## CryptoDB

### Giuseppe Ateniese

#### Publications

Year
Venue
Title
2016
PKC
2015
EPRINT
2015
EPRINT
2015
EPRINT
2014
EPRINT
2011
PKC
2010
EPRINT
Modern society is increasingly dependent on, and fearful of, the availability of electronic information. There are numerous examples of situations where sensitive data must be  sometimes reluctantly  shared between two or more entities without mutual trust. As often happens, the research community has foreseen the need for mechanisms to enable limited (privacy-preserving) sharing of sensitive information and a number of effective (if not always efficient) solutions have been proposed. Among them, Private Set Intersection techniques are particularly appealing for scenarios where two parties wish to compute an intersection of their respective sets of items without revealing to each other any other information. Thus far, any other information has been interpreted to mean any information about items not in the intersection. In this paper, we motivate the need for Private Set Intersection with stronger privacy properties that include hiding of the set size held by one of the two entities (Client). This new and important privacy feature turns out to be attainable at relative low additional cost. We illustrate a pair of concrete SHI-PSI (Size-Hiding Private Set Intersection) protocols that offer a trade-off between stronger privacy and better efficiency. Both protocols are provably secure under very standard cryptographic assumptions. We demonstrate their practicality via experimental results obtained from a prototype implementation. We also consider size-hiding in a group PSI setting and construct a Group SHI-PSI extension that incurs surprisingly low overhead.
2009
ASIACRYPT
2008
EPRINT
Storage outsourcing is a rising trend which prompts a number of interesting security issues, many of which have been extensively investigated in the past. However, Provable Data Possession (PDP) is a topic that has only recently appeared in the research literature. The main issue is how to frequently, efficiently and securely verify that a storage server is faithfully storing its clients (potentially very large) outsourced data. The storage server is assumed to be untrusted in terms of both security and reliability. (In other words, it might maliciously or accidentally erase hosted data; it might also relegate it to slow or off-line storage.) The problem is exacerbated by the client being a small computing device with limited resources. Prior work has addressed this problem using either public key cryptography or requiring the client to outsource its data in encrypted form. In this paper, we construct a highly efficient and provably secure PDP technique based entirely on symmetric key cryptography, while not requiring any bulk encryption. Also, in contrast with its predecessors, our PDP technique allows outsourcing of dynamic data, i.e, it efficiently supports operations, such as block modification, deletion and append.
2008
EPRINT
Proxy re-encryption (PRE) allows a proxy to convert a ciphertext encrypted under one key into an encryption of the same message under another key. The main idea is to place as little trust and reveal as little information to the proxy as necessary to allow it to perform its translations. At the very least, the proxy should not be able to learn the keys of the participants or the content of the messages it re-encrypts. However, in all prior PRE schemes, it is easy for the proxy to determine between which participants a re-encryption key can transform ciphertexts. This can be a problem in practice. For example, in a secure distributed file system, content owners may want to use the proxy to help re-encrypt sensitive information *without* revealing to the proxy the *identity* of the recipients. In this work, we propose key-private (or anonymous) re-encryption keys as an additional useful property of PRE schemes. We formulate a definition of what it means for a PRE scheme to be secure and key-private. Surprisingly, we show that this property is not captured by prior definitions or achieved by prior schemes, including even the secure *obfuscation* of PRE by Hohenberger, Rothblum, shelat and Vaikuntanathan (TCC 2007). Finally, we propose the first key-private PRE construction and prove its security under a simple extension of the Decisional Bilinear Diffie Hellman assumption and its key-privacy under the Decision Linear assumption in the standard model.
2007
EPRINT
We introduce a model for {\em provable data possession} ($\pdp$) that allows a client that has stored data at an untrusted server to verify that the server possesses the original data without retrieving it. The model generates probabilistic proofs of possession by sampling random sets of blocks from the server, which drastically reduces I/O costs. The client maintains a constant amount of metadata to verify the proof. The challenge/response protocol transmits a small, constant amount of data, which minimizes network communication. Thus, the $\pdp$ model for remote data checking supports large data sets in widely-distributed storage systems. Previous work offers guarantees weaker than data possession, or requires prohibitive overhead at the server. We present two provably-secure $\pdp$ schemes that are more efficient than previous solutions, even when compared with schemes that achieve weaker guarantees. In particular, the overhead at the server is low (or even constant), as opposed to linear in the size of the data. Experiments using our implementation verify the practicality of $\pdp$ and reveal that the performance of $\pdp$ is bounded by disk I/O and not by cryptographic computation.
2006
EPRINT
In \cite{Cao}, a putative framing attack'' against the ACJT group signature scheme \cite{ACJT00} is presented. This note shows that the attack framework considered in \cite{Cao} is \emph{invalid}. As we clearly illustrate, there is \textbf{no security weakness} in the ACJT group signature scheme as long as all the detailed specifications in \cite{ACJT00} are being followed.
2006
EPRINT
In a proxy re-encryption scheme a semi-trusted proxy converts a ciphertext for Alice into a ciphertext for Bob {\em without} seeing the underlying plaintext. A number of solutions have been proposed in the public-key setting. In this paper, we address the problem of Identity-Based proxy re-encryption, where ciphertexts are transformed from one {\it identity} to another. Our schemes are compatible with current IBE deployments and do not require any extra work from the IBE trusted-party key generator. In addition, they are non-interactive and one of them permits multiple re-encryptions. Their security is based on a standard assumption (DBDH) in the random oracle model.
2006
EPRINT
A time-bound hierarchical key assignment scheme is a method to assign time-dependent encryption keys to a set of classes in a partially ordered hierarchy, in such a way that each class can compute the keys of all classes lower down in the hierarchy, according to temporal constraints. In this paper we design and analyze time-bound hierarchical key assignment schemes which are provably-secure and efficient. We consider both the unconditionally secure and the computationally secure settings and distinguish between two different goals: security with respect to key indistinguishability and against key recovery. We first present definitions of security with respect to both goals in the unconditionally secure setting and we show tight lower bounds on the size of the private information distributed to each class. Then, we consider the computational setting and we further distinguish security against static and adaptive adversarial behaviors. We explore the relations between all possible combinations of security goals and adversarial behaviors and, in particular, we prove that security against adaptive adversaries is (polynomially) equivalent to security against static adversaries. Afterwards, we prove that a recently proposed scheme is insecure against key recovery. Finally, we propose two different constructions for time-bound key assignment schemes. The first one is based on symmetric encryption schemes, whereas, the second one makes use of bilinear maps. Both constructions support updates to the access hierarchy with local changes to the public information and without requiring any private information to be re-distributed. These appear to be the first constructions for time-bound hierarchical key assignment schemes which are simultaneously practical and provably-secure.
2005
EPRINT
In 1998, Blaze, Bleumer, and Strauss (BBS) proposed an application called atomic proxy re-encryption, in which a semi-trusted proxy converts a ciphertext for Alice into a ciphertext for Bob without seeing the underlying plaintext. We predict that fast and secure re-encryption will become increasingly popular as a method for managing encrypted file systems. Although efficiently computable, the wide-spread adoption of BBS re-encryption has been hindered by considerable security risks. Following recent work of Ivan and Dodis, we present new re-encryption schemes that realize a stronger notion of security and we demonstrate the usefulness of proxy re-encryption as a method of adding access control to the SFS read-only file system. Performance measurements of our experimental file system demonstrate that proxy re-encryption can work effectively in practice.
2005
EPRINT
We provide a construction for a group signature scheme that is provably secure in a universally composable framework, within the standard model with trusted parameters. Our proposed scheme is fairly simple and its efficiency falls within small factors of the most efficient group signature schemes with provable security in any model (including random oracles). Security of our constructions require new cryptographic assumptions, namely the Strong LRSW, EDH, and Strong SXDH assumptions. Evidence for any assumption we introduce is provided by proving hardness in the generic group model. Our second contribution is the first definition of security for group signatures based on the simulatability of real protocol executions in an ideal setting that captures the basic properties of unforgeability, anonymity, unlinkability, and exculpability for group signature schemes.
2005
EPRINT
In 1998, Blaze, Bleumer, and Strauss (BBS) proposed proxy re-signatures, in which a semi-trusted proxy acts as a translator between Alice and Bob. To translate, the proxy converts a signature from Alice into a signature from Bob on the same message. The proxy, however, does not learn any signing key and cannot sign arbitrary messages on behalf of either Alice or Bob. Since the BBS proposal, the proxy re-signature primitive has been largely ignored, but we show that it is a very useful tool for sharing web certificates, forming weak group signatures, and authenticating a network path. We begin our results by formalizing the definition of security for a proxy re-signature. We next substantiate the need for improved schemes by pointing out certain weaknesses of the original BBS proxy re-signature scheme which make it unfit for most practical applications. We then present two secure proxy re-signature schemes based on bilinear maps. Our first scheme relies on the Computational Diffie-Hellman (CDH) assumption; here the proxy can translate from Alice to Bob and vice-versa. Our second scheme relies on the CDH and 2-Discrete Logarithm (2-DL) assumptions and achieves a stronger security guarantee -- the proxy is only able to translate in one direction. Constructing such a scheme has been an open problem since proposed by BBS in 1998. Furthermore in this second scheme, even if the delegator and the proxy collude, they cannot sign on behalf of the delegatee. Both schemes are efficient and secure in the random oracle model.
2004
EPRINT
This paper analyzes the modified Nyberg-Rueppel signature scheme (mNR), proving it secure in the Generic Group Model (GM). We also show that the security of the mNR signature is equivalent (in the standard model) to that of a twin signature, while achieving computational and bandwidth improvements. As a provably secure signature scheme, mNR is very efficient. We demonstrate its practical relevance by providing an application to the construction of a provably secure, self-certified, identity-based scheme (SCID). SCID schemes combine some of the best features of both PKI-based schemes (functionally trusted authorities, public keys revocable without the need to change identifier strings) and ID-based ones (lower bandwidth requirements). The new SCID scheme matches the performance achieved by the most efficient ones based on the discrete logarithm, while requiring only standard security assumptions in the Generic Group Model.
2004
EPRINT
Chameleon signatures were introduced by Krawczyk and Rabin, being non-interactive signature schemes that provide non-transferability. However, that first construction employs a chameleon hash that suffers from a key exposure problem: The non-transferability property requires willingness of the recipient in consequentially exposing a secret key, and therefore invalidating all signatures issued to the same recipient's public key. To address this key-revocation issue, and its attending problems of key redistribution, storage of state information, and greater need for interaction, an identity-based scheme was proposed in [1], while a fully key-exposure free construction, based on the elliptic curves with pairings, appeared later in [7]. Herein we provide several constructions of exposure-free chameleon hash functions based on different cryptographic assumptions, such as the RSA and the discrete logarithm assumptions. One of the schemes is a novel construction that relies on a single trapdoor and therefore may potentially be realized over a large set of cryptographic groups (where the discrete logarithm is hard).
2003
ASIACRYPT
2003
EPRINT
Chameleon signatures are non-interactive signatures based on a hash-and-sign para\-digm, and similar in efficiency to regular signatures. The distinguishing characteristic of chameleon signatures is that their are non-transferable, with only the designated recipient capable of asserting its validity. In this paper, we introduce the first identity-based chameleon hash function. The general advantages of identity-based cryptography over conventional schemes relative to key distribution are even more pronounced in a chameleon hashing scheme, because the owner of a public key does not necessarily need to retrieve the associated secret key. We use the identity-based chameleon hashing scheme to build the id-based chameleon signature and a novel sealed-bid auction scheme that is robust, communication efficient (bidders send a single message), and secure under a particular trust model.
2002
EPRINT
Group signature schemes enable unlinkably anonymous authentication, in the same fashion that digital signatures provide the basis for strong authentication protocols. This paper introduces the first group signature scheme with constant-size parameters that does not require any group member, including group managers, to know trapdoor secrets. This novel type of group signature scheme allows public parameters to be shared among organizations, and are useful when several distinct groups must interact and exchange information about individuals while protecting their privacy.
2001
EPRINT
A group signature scheme allows any group member to sign on behalf of the group in an anonymous and unlinkable fashion. In the event of a dispute, a designated trusted entity can reveal the identity of the signer. Group signatures are claimed to have many useful applications such as voting and electronic cash. A number of group signature schemes have been proposed to-date. However, in order for the whole group signature concept to become practical and credible, the problem of secure and efficient group member revocation must be addressed. In this paper, we construct a new revocation method for group signatures based on the signature scheme by Ateniese et al. at Crypto 2000. This new method represents an advance in the state-of-the-art since the only revocation schemes proposed thus far are either: 1) based on implicit revocation and the use of fixed time periods, or 2) require the signature size to be linear in the number of revoked members. Our method, in contrast, does not rely on time periods, offers constant-length signatures and constant work for the signer.
2000
CRYPTO