6,573 research outputs found
Space Efficient Computational Multi-Secret Sharing and Its Applications
In a (t_1,...,t_l)-multi-secret sharing scheme (MSSS), l independent secrets s_1,...,s_l are shared with n parties in such a way that at least t_i parties are required to recover the secret s_i (while s_i remains hidden with fewer shares). We consider the problem of minimizing the share size of MSSS in the challenging setting when there are many secrets to be shared among many parties. To circumvent the information-theoretic lower bound (e.g., Blundo [4]), we focus on the computational setting.
A simple generalization of computational secret sharing (Krawczyk [17]) to multi-secret sharing yields a scheme with share size/overhead scaling linearly in l, the total number of secrets. To beat this linear scaling, we consider constructing MSSS based on a related notion of encryption|dynamic threshold public key encryption (DTPKE)|that enables a sender to dynamically specify a threshold for each ciphertext. None of the existing DTPKE is well-suited for our purpose. Thus, we propose a new construction of a dynamic threshold public key encryption scheme with improved efficiency characteristics. We then give a recursive application of our construction that yields an efficient MSSS with share size only logarithmic in the number of secrets (thus effectively O(log l) as in the common cases, where l and n are polynomially related).
Finally, we describe an application of our space efficient (1,2,...,n-1)-MSSS to a special tool called gradual verifiable secret sharing which is the fundamental building block for general multiparty computation (MPC) with n players that provides fairness without honest majority
Compartment-based and Hierarchical Threshold Delegated Verifiable Accountable Subgroup Multi-signatures
In this paper, we study the compartment-based and hierarchical delegation of signing power of the verifiable accountable subgroup multi-signature (vASM). ASM is a multi-signature in which the participants are accountable for the resulting signature, and the number of participants is not fixed. After Micali et al.’s and Boneh et al.’s ASM schemes, the verifiable-ASM (vASM) scheme with a verifiable group setup and more efficient verification phase was proposed recently. The verifiable group setup in vASM verifies the participants at the group setup phase. In this work, we show that the vASM scheme can also be considered as a proxy signature in which an authorized user (original signer, designator) delegates her signing rights to a single (or a group of) unauthorized user(s) (proxy signer). Namely, we propose four new constructions with the properties and functionalities of an ideal proxy signature and a compartment-based/hierarchical structure. In the first construction, we apply the vASM scheme recursively; in the second one, we use Shamir’s secret sharing (SSS) scheme; in the third construction, we use SSS again but in a nested fashion. In the last one, we use the hierarchical threshold secret sharing (HTSS) scheme for delegation. Then, we show the affiliation of our constructions to proxy signatures and compare our constructions with each other in terms of efficiency and security. Finally we compare the vASM scheme with the existing pairing-based proxy signature schemes
An ideal multi-secret sharing scheme based on minimal privileged coalitions
How to construct an ideal multi-secret sharing scheme for general access
structures is difficult. In this paper, we solve an open problem proposed by
Spiez et al.recently [Finite Fields and Their Application, 2011(17) 329-342],
namely to design an algorithm of privileged coalitions of any length if such
coalitions exist. Furthermore, in terms of privileged coalitions, we show that
most of the existing multi-secret sharing schemes based on Shamir threshold
secret sharing are not perfect by analyzing Yang et al.'s scheme and Pang et
al.'s scheme. Finally, based on the algorithm mentioned above, we devise an
ideal multi-secret sharing scheme for families of access structures, which
possesses more vivid authorized sets than that of the threshold scheme.Comment: 13page
Finding Safety in Numbers with Secure Allegation Escrows
For fear of retribution, the victim of a crime may be willing to report it
only if other victims of the same perpetrator also step forward. Common
examples include 1) identifying oneself as the victim of sexual harassment,
especially by a person in a position of authority or 2) accusing an influential
politician, an authoritarian government, or ones own employer of corruption. To
handle such situations, legal literature has proposed the concept of an
allegation escrow: a neutral third-party that collects allegations anonymously,
matches them against each other, and de-anonymizes allegers only after
de-anonymity thresholds (in terms of number of co-allegers), pre-specified by
the allegers, are reached.
An allegation escrow can be realized as a single trusted third party;
however, this party must be trusted to keep the identity of the alleger and
content of the allegation private. To address this problem, this paper
introduces Secure Allegation Escrows (SAE, pronounced "say"). A SAE is a group
of parties with independent interests and motives, acting jointly as an escrow
for collecting allegations from individuals, matching the allegations, and
de-anonymizing the allegations when designated thresholds are reached. By
design, SAEs provide a very strong property: No less than a majority of parties
constituting a SAE can de-anonymize or disclose the content of an allegation
without a sufficient number of matching allegations (even in collusion with any
number of other allegers). Once a sufficient number of matching allegations
exist, the join escrow discloses the allegation with the allegers' identities.
We describe how SAEs can be constructed using a novel authentication protocol
and a novel allegation matching and bucketing algorithm, provide formal proofs
of the security of our constructions, and evaluate a prototype implementation,
demonstrating feasibility in practice.Comment: To appear in NDSS 2020. New version includes improvements to writing
and proof. The protocol is unchange
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