grained integral key recovery attack on QARMAv2. Notably, we demonstrate how to leverage the low data complexity of the integral distinguishers of QARMAv2 to reduce the memory complexity of the meet-in-the-middle technique. As a result, we managed to propose the first concrete key recovery attacks on reduced-round versions of QARMAv2 by attacking 13 rounds of QARMAv2-64-128 with a single tweak block, 14 rounds of QARMAv2-64-128 with two independent tweak blocks, and 16 rounds of QARMAv2-128-256 with two independent tweak blocks. Our attacks do not compromise the claimed security of QARMAv2, but they shed more light on the cryptanalysis of this cipher.
This paper delves into the cryptanalysis of QARMAv2 to enhance our understanding of its security. Given that the integral distinguishers of QARMAv2 are the longest concrete distinguishers for this cipher so far, we focus on integral attack. To this end, we first further improve the automatic tool introduced by Hadipour et al., for finding integral distinguishers of TBCs following the TWEAKEY framework. This new tool exploits the MixColumns property of QARMAv2 to find integral distinguishers more suitable for key recovery attacks. Then, we combine several techniques for integral key recovery attacks, e.g., Meet-in-the-middle and partial-sum techniques to build a fine-grained integral key recovery attack on QARMAv2. Notably, we demonstrate how to leverage the low data complexity of the integral distinguishers of QARMAv2 to reduce the memory complexity of the meet-in-the-middle technique. As a result, we managed to propose the first concrete key recovery attacks on reduced-round versions of QARMAv2 by attacking 13 rounds of QARMAv2-64-128 with a single tweak block, 14 rounds of QARMAv2-64-128 with two independent tweak blocks, and 16 rounds of QARMAv2-128-256 with two independent tweak blocks. Our attacks do not compromise the claimed security of QARMAv2, but they shed more light on the cryptanalysis of this cipher.
Noam Mazor, Rafael Pass
The relationships between various meta-complexity problems are not well understood in the worst-case regime, including whether the search version is harder than the decision version, whether the hardness scales with the ``threshold", and how the hardness of different meta complexity problems relate to one another, and to the task of function inversion.
In this note, we present resolutions to some of these questions with respect to the \emph{black-box} analog of these problems. In more detail, let $MK^t_MP[s]$ denote the language consisting of strings $x$ with $K_{M}^t(x) < s(|x|)$, where $K_M^t(x)$ denotes the $t$-bounded Kolmogorov complexity of $x$ with $M$ as the underlying (Universal) Turing machine, and let $search-MK^t_MP[s]$ denote the search version of the same problem.
We show that if there for every Universal Turing machine $U$ there exists a $2^{\alpha n}poly(n)$-size $U$-oracle aided circuit deciding $MK^t_UP [n-O(1)]$, then for every function $s$, and every not necessarily universal Turing machine $M$, there exists a $2^{\alpha s(n)}poly(n)$ size $M$-oracle aided circuit solving $search-MK^t_MP[s(n)]$; this in turn yields circuits of roughly the same size for both the Minimum Circuit Size Problem (MCSP), and the function inversion problem, as they can be thought of as instantiating $MK^t_MP$ with particular choices of (a non universal) TMs $M$ (the circuit emulator for the case of MCSP, and the function evaluation in the case of function inversion).
As a corollary of independent interest, we get that the complexity of black-box function inversion is (roughly) the same as the complexity of black-box deciding $MK^t_UP[n-O(1)]$ for any universal TM $U$; that is, also in the worst-case regime, black-box function inversion is ``equivalent" to black-box deciding $MKtUP$.
In this note, we present resolutions to some of these questions with respect to the \emph{black-box} analog of these problems. In more detail, let $MK^t_MP[s]$ denote the language consisting of strings $x$ with $K_{M}^t(x) < s(|x|)$, where $K_M^t(x)$ denotes the $t$-bounded Kolmogorov complexity of $x$ with $M$ as the underlying (Universal) Turing machine, and let $search-MK^t_MP[s]$ denote the search version of the same problem.
We show that if there for every Universal Turing machine $U$ there exists a $2^{\alpha n}poly(n)$-size $U$-oracle aided circuit deciding $MK^t_UP [n-O(1)]$, then for every function $s$, and every not necessarily universal Turing machine $M$, there exists a $2^{\alpha s(n)}poly(n)$ size $M$-oracle aided circuit solving $search-MK^t_MP[s(n)]$; this in turn yields circuits of roughly the same size for both the Minimum Circuit Size Problem (MCSP), and the function inversion problem, as they can be thought of as instantiating $MK^t_MP$ with particular choices of (a non universal) TMs $M$ (the circuit emulator for the case of MCSP, and the function evaluation in the case of function inversion).
As a corollary of independent interest, we get that the complexity of black-box function inversion is (roughly) the same as the complexity of black-box deciding $MK^t_UP[n-O(1)]$ for any universal TM $U$; that is, also in the worst-case regime, black-box function inversion is ``equivalent" to black-box deciding $MKtUP$.
François Delobel, Patrick Derbez, Arthur Gontier, Loïc Rouquette, Christine Solnon
An important criteria to assert the security of a cryptographic primitive is its resistance against differential cryptanalysis. For word-oriented primitives, a common technique to determine the number of rounds required to ensure the immunity against differential distinguishers is to consider truncated differential characteristics and to count the number of active S-boxes. Doing so allows one to provide an upper bound on the probability of the best differential characteristic with a reduced computational cost. However, in order to design very efficient primitives, it might be needed to evaluate the probability more accurately. This is usually done in a second step, during which one tries to instantiate truncated differential characteristics with actual values and computes its corresponding probability. This step is usually done either with ad-hoc algorithms or with CP, SAT or MILP models that are solved by generic solvers. In this paper, we present a generic tool for automatically generating these models to handle all word-oriented ciphers. Furthermore the running times to solve these models are very competitive
with all the previous dedicated approaches.
Ertem Nusret Tas, Dan Boneh
Dynamic vector commitments that enable local updates of opening proofs have applications ranging from verifiable databases with membership changes to stateless clients on blockchains. In these applications, each user maintains a relevant subset of the committed messages and the corresponding opening proofs with the goal of ensuring a succinct global state. When the messages are updated, users are given some global update information and update their opening proofs to match the new vector commitment. We investigate the relation between the size of the update information and the runtime complexity needed to update an individual opening proof. Existing vector commitment schemes require that either the information size or the runtime scale linearly in the number $k$ of updated state elements. We construct a vector commitment scheme that asymptotically achieves both length and runtime that is sublinear in $k$, namely $k^\nu$ and $k^{1-\nu}$ for any $\nu \in (0,1)$. We prove an information-theoretic lower bound on the relation between the update information size and runtime complexity that shows the asymptotic optimality of our scheme. For $\nu = 1/2$, our constructions outperform Verkle commitments by about a factor of $2$ in terms of both the update information size and runtime, but makes use of larger public parameters.
Yevgeniy Dodis, Daniel Jost, Balachandar Kesavan, Antonio Marcedone
In May 2020, Zoom Video Communications, Inc. (Zoom) announced a multi-step plan to comprehensively support end-to-end encrypted (E2EE) group video calls and subsequently rolled out basic E2EE support to customers in October 2020. In this work we provide the first formal security analysis of Zoom's E2EE protocol, and also lay foundation to the general problem of E2EE group video communication.
We observe that the vast security literature analyzing asynchronous messaging does not translate well to synchronous video calls. Namely, while strong forms of forward secrecy and post compromise security are less important for (typically short-lived) video calls, various liveness properties become crucial. For example, mandating that participants quickly learn of updates to the meeting roster and key, media streams being displayed are recent, and banned participants promptly lose any access to the meeting. Our main results are as follows:
1. Propose a new notion of leader-based continuous group key agreement with liveness, which accurately captures the E2EE properties specific to the synchronous communication scenario. 2. Prove security of the core of Zoom's E2EE meetings protocol in the above well-defined model. 3. Propose ways to strengthen Zoom's liveness properties by simple modifications to the original protocol, which subsequently influenced updates implemented in production.
We observe that the vast security literature analyzing asynchronous messaging does not translate well to synchronous video calls. Namely, while strong forms of forward secrecy and post compromise security are less important for (typically short-lived) video calls, various liveness properties become crucial. For example, mandating that participants quickly learn of updates to the meeting roster and key, media streams being displayed are recent, and banned participants promptly lose any access to the meeting. Our main results are as follows:
1. Propose a new notion of leader-based continuous group key agreement with liveness, which accurately captures the E2EE properties specific to the synchronous communication scenario. 2. Prove security of the core of Zoom's E2EE meetings protocol in the above well-defined model. 3. Propose ways to strengthen Zoom's liveness properties by simple modifications to the original protocol, which subsequently influenced updates implemented in production.
Yi Wang, Rongmao Chen, Xinyi Huang, Moti Yung
Motivated by the violation of two fundamental assumptions in secure communication - receiver-privacy and sender-freedom - by a certain entity referred to as ``the dictator'', Persiano et al. introduced the concept of Anamorphic Encryption (AME) for public key cryptosystems (EUROCRYPT 2022). Specifically, they presented receiver/sender-AME, directly tailored to scenarios where receiver privacy and sender freedom assumptions are compromised, respectively. In receiver-AME, entities share a double key to communicate in anamorphic fashion, raising concerns about the online distribution of the double key without detection by the dictator. The sender-AME with no shared secret is a potential candidate for key distribution. However, the only such known schemes (i.e., LWE and Dual LWE encryptions) suffer from an intrinsic limitation and cannot achieve reliable distribution.
Here, we reformulate the sender-AME, present the notion of $\ell$-sender-AME and formalize the properties of (strong) security and robustness. Robustness refers to guaranteed delivery of duplicate messages to the intended receiver, ensuring that decrypting normal ciphertexts in an anamorphic way or decrypting anamorphic ciphertexts with an incorrect duplicate secret key results in an explicit abort signal. We first present a simple construction for pseudo-random and robust public key encryption that shares the similar idea of public-key stegosystem by von Ahn and Hopper (EUROCRYPT 2004). Then, inspired by Chen et al.'s malicious algorithm-substitution attack (ASA) on key encapsulation mechanisms (KEM) (ASIACRYPT 2020), we give a generic construction for hybrid PKE with special KEM that encompasses well-known schemes, including ElGamal and Cramer-Shoup cryptosystems.
The constructions of $\ell$-sender-AME motivate us to explore the relations between AME, ASA on PKE, and public-key stegosystem. The results show that a strongly secure $\ell$-sender-AME is such a strong primitive that implies reformulated receiver-AME, public-key stegosystem, and generalized ASA on PKE. By expanding the scope of sender-anamorphic encryption and establishing its robustness, as well as exploring the connections among existing notions, we advance secure communication protocols under challenging conditions.
Here, we reformulate the sender-AME, present the notion of $\ell$-sender-AME and formalize the properties of (strong) security and robustness. Robustness refers to guaranteed delivery of duplicate messages to the intended receiver, ensuring that decrypting normal ciphertexts in an anamorphic way or decrypting anamorphic ciphertexts with an incorrect duplicate secret key results in an explicit abort signal. We first present a simple construction for pseudo-random and robust public key encryption that shares the similar idea of public-key stegosystem by von Ahn and Hopper (EUROCRYPT 2004). Then, inspired by Chen et al.'s malicious algorithm-substitution attack (ASA) on key encapsulation mechanisms (KEM) (ASIACRYPT 2020), we give a generic construction for hybrid PKE with special KEM that encompasses well-known schemes, including ElGamal and Cramer-Shoup cryptosystems.
The constructions of $\ell$-sender-AME motivate us to explore the relations between AME, ASA on PKE, and public-key stegosystem. The results show that a strongly secure $\ell$-sender-AME is such a strong primitive that implies reformulated receiver-AME, public-key stegosystem, and generalized ASA on PKE. By expanding the scope of sender-anamorphic encryption and establishing its robustness, as well as exploring the connections among existing notions, we advance secure communication protocols under challenging conditions.
29 November 2023
Zurich, Switzerland, 25 May - 26 May 2024
Event date: 25 May to 26 May 2024
Submission deadline: 16 February 2024
Notification: 30 March 2024
Submission deadline: 16 February 2024
Notification: 30 March 2024
Microsoft Research, Redmond, WA
We are excited to announce an internship opportunity at Microsoft Research focused broadly around cryptography, mathematical modeling, and system design for online trust, safety, and reliability in the age of AI. Our interns will have the opportunity to work on real-world problems alongside other interns, researchers, and engineers.
We are looking for creative thinkers, doers, and problem solvers, who are unafraid to venture outside their comfort zone to find solutions to difficult and messy real-world problems. If you are unsure whether you have appropriate background and match this description, we highly recommend applying anyway!
Apply now at: https://jobs.careers.microsoft.com/global/en/job/1639824
We are looking for creative thinkers, doers, and problem solvers, who are unafraid to venture outside their comfort zone to find solutions to difficult and messy real-world problems. If you are unsure whether you have appropriate background and match this description, we highly recommend applying anyway!
Apply now at: https://jobs.careers.microsoft.com/global/en/job/1639824
Closing date for applications:
Contact: Kim Laine (kim.laine@microsoft.com)
University of St.Gallen, Switzerland
There is an open call for a Postdoc position in the Cyber Security and Applied Cryptograhy research group at the Institute of Computer Science, University of St.Gallen, led by Prof. Katerina Mitrokotsa.
Our research interests are centered around information security and applied cryptography, with the larger goal of safeguarding communications and providing strong privacy guarantees. We are active in several areas, a subset of which include:
The starting date for the position is flexible and come with a very competitive salary. The selection process runs until the suitable candidate has been found. The University of St.Gallen conducts excellent research with international implications. The city of St.Gallen is located one hour from Zurich and offers a high quality of life.
Please apply by 10th December 2023 through the job portal (via link).
Our research interests are centered around information security and applied cryptography, with the larger goal of safeguarding communications and providing strong privacy guarantees. We are active in several areas, a subset of which include:
- Verifiable computation
- Secure, private and distributed aggregation
- Secure multi-party computation
- Privacy-preserving biometric authentication
- Anonymous credentials
- Distributed and privacy-preserving authentication
The starting date for the position is flexible and come with a very competitive salary. The selection process runs until the suitable candidate has been found. The University of St.Gallen conducts excellent research with international implications. The city of St.Gallen is located one hour from Zurich and offers a high quality of life.
Please apply by 10th December 2023 through the job portal (via link).
Closing date for applications:
Contact:
Please apply through the job portal (via link).
Eriane Breu (Administrative matters)
Prof. Katerina Mitrokotsa (Research related questions)
More information: https://jobs.unisg.ch/offene-stellen/postdoc-fellow-in-cryptography-information-security-m-f-d-m-w-d/831c6e8a-e191-48ec-92d5-320b2822a9ab