Existing semantically secure public-key searchable encryption schemes take search time linear with the total number of the ciphertexts. This makes retrieval from large-scale databases prohibitive. To alleviate this problem, this paper proposes searchable public-key ciphertexts with hidden structures (SPCHS) for keyword search as fast as possible without sacrificing semantic security of the encrypted keywords. In SPCHS, all keyword-searchable ciphertexts are structured by hidden relations, and with the search trapdoor corresponding to a keyword, the minimum information of the relations is disclosed to a search algorithm as the guidance to find all matching ciphertexts efficiently. We construct an SPCHS scheme from scratch in which the ciphertexts have a hidden star-like structure. We prove our scheme to be semantically secure in the random oracle (RO) model. The search complexity of our scheme is dependent on the actual number of the ciphertexts containing the queried keyword, rather than the number of all ciphertexts. Finally, we present a generic SPCHS construction from anonymous identity-based encryption and collision-free full-identity malleable identity-based key encapsulation mechanism (IBKEM) with anonymity. We illustrate two collision-free full-identity malleable IBKEM instances, which are semantically secure and anonymous, respectively, in the RO and standard models. The latter instance enables us to construct an SPCHS scheme with semantic security in the standard model.
Following the seminal work on PEKS, Abdalla. @cite_24 fills some gaps w.r.t. consistency for PEKS and deals with the transformations among primitives related to PEKS. Some efforts have also been devoted to make PEKS versatile. The work of this kind includes conjunctive search @cite_17 @cite_18 @cite_27 @cite_26 @cite_20 @cite_39 , range search @cite_41 @cite_28 @cite_8 , subset search @cite_8 , time-scope search @cite_24 @cite_40 , similarity search @cite_31 , authorized search @cite_47 @cite_30 , equality test between heterogeneous ciphertexts @cite_4 , and fuzzy keyword search @cite_9 . In addition, @cite_37 proposed a PEKS scheme to keep the privacy of keyword search trapdoors.
@cite_30 @cite_18 @cite_26 @cite_47 @cite_4 @cite_37 @cite_8 @cite_41 @cite_28 @cite_9 @cite_39 @cite_24 @cite_27 @cite_40 @cite_31 @cite_20 @cite_17
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In a public key setting, Alice encrypts an email with the public key of Bob, so that only Bob will be able to learn the contents of the email. Consider a scenario where the computer of Alice is infected and unbeknown to Alice it also embeds a malware into the message. Bob's company, Carol, cannot scan his email for malicious content as it is encrypted so the burden is on Bob to do the scan. This is not efficient. We construct a mechanism that enables Bob to provide trapdoors to Carol such that Carol, given an encrypted data and a malware signature, is able to check whether the encrypted data contains the malware signature, without decrypting it. We refer to this mechanism as public-key encryption with delegated search (PKEDS). We formalize PKEDS and give a construction based on ElGamal public-key encryption (PKE). The proposed scheme has ciphertexts which are both searchable and decryptable. This property of the scheme is crucial since an entity can search the entire content of the message, in contrast to existing searchable public-key encryption schemes where the search is done only in the metadata part. We prove in the standard model that the scheme is ciphertext indistinguishable and trapdoor indistinguishable under the Symmetric External Diffie-Hellman (SXDH) assumption. We prove also the ciphertext one-wayness of the scheme under the modified Computational Diffie-Hellman (mCDH) assumption. We show that our PKEDS scheme can be used in different applications such as detecting encrypted malware and forwarding encrypted email. We study the setting in which a user stores encrypted documents (e.g. e-mails) on an untrusted server. In order to retrieve documents satisfying a certain search criterion, the user gives the server a capability that allows the server to identify exactly those documents. Work in this area has largely focused on search criteria consisting of a single keyword. If the user is actually interested in documents containing each of several keywords (conjunctive keyword search) the user must either give the server capabilities for each of the keywords individually and rely on an intersection calculation (by either the server or the user) to determine the correct set of documents, or alternatively, the user may store additional information on the server to facilitate such searches. Neither solution is desirable; the former enables the server to learn which documents match each individual keyword of the conjunctive search and the latter results in exponential storage if the user allows for searches on every set of keywords. We study the problem of a public key encryption with conjunctive keyword search (PECK). The keyword searchable encryption enables a user to outsource his data to the storage of an untrusted server and to have the ability to selectively search his data without leaking information. The PECK scheme provides the document search containing each of several keywords over a public key setting. First, we construct an efficient PECK scheme whose security is proven over a decisional linear Diffie-Hellman assumption in the random oracle model. In comparison with previous schemes, our scheme has the shortest ciphertext size and private key size, and requires a comparable computation overhead. Second, we discuss problems related to the security proof of previous schemes and show they cannot guarantee complete security. Finally, we introduce a new concept called a multi-user PECK scheme, which can achieve an efficient computation and communication overhead and effectively manage the storage in a server for a number of users. When outsourcing data to third-party servers, searchable encryption is an important enabling technique which simultaneously allows the data owner to keep his data in encrypted form and the third-party servers to search in the ciphertexts. Motivated by an encrypted email retrieval and archive scenario, we investigate asymmetric searchable encryption (ASE) schemes which support two special features, namely message recovery and flexible search authorization. With this new primitive, a data owner can keep his data encrypted under his public key and assign different search privileges to third-party servers. In the security model, we define the standard IND-CCA security against any outside attacker and define adapted ciphertext indistinguishability properties against inside attackers according to their functionalities. Moreover, we take into account the potential information leakage from trapdoors, and define two trapdoor security properties. Employing the bilinear property of pairings and a deliberately-designed double encryption technique, we present a provably secure instantiation of the primitive based on the DLIN and BDH assumptions in the random oracle model. We present a (probabilistic) public key encryption (PKE) scheme such that when being implemented in a bilinear group, anyone is able to check whether two ciphertexts are encryptions of the same message. Interestingly, bilinear map operations are not required in key generation, encryption or decryption procedures of the PKE scheme, but is only required when people want to do an equality test (on the encrypted messages) between two ciphertexts that may be generated using different public keys. We show that our PKE scheme can be used in different applications such as searchable encryption and partitioning encrypted data. Moreover, we show that when being implemented in a non-bilinear group, the security of our PKE scheme can be strengthened from One-Way CCA to a weak form of IND-CCA. Asymmetric searchable encryption allows searches to be carried over ciphertexts, through delegation, and by means of trapdoors issued by the owner of the data. Public Key Encryption with Keyword Search (PEKS) is a primitive with such functionality that provides delegation of exact-match searches. As it is important that ciphertexts preserve data privacy, it is also important that trapdoors do not expose the user’s search criteria. The difficulty of formalizing a security model for trapdoor privacy lies in the verification functionality, which gives the adversary the power of verifying if a trapdoor encodes a particular keyword. In this paper, we provide a broader view on what can be achieved regarding trapdoor privacy in asymmetric searchable encryption schemes, and bridge the gap between previous definitions, which give limited privacy guarantees in practice against search patterns. Since it is well-known that PEKS schemes can be trivially constructed from any Anonymous IBE scheme, we propose the security notion of Key Unlinkability for IBE, which leads to strong guarantees of trapdoor privacy in PEKS, and we construct a scheme that achieves this security notion. We construct public-key systems that support comparison queries (x ≥ a) on encrypted data as well as more general queries such as subset queries (x∈ S). Furthermore, these systems support arbitrary conjunctive queries (P1 ∧ ... ∧ Pl) without leaking information on individual conjuncts. We present a general framework for constructing and analyzing public-key systems supporting queries on encrypted data. We introduce the concept of Anonymous Multi-Attribute Encryption with Range Query and Conditional Decryption (AMERQCD). In AMERQCD, a plaintext is encrypted under a point in multidimensional space. To a computationally bounded adversary, the ciphertext hides both the plaintext and the point under which it is encrypted. In a range query, a master key owner releases the decryption key for an arbitrary hyper-rectangle in space, thus allowing decryption of ciphertexts previously encrypted under any point within the hyper-rectangle. However, a computationally bounded adversary cannot learn any information on ciphertexts outside the range covered by the decryption key (except the fact that they do not lie within this range). We give an efficient construction based on the Decision Bilinear Diffie-Hellman (D-BDH) and Decision Linear (D-Linear) assumption. We design an encryption scheme called multi-dimensional range query over encrypted data (MRQED), to address the privacy concerns related to the sharing of network audit logs and various other applications. Our scheme allows a network gateway to encrypt summaries of network flows before submitting them to an untrusted repository. When network intrusions are suspected, an authority can release a key to an auditor, allowing the auditor to decrypt flows whose attributes (e.g., source and destination addresses, port numbers, etc.) fall within specific ranges. However, the privacy of all irrelevant flows are still preserved. We formally define the security for MRQED and prove the security of our construction under the decision bilinear Diffie-Hellman and decision linear assumptions in certain bilinear groups. We study the practical performance of our construction in the context of network audit logs. Apart from network audit logs, our scheme also has interesting applications for financial audit logs, medical privacy, untrusted remote storage, etc. In particular, we show that MRQED implies a solution to its dual problem, which enables investors to trade stocks through a broker in a privacy-preserving manner. Public-key encryption with keyword search (PEKS) is a versatile tool. It allows a third party knowing the search trapdoor of a keyword to search encrypted documents containing that keyword without decrypting the documents or knowing the keyword. However, it is shown that the keyword will be compromised by a malicious third party under a keyword guess attack (KGA) if the keyword space is in a polynomial size. We address this problem with a keyword privacy enhanced variant of PEKS referred to as public-key encryption with fuzzy keyword search (PEFKS). In PEFKS, each keyword corresponds to an exact keyword search trapdoor and a fuzzy keyword search trapdoor. Two or more keywords share the same fuzzy keyword trapdoor. To search encrypted documents containing a specific keyword, only the fuzzy keyword search trapdoor is provided to the third party, i.e., the searcher. Thus, in PEFKS, a malicious searcher can no longer learn the exact keyword to be searched even if the keyword space is small. We propose a universal transformation which converts any anonymous identity-based encryption (IBE) scheme into a secure PEFKS scheme. Following the generic construction, we instantiate the first PEFKS scheme proven to be secure under KGA in the case that the keyword space is in a polynomial size. We study the problem of searching on data that is encrypted using a public key system. Consider user Bob who sends email to user Alice encrypted under Alice’s public key. An email gateway wants to test whether the email contains the keyword “urgent” so that it could route the email accordingly. Alice, on the other hand does not wish to give the gateway the ability to decrypt all her messages. We define and construct a mechanism that enables Alice to provide a key to the gateway that enables the gateway to test whether the word “urgent” is a keyword in the email without learning anything else about the email. We refer to this mechanism as Public Key Encryption with keyword Search. As another example, consider a mail server that stores various messages publicly encrypted for Alice by others. Using our mechanism Alice can send the mail server a key that will enable the server to identify all messages containing some specific keyword, but learn nothing else. We define the concept of public key encryption with keyword search and give several constructions. We identify and fill some gaps with regard to consistency (the extent to which false positives are produced) for public-key encryption with keyword search (PEKS). We define computational and statistical relaxations of the existing notion of perfect consistency, show that the scheme of [7] is computationally consistent, and provide a new scheme that is statistically consistent. We also provide a transform of an anonymous IBE scheme to a secure PEKS scheme that, unlike the previous one, guarantees consistency. Finally we suggest three extensions of the basic notions considered here, namely anonymous HIBE, public-key encryption with temporary keyword search, and identity-based encryption with keyword search. We present two provably secure and efficient schemes for performing conjunctive keyword searches over symmetrically encrypted data. Our first scheme is based on Shamir Secret Sharing and provides the most efficient search technique in this context to date. Although the size of its trapdoors is linear in the number of documents being searched, we empirically show that this overhead remains reasonable in practice. Nonetheless, to address this limitation we provide an alternative based on bilinear pairings that yields constant size trapdoors. This latter construction is not only asymptotically more efficient than previous secure conjunctive keyword search schemes in the symmetric setting, but incurs significantly less storage overhead. Additionally, unlike most previous work, our constructions are proven secure in the standard model. In this paper we explore restricted delegation of searches on encrypted audit logs. We show how to limit the exposure of private information stored in the log during such a search and provide a technique to delegate searches on the log to an investigator. These delegated searches are limited to authorized keywords that pertain to specific time periods, and provide guarantees of completeness to the investigator. Moreover, we show that investigators can efficiently find all relevant records, and can authenticate retrieved records without interacting with the owner of the log. In addition, we provide an empirical evaluation of our techniques using encrypted logs consisting of approximately 27,000 records of IDS alerts collected over a span of a few months. In this paper, we consider the problem of predicate encryption and focus on the predicate for testing whether the Hamming distance between the attribute X of a data item and a target V is equal to (or less than) a threshold t where X and V are of length m. Existing solutions either do not provide attribute protection or produce a big ciphertext of size O(2 m ). For the equality version of the problem, we provide a scheme which is match-concealing (MC) secure and the sizes of the ciphertext and token are both O(m). For the inequality version of the problem, we give a practical scheme, also achieving MC security, which produces a ciphertext with size (O(m^ t_ max ) ) if the maximum value of t, t max , is known in advance and is a constant. We also show how to update the ciphertext if the user wants to increase t max without constructing the ciphertext from scratch. A keyword-searchable encryption scheme allows a user with a "trapdoor" for a keyword to efficiently retrieve some of encrypted data containing the specific keyword over a remote server. The scheme for keyword-searchable encryption is considered as one of crucial building blocks that solves the security problems of privacy and data confidentiality in many settings, such as outsourced database systems and mail (or file) servers. However, most existing schemes support only a single keyword for searching, but do not allow for boolean combinations of keywords. It makes the use of schemes impractical in real applications. To address this problem, we propose an efficient construction for conjunctive keyword-searchable encryption, in which the size of trapdoors is almost same as that for searching a single keyword. Our construction is proven secure against adaptive chosen-keyword attacks in the random oracle model under the external co-Diffie-Hellman assumption. Compared to previous works, our construction has much better performance in terms of both computational and communication cost. In a public key encryption, we may want to enable someone to test whether something is a keyword in a given document without leaking anything else about the document. An email gateway, for example, may be desired to test whether the email contains a keyword “urgent” so that it could route the email accordingly, without leaking any content to the gateway. This mechanism was referred as public key encryption with keyword search [4]. Similarly, a user may want to enable an email gateway to search keywords conjunctively, such as “urgent” email from “Bob” about “finance”, without leaking anything else about the email. We refer to this mechanism as public key encryption with conjunctive field keyword search. In this paper, we define the security model of this mechanism and propose two efficient schemes whose security is proved in the random oracle model.