At EUROCRYPT 2012, Libert, Peters and Yung (LPY) proposed the first scalable revocable group signature (R-GS) scheme in the standard model which achieves constant signing/verification costs and other ...costs regarding signers are at most logarithmic in N, where N is the maximum number of group members. However, although the LPY R-GS scheme is asymptotically quite efficient, this scheme is not sufficiently efficient in practice. For example, the signature size of the LPY scheme is roughly 10 times larger than that of an RSA signature (for 160-bit security). In this paper, we propose a compact R-GS scheme secure in the random oracle model that is efficient not only in the asymptotic sense but also in practical parameter settings. We achieve the same efficiency as the LPY scheme in an asymptotic sense, and the signature size is nearly equal to that of an RSA signature (for 160-bit security). It is particularly worth noting that our R-GS scheme has the smallest signature size compared to those of previous R-GS schemes which enable constant signing/verification costs. Our technique, which we call parallel Boneh-Boyen-Shacham group signature technique, helps to construct an R-GS scheme without following the technique used in LPY, i.e., we directly apply the Naor-Naor-Lotspiech framework without using any identity-based encryption.
In the situation where there are one sender and multiple receivers and the sender transmits ciphertexts of correlated plaintexts, a receiver selective opening (RSO) attack for a public key encryption ...(PKE) scheme considers adversaries that can corrupt some of the receivers and get their secret keys and plaintexts. Security against RSO attacks for a PKE scheme ensures confidentiality of ciphertexts of uncorrupted receivers. Simulation-based RSO security against chosen ciphertext attacks (SIM-RSO-CCA) is the strongest security notion in all RSO attack scenarios. Jia, Lu, and Li (2016) 19 proposed the first SIM-RSO-CCA secure PKE scheme. However, their scheme used indistinguishability obfuscation, which is not known to be constructed from any standard computational assumption. In this paper, we give two contributions for constructing SIM-RSO-CCA secure PKE from standard computational assumptions. Firstly, we propose a generic construction of SIM-RSO-CCA secure PKE using an IND-CPA secure PKE scheme and a non-interactive zero-knowledge proof system satisfying one-time simulation soundness. Secondly, we propose an efficient and concrete construction of SIM-RSO-CCA secure PKE based on the decisional Diffie-Hellman (DDH) assumption. Moreover, we give a method for efficiently expanding the plaintext space of the DDH-based construction. By applying this method to the construction, we obtain the first DDH-based SIM-RSO-CCA secure PKE scheme supporting a super-polynomially large plaintext space with compact ciphertexts.
Aggregate signature schemes enable us to aggregate multiple signatures into a single short signature. One of its typical applications is sensor networks, where a large number of users and devices ...measure their environments, create signatures to ensure the integrity of the measurements, and transmit their signed data. However, if an invalid signature is mixed into aggregation, the aggregate signature becomes invalid, thus if an aggregate signature is invalid, it is necessary to identify the invalid signature. Furthermore, we need to deal with a situation where an invalid sensor generates invalid signatures probabilistically. In this paper, we introduce a model of aggregate signature schemes with interactive tracing functionality that captures such a situation, and define its functional and security requirements and propose aggregate signature schemes that can identify all rogue sensors. More concretely, based on the idea of Dynamic Traitor Tracing, we can trace rogue sensors dynamically and incrementally, and eventually identify all rogue sensors of generating invalid signatures even if the rogue sensors adaptively collude. In addition, the efficiency of our proposed method is also sufficiently practical.
In the research area of card-based secure computation, one of the long-standing open problems is a problem proposed by Crépeau and Kilian at CRYPTO 1993. This is to develop an efficient protocol ...using a deck of physical cards that generates uniformly at random a permutation with no fixed points (called a derangement), where the resulting permutation must be secret against the parties in the protocol. All the existing protocols for the problem have a common issue of lacking a guarantee to halt within a finite number of steps. In this paper, we investigate feasibility and infeasibility for the problem where both a uniformly random output and a finite runtime is required. First, we propose a way of reducing the original problem, which is to sample a uniform distribution over an inefficiently large set of the derangements, to another problem of sampling a non-uniform distribution but with a significantly smaller underlying set. This result will be a base of a new approach to the problem. On the other hand, we also give (assuming the abc conjecture), under a certain formal model, an asymptotic lower bound of the number of cards for protocols solving the problem using uniform shuffles only. This result would give a supporting evidence for the necessity of dealing with non-uniform distributions such as in the aforementioned first part of our result.
How to Extend CTRT for AES-256 and AES-192 SHIN, SeongHan; YAMADA, Shota; HANAOKA, Goichiro ...
IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences,
08/2022, Letnik:
E105.A, Številka:
8
Journal Article
Recenzirano
AONT (All-or-Nothing Transform) is a kind of (n, n)-threshold secret sharing scheme that distributes a message m into a set of n shares such that the message m can be reconstructed if and only if n ...shares are collected. At CRYPTO 2000, Desai proposed a simple and faster AONT based on the CTR mode of encryption (called CTRT) and proved its security in the ideal cipher model. Though AES-128, whose key length k = 128 and block length l = 128, can be used in CTRT as a block cipher, AES-256 and AES-192 cannot be used due to its intrinsic restriction of k ≤ l. In this paper, we propose an extended CTRT (for short, XCTRT) suitable for AES-256. By thoroughly evaluating all the tricky cases, we prove that XCTRT is secure in the ideal cipher model under the same CTRT security definition. Also, we discuss the security result of XCTRT in concrete parameter settings. For more flexibility of key length, we propose a variant of XCTRT dealing with l<k ≤ 2l by slightly modifying the construction of the last block. After showing implementation details and performance evaluation of CTRT, XCTRT, and the variant, we can say that our XCTRT and its variant have high-speed encoding and decoding performance and are quite practical enough to be deployed in real-world applications.
In a large-scale information-sharing platform, such as a cloud storage, it is often required to not only securely protect sensitive information but also recover it in a reliable manner. Public-key ...encryption with non-interactive opening (PKENO) is considered as a suitable cryptographic tool for this requirement. This primitive is an extension of public-key encryption which enables a receiver to provide a non-interactive proof which confirms that a given ciphertext is decrypted to some public plaintext. In this paper, we present a Tag-KEM/DEM framework for PKENO. In particular, we define a new cryptographic primitive called a Tag-KEM with non-interactive opening (Tag-KEMNO), and prove the KEM/DEM composition theorem for this primitives, which ensures a key encapsulation mechanism (KEM) and a data encapsulation mechanism (DEM) can be, under certain conditions, combined to form a secure PKENO scheme. This theorem provides a secure way of combining a Tag-KEMNO scheme with a DEM scheme to construct a secure PKENO scheme. Using this framework, we explain the essence of existing constructions of PKENO. Furthermore, we present four constructions of Tag-KEMNO, which yields four PKENO constructions. These PKENO constructions coincide with the existing constructions, thereby we explain the essence of these existing constructions. In addition, our Tag-KEMNO framework enables us to expand the plaintext space of a PKENO scheme. Some of the previous PKENO schemes are only able to encrypt a plaintext of restricted length, and there has been no known way to expand this restricted plaintext space to the space of arbitrary-length plaintexts. Using our framework, we can obtain a PKENO scheme with the unbounded-length plaintext space by modifying and adapting such a PKENO scheme with a bounded-length plaintext space.
While standard signatures provide an efficient mechanism for information certification, the lack of privacy protecting measures makes them unsuitable if sensitive or confidential information is being ...certified. In this paper, we revisit nominative signatures, first introduced by Kim, Park and Won, which provides the functionality and security guarantees required to implement a certification system allowing the user (and not the authority) to control the verifiability of an obtained certificate. Unlike systems based on related primitives, the use of nominative signatures protects the user against authority information leaks and impersonation attacks based on these. We refine the security model of nominative signatures, and propose a new efficient scheme which is provably secure based on the computational Diffie-Hellman problem and the decisional linear problem. To the best of our knowledge, our scheme is the the only nominative signature scheme which is provably secure in the standard model based on standard assumptions. Furthermore, unlike most previous schemes, the proposed scheme provides signatures which hide both the signer and user identity. Hence, through our nominative signature scheme, we achieve an efficient non-transferable user certification scheme with strong security guarantees.
Multi-Input Functional Encryption with Controlled Decryption ATTRAPADUNG, Nuttapong; HANAOKA, Goichiro; HIRANO, Takato ...
IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences,
07/2021, Letnik:
E104.A, Številka:
7
Journal Article
Recenzirano
In this paper, we put forward the notion of a token-based multi-input functional encryption (token-based MIFE) scheme - a notion intended to give encryptors a mechanism to control the decryption of ...encrypted messages, by extending the encryption and decryption algorithms to additionally use tokens. The basic idea is that a decryptor must hold an appropriate decryption token in addition to his secrete key, to be able to decrypt. This type of scheme can address security concerns potentially arising in applications of functional encryption aimed at addressing the problem of privacy preserving data analysis. We firstly formalize token-based MIFE, and then provide two basic schemes; both are based on an ordinary MIFE scheme, but the first additionally makes use of a public key encryption scheme, whereas the second makes use of a pseudorandom function (PRF). Lastly, we extend the latter construction to allow decryption tokens to be restricted to specified set of encryptions, even if all encryptions have been done using the same encryption token. This is achieved by using a constrained PRF.
Machine learning models inherently memorize significant amounts of information, and thus hiding not only prediction processes but also trained models, i.e., model obliviousness, is desirable in the ...cloud setting. Several works achieved model obliviousness with the MNIST dataset, but datasets that include complicated samples, e.g., CIFAR-10 and CIFAR-100, are also used in actual applications, such as face recognition. Secret sharing-based secure prediction for CIFAR-10 is difficult to achieve. When a deep layer architecture such as CNN is used, the calculation error when performing secret calculation becomes large and the accuracy deteriorates. In addition, if detailed calculations are performed to improve accuracy, a large amount of calculation is required. Therefore, even if the conventional method is applied to CNN as it is, good results as described in the paper cannot be obtained. In this paper, we propose two approaches to solve this problem. Firstly, we propose a new protocol named Batch-normalizedActivation that combines BatchNormalization and Activation. Since BatchNormalization includes real number operations, when performing secret calculation, parameters must be converted into integers, which causes a calculation error and decrease accuracy. By using our protocol, calculation errors can be eliminated, and accuracy degradation can be eliminated. Further, the processing is simplified, and the amount of calculation is reduced. Secondly, we explore a secret computation friendly and high accuracy architecture. Related works use a low-accuracy, simple architecture, but in reality, a high accuracy architecture should be used. Therefore, we also explored a high accuracy architecture for the CIFAR10 dataset. Our proposed protocol can compute prediction of CIFAR-10 within 15.05 seconds with 87.36% accuracy while providing model obliviousness.
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