The security of modern public-key cryptography generally relies on computational intractability assumptions, such as integer factorization and discrete logarithm problems. This paper proposes a fundamentally different foundation for security: the intrinsic mathematical properties of tensor product categories—globalentanglement, rigid decomposition, and sensitivity amplification—are directly employed as security resources of the cryptosystem. Within the modular representation category of finite simple groups over finite fields, the private key correspondsto an irreducible modular representation, while the public key was originally conceived as the character vector of a tensor product of that representation. However, this paper reveals a fatal structural vulnerability: because the character ofthe base representation is public, an adversary can fully recover the private keycharacter through trivial division, causing the original security assumption to collapse completely. To address this, the paper accomplishes a paradigm shift from“character-exposure cryptography” to “structure-commitment cryptography,” redefining the public key as a cryptographic commitment to the multiplicity vectorof the tensor product decomposition. Building upon this, the commitment-basedrepresentation recognition problem and the commitment-based tensor product decomposition problem are formalized, and their hardness is argued under both classical and quantum computational models. At the protocol level, it is pointed outthat non-interactive key exchange faces a fundamental obstacle due to the lack ofrepresentation-category homomorphic commitments; consequently, the research focus is shifted to digital signature schemes. The proposed TC-Sig scheme bridges thegap between commitment hiding and multiplicity verification using zero-knowledgeproof techniques, with security reduced to the commitment-based representationrecognition problem in the random oracle model. A feasibility assessment indicatesthat, for candidate groups such as the Mathieu group M12, key generation and commitment computation can be completed within milliseconds, while the introductionof zero-knowledge proofs increases latency to the order of seconds or minutes, making the scheme suitable for low-frequency, high-security scenarios. The security ofthis framework rests on three cornerstones: the classification rigidity of finite simple groups, the one-wayness of commitment schemes, and the non-abelian quantumcomputing barrier, thereby offering a new pathway for post-quantum cryptographyrooted in pure mathematical structure.
A growing number of firms are acquiring large positions in Bitcoin and other digital assets, raising questions about how cryptocurrency exposure affects financial risk. We develop a framework to evaluate the credit risk associated with holding cryptocurrency on corporate balance sheets. Using Bitcoin prices and option-based valuation, we construct pseudo-bonds, synthetic debt instruments backed by digital assets, to calculate yields, leverage ratios, and default probabilities. Cryptocurrency pseudo-bond yields are extremely high and volatile, reflecting cryptocurrency price dynamics. Using daily data from annual samples from 2020 to 2024, we examine correlations between changes in pseudo-bond yields and changes in corporate bond yields across leverage levels. Correlations are generally small once leverage approaches one and above, indicating weak short-run co-movement between crypto-linked credit risk innovations and traditional credit conditions at economically meaningful leverage levels. Our pseudo-bond framework is intended as a transparent screening and comparison device for expressing crypto exposure in credit-market terms.
We present an elementary proof that the asymptotic entropy of a random walk on a countable abelian group is zero when the entropy of the first step of the random walk is finite. Unlike the traditional proof, our approach does not rely on the boundary theory of random walks. To our best knowledge, our direct proof is new even for the group of integers.
Abstract In this article, we show that all cyclic branched covers of a Seifert link have left‐orderable fundamental groups, and therefore admit co‐oriented taut foliations and are not ‐spaces, if and only if it is not an link up to orientation. This leads to a proof of the link conjecture for Seifert links. When is an link up to orientation, we determine which of its canonical ‐fold cyclic branched covers have nonleft‐orderable fundamental groups. In addition, we give a topological proof of Ishikawa's classification of strongly quasi‐positive Seifert links and we determine the Seifert links that are definite, resp., have genus zero, resp. have genus equal to its smooth 4‐ball genus, among others. In the last section, we provide a comprehensive survey of the current knowledge and results concerning the link conjecture.
Biscuit is a recent multivariate signature scheme based on the MPC-in-the-Head paradigm. It has been submitted to the NIST competition for additional signature schemes. Signatures are derived from a zero-knowledge proof of knowledge of the solution of a structured polynomial system. This extra structure enables efficient proofs and compact signatures. This short note demonstrates that it also makes these polynomial systems easier to solve than random ones. As a consequence, the original parameters of Biscuit failed to meet the required security levels and had to be upgraded.
In this article we show that all cyclic branched covers of a Seifert link have left-orderable fundamental groups, and therefore admit co-oriented taut foliations and are not $L$-spaces, if and only if it is not an $ADE$ link up to orientation. This leads to a proof of the $ADE$ link conjecture for Seifert links. When $L$ is an $ADE$ link up to orientation, we determine which of its canonical $n$-fold cyclic branched covers $Σ_n(L)$ have non-left-orderable fundamental groups. In addition, we give a topological proof of Ishikawa's classification of strongly quasipositive Seifert links and we determine the Seifert links that are definite, resp. have genus zero, resp. have genus equal to its smooth $4$-ball genus, among others. In the last section, we provide a comprehensive survey of the current knowledge and results concerning the $ADE$ link conjecture.
Open access
Geometric and Algebraic Topology
Geometric Analysis and Curvature Flows
Organometallic Compounds Synthesis and Characterization
Nicholas Brandt, Dennis Hofheinz, Michael Klooß, Michael Reichle
We construct the first blind signature scheme that achieves all of the following properties simultaneously: – it is tightly secure under a standard (i.e., non-interactive, non-q-type) computational assumption, – it does not require pairings, – it does not rely on generic, non-black-box techniques (like generic NIZK proofs). The third property enables a reasonably efficient solution, and in fact signatures in our scheme comprise 10 group elements and 29 Zp-elements. Our scheme starts from a pairing-based non-blind signature scheme (Abe et al., JoC 2023), and uses recent techniques of Chairattana-Apirom, Tessaro, and Zhu (CRYPTO 2024) to replace the pairings used in this scheme with non-interactive zero-knowledge proofs in the random oracle model. This conversion is not generic or straightforward (also because the mentioned previous works have converted only significantly simpler signature schemes), and we are required to improve upon and innovate existing techniques in several places. As an interesting side note, and unlike previous works, our techniques only require a non-programmable random oracle, and our signature scheme achieves predicate blindness (which means that the user can prove state ments about the signed message during the signing process).
Lennart Braun, Guilhem Castagnos, Ivan Damgård, Fabien Laguillaumie · 7 authors
We present distributed key generation and decryption protocols for an additively homomorphic cryptosystem based on class groups, improving on a similar system proposed by Braun, Damgård, and Orlandi at CRYPTO ‘23. Our key generation is similarly constant round but achieves lower communication complexity than the previous work. This improvement is in part the result of relaxing the reconstruction property required of the underlying integer verifiable secret sharing scheme. This eliminates the reliance on potentially costly proofs of knowledge in unknown order groups. We present a new method to batch zero-knowledge proofs in unknown order groups which strengthens these improvements. We also present a protocol which is proven secure against adaptive adversaries in the single inconsistent player (SIP) model. Our protocols are secure in the universal composability (UC) framework and provide guaranteed output delivery. We demonstrate the relative efficiency of our techniques by presenting the running times and communication costs associated with our implementation of the statically secure protocol and provide a direct comparison with alternate state of the art constructions.
Liqun Chen, Changyu Dong, Christopher J. P. Newton, Yalan Wang
Group signatures and their variants have been widely used in privacy-sensitive scenarios such as anonymous authentication and attestation. In this paper, we present a new post-quantum group signature scheme from symmetric primitives. Using only symmetric primitives makes the scheme less prone to unknown attacks than basing the design on newly proposed hard problems whose security is less well-understood. However, symmetric primitives do not have rich algebraic properties, and this makes it extremely challenging to design a group signature scheme on top of them. It is even more challenging if we want a group signature scheme suitable for real-world applications, one that can support large groups and require few trust assumptions. Our scheme is based on MPC-in-the-head non-interactive zero-knowledge proofs, and we specifically design a novel hash-based group credential scheme, which is rooted in the SPHINCS+ signature scheme but with various modifications to make it MPC (multi-party computation) friendly. The security of the scheme has been proved under the fully dynamic group signature model. We provide an implementation of the scheme and demonstrate the feasibility of handling a group size as large as 2 60 . This is the first group signature scheme from symmetric primitives that supports such a large group size and meets all the security requirements.
While the amount of data produced and accumulated continues to advance at unprecedented rates, protection and concealment of data increase its prominence as a field of scientific study that requires more action. It is essential to protect privacy-sensitive data at every phase; at rest, at run, and while computations are executed on data. The zero-knowledge proof (ZKP) schemes are a cryptographic tool toward this aim. ZKP allows a party to securely ensure the data's authenticity and precision without revealing confidential or privacy-sensitive information during communication or computation. The power of zero-knowledge protocols is based on intractable problems. There is a requirement to design more secure and efficient zero-knowledge proofs. This demand raises the necessity of determining appropriate intractable problems to develop novel ZKP schemes. In this paper, we present a brief outline of ZKP schemes, the connection of these structures to group-theoretic intractable problems, and annotate a list of intractable problems in group theory that can be employed to devise new ZKP schemes.
Ward Beullens, Samuel Dobson, Shuichi Katsumata, Yi-Fu Lai · 5 authors
Abstract We construct an efficient dynamic group signature (or more generally an accountable ring signature) from isogeny and lattice assumptions. Our group signature is based on a simple generic construction that can be instantiated by cryptographically hard group actions such as the CSIDH group action or an MLWE-based group action. The signature is of size $$O(\log N)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>O</mml:mi> <mml:mo>(</mml:mo> <mml:mo>log</mml:mo> <mml:mi>N</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> , where N is the number of users in the group. Our idea builds on the recent efficient OR-proof by Beullens, Katsumata, and Pintore (Asiacrypt’20), where we efficiently add a proof of valid ciphertext to their OR-proof and further show that the resulting non-interactive zero-knowledge proof system is online extractable . Our group signatures satisfy more ideal security properties compared to previously known constructions, while simultaneously having an attractive signature size. The signature size of our isogeny-based construction is an order of magnitude smaller than all previously known post-quantum group signatures (e.g., 6.6 KB for 64 members). In comparison, our lattice-based construction has a larger signature size (e.g., either 126 KB or 89 KB for 64 members depending on the satisfied security property). However, since the $$O(\cdot )$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>O</mml:mi> <mml:mo>(</mml:mo> <mml:mo>·</mml:mo> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> -notation hides a very small constant factor, it remains small even for very large group sizes, say $$2^{20}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mn>2</mml:mn> <mml:mn>20</mml:mn> </mml:msup> </mml:math> .
Secure multiparty computation is a focus of the international cryptographic community. The millionaires problem is the most important problem in secure multiparty computation and is a building block for constructing other secure multiparty computation protocols. Several solutions are available to solve this problem, but except for protocols based on garbled circuits, the existing solutions based on public key cryptosystems are only secure in semihonest models. No solution based on a public key cryptosystem is secure against malicious adversaries. This state restricts the resolution of many secure multiparty computation problems in malicious scenarios. A solution that is secure in malicious models is highly applicable in practical application scenarios and is generally appealing. Therefore, the study of the solution to the millionaires problem in a malicious model is of great theoretical and practical significance. In this work, we propose a multiparty computation protocol for the millionaires problem that is secure in a semihonest model. The proposed protocol is simple and easily understandable. We analyze the possible malicious behaviors in this protocol and use zero-knowledge proof and cut-and-choose techniques to resist possible malicious behaviors and thereby convert the protocol into one that is secure in the malicious model. We prove that the proposed protocol is secure in the malicious model by using the well-accepted ideal-real paradigm. Theoretical efficiency analysis shows that the efficiency of our protocol is at least six times that of existing protocols.
An efficient member revocation mechanism is a desirable feature when group signature schemes are applied in practical scenarios. Revocation methods, such as verifier-local revocation (VLR), provide an efficient member revocation in applications of group signatures. However, VLR-group signatures rely on a weaker security notion. On the other hand, group signature schemes for static groups gain stronger security with the full-anonymity security notion. Even though an outsider sees the secret signing keys of all group members in the full-anonymity, the signer is still anonymous. Achieving the full-anonymity for VLR group signature schemes is challenging due to the structure of secret signing keys. The secret signing keys of those schemes consist of tokens, which are used to manage revocation. The reveal of tokens may destroy the anonymity of the signers. We obtain stronger security for the lattice-based VLR group signature schemes by providing a new key generation method, which outputs revocation tokens without deriving from the members’ secret signing keys. We propose a new group signature scheme from lattices with VLR, which achieves stronger security than the previous related works. To avoid signature forgeries, we suggest a new zero-knowledge proof system that requires signers to validate themselves. Moreover, we output an efficient tracing mechanism.
Russell W. F. Lai, Giulio Malavolta, Viktoria Ronge
In their celebrated work, Groth and Sahai [EUROCRYPT'08, SICOMP' 12] constructed non-interactive zero-knowledge (NIZK) proofs for general bilinear group arithmetic relations, which spawned the entire subfield of structure-preserving cryptography. This branch of the theory of cryptography focuses on modular design of advanced cryptographic primitives. Although the proof systems of Groth and Sahai are a powerful toolkit, their efficiency hits a barrier when the size of the witness is large, as the proof size is linear in that of the witness. In this work, we revisit the problem of proving knowledge of general bilinear group arithmetic relations in zero-knowledge. Specifically, we construct a succinct zero-knowledge argument for such relations, where the communication complexity is logarithmic in the integer and source group components of the witness. Our argument has public-coin setup and verifier and can therefore be turned non-interactive using the Fiat-Shamir transformation in the random oracle model. For the special case of non-bilinear group arithmetic relations with only integer unknowns, our system can be instantiated in non-bilinear groups. In many applications, our argument system can serve as a drop-in replacement of Groth-Sahai proofs, turning existing advanced primitives in the vast literature of structure-preserving cryptography into practically efficient systems with short proofs.
This paper introduces a new capability for group signatures called message-dependent opening . It is intended to weaken the high trust placed on the opener; i.e., no anonymity against the opener is provided by an ordinary group signature scheme. In a group signature scheme with message-dependent opening (GS-MDO), in addition to the opener, we set up an admitter that is not able to extract any user’s identity but admits the opener to open signatures by specifying messages where signatures on the specified messages will be opened by the opener. The opener cannot extract the signer’s identity from any signature whose corresponding message is not specified by the admitter. This paper presents formal definitions of GS-MDO and proposes a generic construction of it from identity-based encryption and adaptive non-interactive zero-knowledge proofs. Moreover, we propose two specific constructions, one in the standard model and one in the random oracle model. Our scheme in the standard model is an instantiation of our generic construction but the message-dependent opening property is bounded. In contrast, our scheme in the random oracle model is not a direct instantiation of our generic construction but is optimized to increase efficiency and achieves the unbounded message-dependent opening property. Furthermore, we also demonstrate that GS-MDO implies identity-based encryption, thus implying that identity-based encryption is essential for designing GS-MDO schemes.