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191
Security Arguments for Digital Signatures and Blind Signatures
 JOURNAL OF CRYPTOLOGY
, 2000
"... Since the appearance of publickey cryptography in the seminal DiffieHellman paper, many new schemes have been proposed and many have been broken. Thus, the ..."
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Cited by 353 (40 self)
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Since the appearance of publickey cryptography in the seminal DiffieHellman paper, many new schemes have been proposed and many have been broken. Thus, the
An efficient system for nontransferable anonymous credentials with optional anonymity revocation
, 2001
"... Abstract. A credential system is a system in which users can obtain credentials from organizations and demonstrate possession of these credentials. Such a system is anonymous when transactions carried out by the same user cannot be linked. An anonymous credential system is of significant practical r ..."
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Cited by 301 (12 self)
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Abstract. A credential system is a system in which users can obtain credentials from organizations and demonstrate possession of these credentials. Such a system is anonymous when transactions carried out by the same user cannot be linked. An anonymous credential system is of significant practical relevance because it is the best means of providing privacy for users. In this paper we propose a practical anonymous credential system that is based on the strong RSA assumption and the decisional DiffieHellman assumption modulo a safe prime product and is considerably superior to existing ones: (1) We give the first practical solution that allows a user to unlinkably demonstrate possession of a credential as many times as necessary without involving the issuing organization. (2) To prevent misuse of anonymity, our scheme is the first to offer optional anonymity revocation for particular transactions. (3) Our scheme offers separability: all organizations can choose their cryptographic keys independently of each other. Moreover, we suggest more effective means of preventing users from sharing their credentials, by introducing allornothing sharing: a user who allows a friend to use one of her credentials once, gives him the ability to use all of her credentials, i.e., taking over her identity. This is implemented by a new primitive, called circular encryption, which is of independent interest, and can be realized from any semantically secure cryptosystem in the random oracle model.
COCA: A Secure Distributed Online Certification Authority
 ACM TRANSACTIONS ON COMPUTER SYSTEMS
, 2002
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Traffic Analysis: Protocols, Attacks, Design Issues and Open Problems
 PROCEEDINGS OF INTERNATIONAL WORKSHOP ON DESIGN ISSUES IN ANONYMITY AND UNOBSERVABILITY
, 2001
"... We present the traffic analysis problem and expose the most important protocols, attacks and design issues. Afterwards, we propose directions for further research. As we are mostly interested in efficient and practical Internet based protocols, most of the emphasis is placed on mix based constructio ..."
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Cited by 157 (0 self)
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We present the traffic analysis problem and expose the most important protocols, attacks and design issues. Afterwards, we propose directions for further research. As we are mostly interested in efficient and practical Internet based protocols, most of the emphasis is placed on mix based constructions. The presentation is informal in that no complex definitions and proofs are presented, the aim being more to give a thorough introduction than to present deep new insights.
Privacyenhancing technologies for the Internet
"... The increased use of the Internet for everyday activities is bringing new threats to personal privacy. This paper gives an overview of existing and potential privacyenhancing technologies for the Internet, as well as motivation and challenges for future work in this field. ..."
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Cited by 119 (5 self)
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The increased use of the Internet for everyday activities is bringing new threats to personal privacy. This paper gives an overview of existing and potential privacyenhancing technologies for the Internet, as well as motivation and challenges for future work in this field.
Compact ecash
 In EUROCRYPT, volume 3494 of LNCS
, 2005
"... Abstract. This paper presents efficient offline anonymous ecash schemes where a user can withdraw a wallet containing 2 ℓ coins each of which she can spend unlinkably. Our first result is a scheme, secure under the strong RSA and the yDDHI assumptions, where the complexity of the withdrawal and s ..."
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Cited by 119 (20 self)
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Abstract. This paper presents efficient offline anonymous ecash schemes where a user can withdraw a wallet containing 2 ℓ coins each of which she can spend unlinkably. Our first result is a scheme, secure under the strong RSA and the yDDHI assumptions, where the complexity of the withdrawal and spend operations is O(ℓ + k) andtheuser’s wallet can be stored using O(ℓ + k) bits,wherek is a security parameter. The best previously known schemes require at least one of these complexities to be O(2 ℓ · k). In fact, compared to previous ecash schemes, our whole wallet of 2 ℓ coins has about the same size as one coin in these schemes. Our scheme also offers exculpability of users, that is, the bank can prove to third parties that a user has doublespent. We then extend our scheme to our second result, the first ecash scheme that provides traceable coins without a trusted third party. That is, once a user has double spent one of the 2 ℓ coins in her wallet, all her spendings of these coins can be traced. However, the price for this is that the complexity of the spending and of the withdrawal protocols becomes O(ℓ · k) and O(ℓ · k + k 2) bits, respectively, and wallets take O(ℓ · k) bitsofstorage. All our schemes are secure in the random oracle model.
Verifying privacytype properties of electronic voting protocols
"... Electronic voting promises the possibility of a convenient, efficient and secure facility for recording and tallying votes in an election. Recently highlighted inadequacies of implemented systems have demonstrated the importance of formally verifying the underlying voting protocols. We study three p ..."
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Cited by 118 (37 self)
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Electronic voting promises the possibility of a convenient, efficient and secure facility for recording and tallying votes in an election. Recently highlighted inadequacies of implemented systems have demonstrated the importance of formally verifying the underlying voting protocols. We study three privacytype properties of electronic voting protocols: in increasing order of strength, they are voteprivacy, receiptfreeness, and coercionresistance. We use the applied pi calculus, a formalism well adapted to modelling such protocols, which has the advantages of being based on wellunderstood concepts. The privacytype properties are expressed using observational equivalence and we show in accordance with intuition that coercionresistance implies receiptfreeness, which implies voteprivacy. We illustrate our definitions on three electronic voting protocols from the literature. Ideally, these three properties should hold even if the election officials are corrupt. However, protocols that were designed to satisfy receiptfreeness or coercionresistance may not do so in the presence of corrupt officials. Our model and definitions allow us to specify and easily change which authorities are supposed to be trustworthy.
The OneMoreRSAInversion Problems and the Security of Chaum’s Blind Signature Scheme
 Journal of Cryptology
, 2003
"... Abstract We introduce a new class of computational problems which we call the "onemoreRSAinversion " problems. Our main result is that two problems in this class, which we call the chosentarget and knowntarget inversion problems respectively, have polynomiallyequivalent comput ..."
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Cited by 88 (5 self)
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Abstract We introduce a new class of computational problems which we call the &quot;onemoreRSAinversion &quot; problems. Our main result is that two problems in this class, which we call the chosentarget and knowntarget inversion problems respectively, have polynomiallyequivalent computational complexity. We show how this leads to a proof of security for Chaum's RSAbased blind signature scheme in the random oracle model based on the assumed hardness of either of these problems. We define and prove analogous results for &quot;onemorediscretelogarithm &quot; problems. Since the appearence of the preliminary version of this paper, the new problems we have introduced have found other uses as well.
Easy Come  Easy Go Divisible Cash
, 1998
"... Abstract. Recently, there has been an interest in creating practical anonymous electronic cash with the ability to conduct payments of exact amounts, as is typically the practice in physical payment systems. The most general solution for such payments is to allow electronic coins to be divisible (e ..."
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Cited by 77 (1 self)
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Abstract. Recently, there has been an interest in creating practical anonymous electronic cash with the ability to conduct payments of exact amounts, as is typically the practice in physical payment systems. The most general solution for such payments is to allow electronic coins to be divisible (e.g., each coin can be spent incrementally but total purchases are limited to the monetary value of the coin). In Crypto’95, T. Okamoto presented the first efficient divisible, anonymous (but linkable) offline ecash scheme requiring only O(1og n/) computations for each of the withdrawal, payment and deposit procedures, where A / = (total coin value) / (smallest divisible unit) is the divisibility precision. However, the zeroknowledge protocol used for the creation of a blinded unlinkable coin by Okamoto is quite inefficient and is used only at setup to make the system efficient. Incorporating “unlinkable ” blinding only in the setup, however, limits the level of anonymity offered by allowing the linking of all coins withdrawnrather than a more desirable anonymity which allows only linking of subcoins of a withdrawn coin. In this paper we make a further step towards practicality of complete (i.e., divisible) anonymous ecash by presenting a solution where all pre cedures (setup, withdrawal, payment and deposit) are bounded by tens of exponentiations; in particular we improve on Okamoto’s result by 3 orders of magnitude, while the size of the coin remains about 300 Bytes, based on a 512 bit modulus. Moreover, the protocols are compatible with tracing methods used for “fair ” or “revokable ” anonymous cash.
On cryptographic assumptions and challenges
 in Proceedings of IACR CRYPTO
, 2003
"... Abstract. We deal with computational assumptions needed in order to design secure cryptographic schemes. We suggest a classi£cation of such assumptions based on the complexity of falsifying them (in case they happen not to be true) by creating a challenge (competition) to their validity. As an outco ..."
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Cited by 77 (4 self)
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Abstract. We deal with computational assumptions needed in order to design secure cryptographic schemes. We suggest a classi£cation of such assumptions based on the complexity of falsifying them (in case they happen not to be true) by creating a challenge (competition) to their validity. As an outcome of this classi£cation we propose several open problems regarding cryptographic tasks that currently do not have a good challenge of that sort. The most outstanding one is the design of an ef£cient block ciphers. 1 The Main Dilemma Alice and Bob are veteran cryptographers (see Dif£e [15] for their history; apparently RSA [38] is their £rst cooperation). One day, while Bob is sitting in his of£ce his colleague Alice enters and says: “I have designed a new signature scheme. It has an 120 bits long public key and the signatures are 160 bits long”. That’s fascinating, says Bob, but what computational assumption is it based on? Well, says Alice, it is based on a new trapdoor permutation fk and a new hash function h and the assumption that after given fk (but not the trapdoor information) and many pairs of the form (mi, f −1