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Fuzzy extractors: How to generate strong keys from biometrics and other noisy data. Technical Report 2003/235, Cryptology ePrint archive, http://eprint.iacr.org, 2006. Previous version appeared at EUROCRYPT 2004
 34 [DRS07] [DS05] [EHMS00] [FJ01] Yevgeniy Dodis, Leonid Reyzin, and Adam
, 2004
"... We provide formal definitions and efficient secure techniques for • turning noisy information into keys usable for any cryptographic application, and, in particular, • reliably and securely authenticating biometric data. Our techniques apply not just to biometric information, but to any keying mater ..."
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Cited by 446 (36 self)
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We provide formal definitions and efficient secure techniques for • turning noisy information into keys usable for any cryptographic application, and, in particular, • reliably and securely authenticating biometric data. Our techniques apply not just to biometric information, but to any keying material that, unlike traditional cryptographic keys, is (1) not reproducible precisely and (2) not distributed uniformly. We propose two primitives: a fuzzy extractor reliably extracts nearly uniform randomness R from its input; the extraction is errortolerant in the sense that R will be the same even if the input changes, as long as it remains reasonably close to the original. Thus, R can be used as a key in a cryptographic application. A secure sketch produces public information about its input w that does not reveal w, and yet allows exact recovery of w given another value that is close to w. Thus, it can be used to reliably reproduce errorprone biometric inputs without incurring the security risk inherent in storing them. We define the primitives to be both formally secure and versatile, generalizing much prior work. In addition, we provide nearly optimal constructions of both primitives for various measures of “closeness” of input data, such as Hamming distance, edit distance, and set difference.
ChosenCiphertext Security from IdentityBased Encryption. Adv
 in Cryptology — Eurocrypt 2004, LNCS
, 2004
"... We propose simple and efficient CCAsecure publickey encryption schemes (i.e., schemes secure against adaptive chosenciphertext attacks) based on any identitybased encryption (IBE) scheme. Our constructions have ramifications of both theoretical and practical interest. First, our schemes give a n ..."
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Cited by 244 (13 self)
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We propose simple and efficient CCAsecure publickey encryption schemes (i.e., schemes secure against adaptive chosenciphertext attacks) based on any identitybased encryption (IBE) scheme. Our constructions have ramifications of both theoretical and practical interest. First, our schemes give a new paradigm for achieving CCAsecurity; this paradigm avoids “proofs of wellformedness ” that have been shown to underlie previous constructions. Second, instantiating our construction using known IBE constructions we obtain CCAsecure encryption schemes whose performance is competitive with the most efficient CCAsecure schemes to date. Our techniques extend naturally to give an efficient method for securing also IBE schemes (even hierarchical ones) against adaptive chosenciphertext attacks. Coupled with previous work, this gives the first efficient constructions of CCAsecure IBE schemes. 1
Plutus: Scalable secure file sharing on untrusted storage
, 2003
"... Plutus is a cryptographic storage system that enables secure file sharing without placing much trust on the file servers. In particular, it makes novel use of cryptographic primitives to protect and share files. Plutus features highly scalable key management while allowing individual users to retain ..."
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Cited by 183 (2 self)
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Plutus is a cryptographic storage system that enables secure file sharing without placing much trust on the file servers. In particular, it makes novel use of cryptographic primitives to protect and share files. Plutus features highly scalable key management while allowing individual users to retain direct control over who gets access to their files. We explain the mechanisms in Plutus to reduce the number of cryptographic keys exchanged between users by using filegroups, distinguish file read and write access, handle user revocation efficiently, and allow an untrusted server to authorize file writes. We have built a prototype of Plutus on OpenAFS. Measurements of this prototype show that Plutus achieves strong security with overhead comparable to systems that encrypt all network traffic.
Practical Verifiable Encryption and Decryption of Discrete Logarithms
, 2003
"... Abstract. This paper addresses the problem of designing practical protocols for proving properties about encrypted data. To this end, it presents a variant of the new public key encryption of Cramer and Shoup based on Paillier’s decision composite residuosity assumption, along with efficient protoco ..."
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Cited by 165 (22 self)
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Abstract. This paper addresses the problem of designing practical protocols for proving properties about encrypted data. To this end, it presents a variant of the new public key encryption of Cramer and Shoup based on Paillier’s decision composite residuosity assumption, along with efficient protocols for verifiable encryption and decryption of discrete logarithms (and more generally, of representations with respect to multiple bases). This is the first verifiable encryption system that provides chosen ciphertext security and avoids inefficient cutandchoose proofs. The presented protocols have numerous applications, including key escrow, optimistic fair exchange, publicly verifiable secret and signature sharing, universally composable commitments, group signatures, and confirmer signatures. 1
Sequences of Games: A Tool for Taming Complexity in Security Proofs
, 2004
"... This paper is brief tutorial on a technique for structuring security proofs as sequences games. ..."
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Cited by 155 (0 self)
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This paper is brief tutorial on a technique for structuring security proofs as sequences games.
On the security of joint signature and encryption
, 2002
"... We formally study the notion of a joint signature and encryption in the publickey setting. We refer to this primitive as signcryption, adapting the terminology of [35]. We present two definitions for the security of signcryption depending on whether the adversary is an outsider or a legal user of t ..."
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Cited by 150 (6 self)
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We formally study the notion of a joint signature and encryption in the publickey setting. We refer to this primitive as signcryption, adapting the terminology of [35]. We present two definitions for the security of signcryption depending on whether the adversary is an outsider or a legal user of the system. We then examine generic sequential composition methods of building signcryption from a signature and encryption scheme. Contrary to what recent results in the symmetric setting [5, 22] might lead one to expect, we show that classical “encryptthensign” (EtS) and “signthenencrypt” (StE) methods are both secure composition methods in the publickey setting. We also present a new composition method which we call “committhenencryptandsign” (CtE&S). Unlike the generic sequential composition methods, CtE&S applies the expensive signature and encryption operations in parallel, which could imply a gain in efficiency over the StE and EtS schemes. We also show that the new CtE&S method elegantly combines with the recent “hashsignswitch” technique of [30], leading to efficient online/offline signcryption. Finally and of independent interest, we discuss the definitional inadequacy of the standard notion of chosen ciphertext (CCA2) security. We suggest a natural and very slight relaxation of CCA2security, which we call generalized CCA2ecurity (gCCA2). We show that gCCA2security suffices for all known uses of CCA2secure encryption, while no longer suffering from the definitional shortcomings of the latter.
Universal Reencryption for Mixnets
 IN PROCEEDINGS OF THE 2004 RSA CONFERENCE, CRYPTOGRAPHER’S TRACK
, 2002
"... We introduce a new cryptographic technique that we call universal reencryption. A conventional cryptosystem that permits reencryption, such as ElGamal, does so only for a player with knowledge of the public key corresponding to a given ciphertext. In contrast, universal reencryption can be don ..."
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Cited by 104 (11 self)
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We introduce a new cryptographic technique that we call universal reencryption. A conventional cryptosystem that permits reencryption, such as ElGamal, does so only for a player with knowledge of the public key corresponding to a given ciphertext. In contrast, universal reencryption can be done without knowledge of public keys. We propose an asymmetric cryptosystem with universal reencryption that is half as efficient as standard ElGamal in terms of computation and storage. While
An Uninstantiable RandomOracleModel Scheme for a HybridEncryption Problem,” Full version of this paper. Available at http://wwwcse.ucsd.edu/users/mihir
"... Abstract. We present a simple, natural randomoracle (RO) model scheme, for a practical goal, that is uninstantiable, meaning is proven in the RO model to meet its goal yet admits no standardmodel instantiation that meets this goal. The goal in question is INDCCApreserving asymmetric encryption w ..."
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Cited by 82 (5 self)
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Abstract. We present a simple, natural randomoracle (RO) model scheme, for a practical goal, that is uninstantiable, meaning is proven in the RO model to meet its goal yet admits no standardmodel instantiation that meets this goal. The goal in question is INDCCApreserving asymmetric encryption which formally captures security of the most common practical usage of asymmetric encryption, namely to transport a symmetric key in such a way that symmetric encryption under the latter remains secure. The scheme is an ElGamal variant, called Hash ElGamal, that resembles numerous existing ROmodel schemes, and on the surface shows no evidence of its anomalous properties. These results extend our understanding of the gap between the standard and RO models, and bring concerns raised by previous work closer to practice by indicating that the problem of ROmodel schemes admitting no secure instantiation can arise in domains where RO schemes are commonly designed. 1
Chosenciphertext security from tagbased encryption. Cryptology ePrint Archive
, 2005
"... Abstract. One of the celebrated applications of IdentityBased Encryption (IBE) is the Canetti, Halevi, and Katz (CHK) transformation from any (selectiveidentity secure) IBE scheme into a full chosenciphertext secure encryption scheme. Since such IBE schemes in the standard model are known from p ..."
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Cited by 66 (13 self)
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Abstract. One of the celebrated applications of IdentityBased Encryption (IBE) is the Canetti, Halevi, and Katz (CHK) transformation from any (selectiveidentity secure) IBE scheme into a full chosenciphertext secure encryption scheme. Since such IBE schemes in the standard model are known from previous work this immediately provides new chosenciphertext secure encryption schemes in the standard model. This paper revisits the notion of TagBased Encryption (TBE) and provides security definitions for the selectivetag case. Even though TBE schemes belong to a more general class of cryptographic schemes than IBE, we observe that (selectivetag secure) TBE is a sufficient primitive for the CHK transformation and therefore implies chosenciphertext secure encryption. We construct efficient and practical TBE schemes and give tight security reductions in the standard model from the Decisional Linear Assumption in gapgroups. In contrast to all known IBE schemes our TBE construction does not directly deploy pairings. Instantiating the CHK transformation with our TBE scheme results in an encryption scheme whose decryption can be carried out in one single multiexponentiation. Furthermore, we show how to apply the techniques gained from the TBE construction to directly design a new Key Encapsulation Mechanism. Since in this case we can avoid the CHK transformation the scheme results in improved efficiency. 1
Publickey broadcast encryption for stateless receivers
 In Digital Rights Management — DRM ’02, volume 2696 of LNCS
, 2002
"... A broadcast encryption scheme allows the sender to securely distribute data to a dynamically changing set of users over an insecure channel. One of the most challenging settings for this problem is that of stateless receivers, where each user is given a fixed set of keys which cannot be updated thro ..."
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Cited by 49 (6 self)
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A broadcast encryption scheme allows the sender to securely distribute data to a dynamically changing set of users over an insecure channel. One of the most challenging settings for this problem is that of stateless receivers, where each user is given a fixed set of keys which cannot be updated through the lifetime of the system. This setting was considered by Naor, Naor and Lotspiech [NNL01], who also present a very efficient “subset difference ” (SD) method for solving this problem. The efficiency of this method (which also enjoys efficient traitor tracing mechanism and several other useful features) was recently improved by Halevi and Shamir [HS02], who called their refinement the “Layered SD ” (LSD) method. Both of the above methods were originally designed to work in the centralized symmetric key setting, where only the trusted designer of the system can encrypt messages to users. On the other hand, in many applications it is desirable not to store the secret keys “online”, or to allow untrusted users to broadcast information. This leads to the question of building a public key broadcast encryption scheme for stateless receivers; in particular, of extending the elegant SD/LSD methods to the public key setting. Naor et al. [NNL01] notice that the natural technique for doing so will result in an enormous public key and very large storage for every user. In fact, [NNL01] pose this question of reducing the public key size and user’s storage as the first open problem of their paper. We resolve this question in the affirmative, by demonstrating that an O(1) size public key can be achieved for both of SD/LSD methods, in addition to the same (small) user’s storage and ciphertext size as in the symmetric key setting. 1