*15:42* [PhD][New]
Kwangsu Lee: Efficient Hidden Vector Encryptions and Its Applications
Name: Kwangsu Lee

Topic: Efficient Hidden Vector Encryptions and Its Applications

Category: public-key cryptography

Description: \r\nPredicate encryption is a new paradigm of public key encryption that enables searches on encrypted data. Using the predicate encryption, we can search keywords or attributes on encrypted data without decrypting the ciphertexts. In predicate encryption, a ciphertext is associated with attributes and a token corresponds to a predicate. The token that corresponds to a predicate $f$ can decrypt the ciphertext associated with attributes $\\vect{x}$ if and only if $f(\\vect{x})=1$.\r\n

\r\nHidden vector encryption (HVE) is a special kind of predicate encryption. HVE supports the evaluation of conjunctive equality, comparison, and subset operations between attributes in ciphertexts and attributes in tokens. Currently, several HVE schemes were proposed where the ciphertext size, the token size, and the decryption cost are proportional to the number of attributes in the ciphertext. In this thesis, we consider the efficiency, the generality, and the security of HVE schemes. The results of this thesis are described as follows.\r\n

\r\nThe first results of this thesis are efficient HVE schemes where the token consists of just four group elements and the decryption only requires four bilinear map computations, independent of the number of attributes in the ciphertext. The construction uses composite order bilinear groups and is selectively secure under the well-known assumptions.\r\n

\r\nThe second results are efficient HVE schemes that are secure under any kind of pairing types. To achieve our goals, we proposed a general framework that converts HVE schemes from composite order bilinear groups to prime order bilinear groups. Using the framework, we convert the previous HVE schemes from composite order bilinear groups to prime order bilinear groups.\r\n

\r\nThe third results are fully secure HVE schemes with short tokens. Previous HVE schemes were proven to be secure only in the selective security model where the capabilities of the adversaries are[...]

*15:34* [PhD][New]
Zachary Kissel: Verifiable Symmetric Searchable Encryption
Name: Zachary Kissel

Topic: Verifiable Symmetric Searchable Encryption

Category: secret-key cryptography

Description: Cloud storage has become increasingly prevalent in recent years. It provides a convenient platform for users to store data that can be accessed from anywhere at anytime without the cost of maintaining a storage infrastructure. However, cloud storage is inherently insecure, hindering general acceptance of the paradigm shift. To make use of storage services provided by a cloud, users would need to place their trust, at least implicitly, in the provider. There have been a number of attempts to alleviate the need for this trust through cryptographic methods. An immediate approach would be to encrypt each file before uploading it to the cloud. This approach, calls for a new searching mechanism over encrypted data stored in the cloud.\r\n

\r\nThis dissertation considers a solution to this problem using Symmetric Searchable Encryption (SSE). SSE allows users to offload search queries to the cloud. The cloud is then responsible for returning the encrypted files that match the search queries (also encrypted). Most previous work was focused on keyword search in the Honest-but-Curious (HBC) cloud model, while some more recent work has considered searching on phrases. Recently, a new cloud model was introduced that supersedes the HBC model. This new model, called Semi-Honest but Curious (SHBC), is less restrictive over the actions a cloud can take. In this dissertation, we present three systems that are secure under this new SHBC model. Two systems provide phrase search and the other provides hierarchical access control over keyword search.

[...]

*13:17* [Pub][ePrint]
Efficient Non-Interactive Zero Knowledge Arguments for Set Operations, by Prastudy Fauzi and Helger Lipmaa and Bingsheng Zhang
We propose a non-interactive zero knowledge \\emph{pairwise multiset sum equality test (PMSET)} argument in the common reference string (CRS) model that allows a prover to show that the given committed multisets $\\AAA_j$ for $j \\in \\set{1, 2, 3, 4}$ satisfy $\\AAA_1 \\uplus \\AAA_2 = \\AAA_3 \\uplus \\AAA_4$, i.e., every element is contained in $\\AAA_1$ and $\\AAA_2$ exactly as many times as in $\\AAA_3$ and $\\AAA_4$.As a corollary to the $\\PUTME$ argument, we present arguments that enable to efficiently verify the correctness of various (multi)set operations, for example, that one committed set is the intersection or union of two other committed sets.

The new arguments have constant communication and verification complexity (in group elements and group operations, respectively), whereas the CRS length and the prover\'s computational complexity are both proportional to the cardinality of the (multi)sets.

We show that one can shorten the CRS length at the cost of a small increase of the communication and the verifier\'s computation.

*13:17* [Pub][ePrint]
A Certificate-Based Proxy Signature with Message Recovery without Bilinear Pairing, by Ali Mahmoodi, Javad Mohajeri, Mahmoud Salmasizadeh
In this paper, we propose the first provable secure certificate-based proxy signature with message recovery without bilinear pairing. The notion of certificate-based cryptography was initially introduced by Gentry in 2003, in order to simplify certificate management in traditional public key cryptography(PKC)and to solve the key escrow problem in identity-based cryptosystems. To date, a number of certificate-based proxy signature(CBPS)schemes from bilinear pairing have been proposed. Nonetheless, the total computation cost of a pairing is higher than that of scalar multiplication(e.g., over elliptic curve group). Consequently, schemes without pairings would be more appealing in terms of efficiency. According to the available research in this regard, our scheme is the first provable secure CBPS scheme with message recovery which is based on the elliptic curve discrete logarithm problem. We prove the security of the presented scheme against existential forgery under adaptive chosen message and ID attacks in the random oracle model. Moreover, the paper will also show how it would be possible to convert this scheme to the CBPS scheme without message recovery. This scheme has more applications in situations with limited bandwidth and power-constrained devices.