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PrivacyPreserving Public Auditing for Secure Cloud Storage
 IEEE Trans. Computers
"... Abstract—Using cloud storage, users can remotely store their data and enjoy the ondemand highquality applications and services from a shared pool of configurable computing resources, without the burden of local data storage and maintenance. However, the fact that users no longer have physical poss ..."
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Abstract—Using cloud storage, users can remotely store their data and enjoy the ondemand highquality applications and services from a shared pool of configurable computing resources, without the burden of local data storage and maintenance. However, the fact that users no longer have physical possession of the outsourced data makes the data integrity protection in cloud computing a formidable task, especially for users with constrained computing resources. Moreover, users should be able to just use the cloud storage as if it is local, without worrying about the need to verify its integrity. Thus, enabling public auditability for cloud storage is of critical importance so that users can resort to a thirdparty auditor (TPA) to check the integrity of outsourced data and be worry free. To securely introduce an effective TPA, the auditing process should bring in no new vulnerabilities toward user data privacy, and introduce no additional online burden to user. In this paper, we propose a secure cloud storage system supporting privacypreserving public auditing. We further extend our result to enable the TPA to perform audits for multiple users simultaneously and efficiently. Extensive security and performance analysis show the proposed schemes are provably secure and highly efficient. Our preliminary experiment conducted on Amazon EC2 instance further demonstrates the fast performance of the design. Index Terms—Data storage, privacy preserving, public auditability, cloud computing, delegation, batch verification, zero knowledge Ç 1
Highspeed highsecurity signatures
"... Abstract. This paper shows that a $390 massmarket quadcore 2.4GHz Intel Westmere (Xeon E5620) CPU can create 109000 signatures per second and verify 71000 signatures per second on an elliptic curve at a 2 128 security level. Public keys are 32 bytes, and signatures are 64 bytes. These performance ..."
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Cited by 40 (6 self)
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Abstract. This paper shows that a $390 massmarket quadcore 2.4GHz Intel Westmere (Xeon E5620) CPU can create 109000 signatures per second and verify 71000 signatures per second on an elliptic curve at a 2 128 security level. Public keys are 32 bytes, and signatures are 64 bytes. These performance figures include strong defenses against software sidechannel attacks: there is no data flow from secret keys to array indices, and there is no data flow from secret keys to branch conditions.
Unidirectional ChosenCiphertext Secure Proxy ReEncryption
 In PKC’08, LNCS
"... Abstract. In 1998, Blaze, Bleumer and Strauss introduced a cryptographic primitive called proxy reencryption (PRE) in which a proxy can transform – without seeing the plaintext – a ciphertext encrypted under one key into an encryption of the same plaintext under another key. The concept has recentl ..."
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Cited by 29 (1 self)
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Abstract. In 1998, Blaze, Bleumer and Strauss introduced a cryptographic primitive called proxy reencryption (PRE) in which a proxy can transform – without seeing the plaintext – a ciphertext encrypted under one key into an encryption of the same plaintext under another key. The concept has recently drawn renewed interest. Notably, Canetti and Hohenberger showed how to properly define (and realize) chosenciphertext security for the primitive. Their system is bidirectional as the translation key allows converting ciphertexts in both directions. This paper presents the first unidirectional proxy reencryption schemes with chosenciphertext security in the standard model (i.e. without the random oracle idealization). The first system provably fits a unidirectional extension of the CanettiHohenberger security model. As a second contribution, the paper considers a more realistic adversarial model where attackers may choose dishonest users ’ keys on their own. It is shown how to modify the first scheme to achieve security in the latter scenario. At a moderate expense, the resulting system provides additional useful properties such as noninteractive temporary delegations. Both constructions are efficient and rely on mild complexity assumptions in bilinear groups. Like the CanettiHohenberger scheme, they meet a relaxed flavor of chosenciphertext security introduced by Canetti, Krawczyk and Nielsen. 1
TwoTier Signatures, Strongly Unforgeable Signatures, and FiatShamir without Random Oracles
, 2007
"... We show how the FiatShamir transform can be used to convert threemove identification protocols into twotier signature schemes (a primitive we define) with a proof of security that makes a standard assumption on the hash function rather than modeling it as a random oracle. The result requires secu ..."
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Cited by 23 (1 self)
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We show how the FiatShamir transform can be used to convert threemove identification protocols into twotier signature schemes (a primitive we define) with a proof of security that makes a standard assumption on the hash function rather than modeling it as a random oracle. The result requires security of the starting protocol against concurrent attacks. We can show that numerous protocols have the required properties and so obtain numerous efficient twotier schemes. Our first application is an efficient transform of any unforgeable signature scheme into a strongly unforgeable one, which uses as a tool any twotier scheme. (This extends work of Boneh, Shen and Waters whose transform only applies to a limited class of schemes.) The second application is new onetime signature schemes that, compared to oneway function based ones of the same computational cost, have smaller key and signature sizes.
Lattice Signatures and Bimodal Gaussians
"... Abstract. Our main result is a construction of a latticebased digital signature scheme that represents an improvement, both in theory and in practice, over today’s most efficient lattice schemes. The novel scheme is obtained as a result of a modification of the rejection sampling algorithm that is ..."
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Cited by 14 (3 self)
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Abstract. Our main result is a construction of a latticebased digital signature scheme that represents an improvement, both in theory and in practice, over today’s most efficient lattice schemes. The novel scheme is obtained as a result of a modification of the rejection sampling algorithm that is at the heart of Lyubashevsky’s signature scheme (Eurocrypt, 2012) and several other lattice primitives. Our new rejection sampling algorithm which samples from a bimodal Gaussian distribution, combined with a modified scheme instantiation, ends up reducing the standard deviation of the resulting signatures by a factor that is asymptotically square root in the security parameter. The implementations of our signature scheme for security levels of 128, 160, and 192 bits compare very favorably to existing schemes such as RSA and ECDSA in terms of efficiency. In addition, the new scheme has shorter signature and public key sizes than all previously proposed lattice signature schemes. As part of our implementation, we also designed several novel algorithms which could be of independent interest. Of particular note, is a new algorithm for efficiently generating discrete Gaussian samples over Z n. Current algorithms either require many highprecision floating point exponentiations or the storage of very large precomputed tables, which makes them completely inappropriate for usage in constrained devices. Our sampling algorithm reduces the hardcoded table sizes from linear to logarithmic as compared to the timeoptimal implementations, at the cost of being only a small factor slower. 1
The power of proofsofpossession: securing multiparty signatures against roguekey attacks. Full version of current paper. http://www. cse.ucsd.edu/users/tristenp
"... Abstract. Multiparty signature protocols need protection against roguekey attacks, made possible whenever an adversary can choose its public key(s) arbitrarily. For many schemes, provable security has only been established under the knowledge of secret key (KOSK) assumption where the adversary is ..."
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Cited by 12 (2 self)
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Abstract. Multiparty signature protocols need protection against roguekey attacks, made possible whenever an adversary can choose its public key(s) arbitrarily. For many schemes, provable security has only been established under the knowledge of secret key (KOSK) assumption where the adversary is required to reveal the secret keys it utilizes. In practice, certifying authorities rarely require the strong proofs of knowledge of secret keys required to substantiate the KOSK assumption. Instead, proofs of possession (POPs) are required and can be as simple as just a signature over the certificate request message. We propose a general registered key model, within which we can model both the KOSK assumption and inuse POP protocols. We show that simple POP protocols yield provable security of Boldyreva’s multisignature scheme [11], the LOSSW multisignature scheme [28], and a 2user ring signature scheme due to Bender, Katz, and Morselli [10]. Our results are the first to provide formal evidence that POPs can stop roguekey attacks.
NonInteractive Key Exchange ⋆
"... Abstract Noninteractive key exchange (NIKE) is a fundamental but muchoverlooked cryptographic primitive. It appears as a major contribution in the groundbreaking paper of Diffie and Hellman, but NIKE has remained largely unstudied since then. In this paper, we provide different security models fo ..."
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Cited by 11 (2 self)
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Abstract Noninteractive key exchange (NIKE) is a fundamental but muchoverlooked cryptographic primitive. It appears as a major contribution in the groundbreaking paper of Diffie and Hellman, but NIKE has remained largely unstudied since then. In this paper, we provide different security models for this primitive and explore the relationships between them. We then give constructions for secure NIKE in the Random Oracle Model based on the hardness of factoring and in the standard model based on the hardness of a variant of the decisional Bilinear Diffie Hellman Problem for asymmetric pairings. We also study the relationship between NIKE and public key encryption (PKE), showing that a secure NIKE scheme can be generically converted into an INDCCA secure PKE scheme. This conversion also illustrates the fundamental nature of NIKE in public key cryptography.
On Necessary and Sufficient Conditions for Private Ballot Submission. Cryptology ePrint
 Archive, Report 2012/236, 2012. [BVQ10] Josh Benaloh, Serge Vaudenay, and JeanJacques Quisquater
"... Abstract. We exhibit the precise security guarantees that a public key encryption scheme needs to satisfy to guarantee ballot privacy when used in a large class of voting systems. We also identify new security notions for public key encryption that characterize the number of times that a public key ..."
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Abstract. We exhibit the precise security guarantees that a public key encryption scheme needs to satisfy to guarantee ballot privacy when used in a large class of voting systems. We also identify new security notions for public key encryption that characterize the number of times that a public key can be used in different elections, and show that the most common ballot preparation approach that consists in encrypting the vote and adding a NIZK proof of its validity is sound, even without hardwiring the voter identity in the proof. Our results provide important steps towards proving the privacy of the ballot submission procedure in the widely deployed Helios voting system. 1