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67
A Secure and Optimally Efficient MultiAuthority Election Scheme
, 1997
"... Abstract. In this paper we present a new multiauthority secretballot election scheme that guarantees privacy, universal verifiability, and robustness. It is the first scheme for which the performance is optimal in the sense that time and communication complexity is minimal both for the individual ..."
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Cited by 217 (6 self)
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Abstract. In this paper we present a new multiauthority secretballot election scheme that guarantees privacy, universal verifiability, and robustness. It is the first scheme for which the performance is optimal in the sense that time and communication complexity is minimal both for the individual voters and the authorities. An interesting property of the scheme is that the time and communication complexity for the voter is independent of the number of authorities. A voter simply posts a single encrypted message accompanied by a compact proof that it contains a valid vote. Our result is complementary to the result by Cramer, Franklin, Schoenmakers, and Yung in the sense that in their scheme the work for voters is linear in the number of authorities but can be instantiated to yield informationtheoretic privacy, while in our scheme the voterâ€™s effort is independent of the number of authorities but always provides computational privacyprotection. We will also point out that the majority of proposed voting schemes provide computational privacy only (often without even considering the lack of informationtheoretic privacy), and that our new scheme is by far superior to those schemes. 1
Efficient threshold signature, multisignature and blind signature schemes based on the GapDiffieHellmanGroup signature scheme
 PROCEEDINGS OF PKC 2003, VOLUME 2567 OF LNCS
, 2003
"... We propose a robust proactive threshold signature scheme, a multisignature scheme and a blind signature scheme which work in any Gap DiffieHellman (GDH) group (where the Computational DiffieHellman problem is hard but the Decisional DiffieHellman problem is easy). Our constructions are based on t ..."
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Cited by 157 (0 self)
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We propose a robust proactive threshold signature scheme, a multisignature scheme and a blind signature scheme which work in any Gap DiffieHellman (GDH) group (where the Computational DiffieHellman problem is hard but the Decisional DiffieHellman problem is easy). Our constructions are based on the recently proposed GDH signature scheme of Boneh et al. [8]. Due to the instrumental structure of GDH groups and of the base scheme, it turns out that most of our constructions are simpler, more efficient and have more useful properties than similar existing constructions. We support all the proposed schemes with proofs under the appropriate computational assumptions, using the corresponding notions of security.
COCA: A Secure Distributed Online Certification Authority
 ACM Transactions on Computer Systems
"... this article, is such an online CA ..."
Efficient generation of shared RSA keys
 Advances in Cryptology  CRYPTO 97
, 1997
"... We describe efficient techniques for a number of parties to jointly generate an RSA key. At the end of the protocol an RSA modulus N = pq is publicly known. None of the parties know the factorization of N. In addition a public encryption exponent is publicly known and each party holds a share of the ..."
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Cited by 124 (4 self)
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We describe efficient techniques for a number of parties to jointly generate an RSA key. At the end of the protocol an RSA modulus N = pq is publicly known. None of the parties know the factorization of N. In addition a public encryption exponent is publicly known and each party holds a share of the private exponent that enables threshold decryption. Our protocols are efficient in computation and communication. All results are presented in the honest but curious settings (passive adversary).
Robust Threshold DSS Signatures
, 1996
"... . We present threshold DSS (Digital Signature Standard) signatures where the power to sign is shared by n players such that for a given parameter t ! n=2 any subset of 2t + 1 signers can collaborate to produce a valid DSS signature on any given message, but no subset of t corrupted players can forg ..."
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Cited by 122 (12 self)
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. We present threshold DSS (Digital Signature Standard) signatures where the power to sign is shared by n players such that for a given parameter t ! n=2 any subset of 2t + 1 signers can collaborate to produce a valid DSS signature on any given message, but no subset of t corrupted players can forge a signature (in particular, cannot learn the signature key). In addition, we present a robust threshold DSS scheme that can also tolerate n=3 players who refuse to participate in the signature protocol. We can also endure n=4 maliciously faulty players that generate incorrect partial signatures at the time of signature computation. This results in a highly secure and resilient DSS signature system applicable to the protection of the secret signature key, the prevention of forgery, and increased system availability. Our results significantly improve over a recent result by Langford from CRYPTO'95 that presents threshold DSS signatures which can stand much smaller subsets of corrupted player...
Simplified VSS and Fasttrack Multiparty Computations with Applications to Threshold Cryptography
, 1998
"... The goal of this paper is to introduce a simple verifiable secret sharing scheme, to improve the efficiency of known secure multiparty protocols and, by employing these techniques, to improve the efficiency of applications which use these protocols. First we present a very simple Verifiable Secret ..."
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Cited by 84 (5 self)
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The goal of this paper is to introduce a simple verifiable secret sharing scheme, to improve the efficiency of known secure multiparty protocols and, by employing these techniques, to improve the efficiency of applications which use these protocols. First we present a very simple Verifiable Secret Sharing protocol which is based on fast cryptographic primitives and avoids altogether the need for expensive zeroknowledge proofs. This is followed by a highly simplified protocol to compute multiplications over shared secrets. This is a major component in secure multiparty computation protocols and accounts for much of the complexity of proposed solutions. Using our protocol as a plugin unit in known protocols reduces their complexity. We show how to achieve efficient multiparty computations in the computational model, through the application of homomorphic commitments. Finally, we present fasttrack multiparty computation protocols. In a model in which malicious faults are rare we s...
A Simplified Approach to Threshold and Proactive RSA
 In Proceedings of CRYPTO
"... We present a solution to both the robust threshold RSA and proactive RSA problems. Our solutions are conceptually simple, and allow for an easy design of the system. The signing key, in our solution, is shared at all times in additive form, which allows for simple signing and for a particularly ..."
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Cited by 83 (1 self)
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We present a solution to both the robust threshold RSA and proactive RSA problems. Our solutions are conceptually simple, and allow for an easy design of the system. The signing key, in our solution, is shared at all times in additive form, which allows for simple signing and for a particularly efficient and straightforward refreshing process for proactivization. The key size is (up to a very small constant) the size of the RSA modulus, and the protocol runs in constant time, even when faults occur, unlike previous protocols where either the size of the key has a linear blowup (at best) in the number of players or the run time of the protocol is linear in the number of faults. The protocol is optimal in its resilience as it can tolerate a minority of faulty players.
Robust and Efficient Sharing of RSA Functions
, 1996
"... We present two efficient protocols which implement robust threshold RSA signature schemes, where the power to sign is shared by N players such that any subset of more then T signers can collaborate to produce a valid RSA signature on any given message, but no subset of fewer than T corrupted players ..."
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Cited by 79 (11 self)
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We present two efficient protocols which implement robust threshold RSA signature schemes, where the power to sign is shared by N players such that any subset of more then T signers can collaborate to produce a valid RSA signature on any given message, but no subset of fewer than T corrupted players can forge a signature. Our protocols are robust in the sense that the correct signature is computed even if up to T players behave in arbitrarily malicious way during the signature protocol. This in particular includes the cases of players that refuse to participate or that generate incorrect partial signatures. Our protocols achieve fault tolerance T of N=2, which is optimal. Our protocols are also very efficient, as the computation performed by each player is comparable to the computation cost of a single RSA signature. Robust threshold signature schemes have very important applications, since they provide increased security and availability for a signing server (e.g. a certification auth...
Asynchronous Verifiable Secret Sharing and Proactive Cryptosystems
 in Proc. 9th ACM Conference on Computer and Communications Security (CCS
, 2002
"... Verifiable secret sharing is an important primitive in distributed cryptography. With the growing interest in the deployment of threshold cryptosystems in practice, the traditional assumption of a synchronous network has to be reconsidered and generalized to an asynchronous model. This paper prop ..."
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Cited by 56 (8 self)
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Verifiable secret sharing is an important primitive in distributed cryptography. With the growing interest in the deployment of threshold cryptosystems in practice, the traditional assumption of a synchronous network has to be reconsidered and generalized to an asynchronous model. This paper proposes the first practical verifiable secret sharing protocol for asynchronous networks. The protocol creates a discrete logarithmbased sharing and uses only a quadratic number of messages in the number of participating servers. It yields the first asynchronous Byzantine agreement protocol in the standard model whose efficiency makes it suitable for use in practice. Proactive cryptosystems are another important application of verifiable secret sharing. The second part of this paper introduces proactive cryptosystems in asynchronous networks and presents an efficient protocol for refreshing the shares of a secret key for discrete logarithmbased sharings.
Verifiable encryption, group encryption, and their applications to group signatures and signature sharing schemes
, 2000
"... Abstract. We generalize and improve the security and efficiency ofthe verifiable encryption scheme ofAsokan et al., such that it can rely on more general assumptions, and can be proven secure without assuming random oracles. We extend our basic protocol to a new primitive called verifiable group enc ..."
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Cited by 51 (8 self)
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Abstract. We generalize and improve the security and efficiency ofthe verifiable encryption scheme ofAsokan et al., such that it can rely on more general assumptions, and can be proven secure without assuming random oracles. We extend our basic protocol to a new primitive called verifiable group encryption. We show how our protocols can be applied to construct group signatures, identity escrow, and signature sharing schemes from a wide range of signature, identification, and encryption schemes already in use. In particular, we achieve perfect separability for all these applications, i.e., all participants can choose their signature and encryption schemes and the keys thereofindependent ofeach other, even without having these applications in mind. 1