Quantum Algorithms for Attacking Hardness Assumptions in Classical and Post‐Quantum Cryptography

In this survey, the authors review the main quantum algorithms for solving the computational problems that serve as hardness assumptions for cryptosystem. To this end, the authors consider both the currently most widely used classically secure cryptosystems, and the most promising candidates for post-quantum secure cryptosystems. The authors provide details on the cost of the quantum algorithms presented in this survey. The authors furthermore discuss ongoing research directions that can impact quantum cryptanalysis in the future

Proxy Re-Encryption and Re-Signatures from Lattices

Proxy re-encryption (PRE) and Proxy re-signature (PRS) were introduced by Blaze, Bleumer and Strauss [Eurocrypt \u2798]. Basically, PRE allows a semi-trusted proxy to transform a ciphertext encrypted under one key into an encryption of the same plaintext under another key, without revealing the underlying plaintext. Since then, many interesting applications have been explored, and many constructions in various settings have been proposed, while PRS allows a semi-trusted proxy to transform Alice\u27s signature on a message into Bob\u27s signature on the same message, but the proxy cannot produce new valid signature on new messages for either Alice or Bob. Recently, for PRE related progress, Cannetti and Honhenberger [CCS \u2707] defined a stronger notion -- CCA-security and construct a bi-directional PRE scheme. Later on, several work considered CCA-secure PRE based on bilinear group assumptions. Very recently, Kirshanova [PKC \u2714] proposed the first single-hop CCA1-secure PRE scheme based on learning with errors (LWE) assumption. For PRS related progress, Ateniese and Hohenberger [CCS\u2705] formalized this primitive and provided efficient constructions in the random oracle model. At CCS 2008, Libert and Vergnaud presented the first multi-hop uni-directional proxy re-signature scheme in the standard model, using assumptions in bilinear groups. In this work, we first point out a subtle but serious mistake in the security proof of the work by Kirshanova. This reopens the direction of lattice-based CCA1-secure constructions, even in the single-hop setting. Then we construct a single-hop PRE scheme that is proven secure in our new tag-based CCA-PRE model. Next, we construct the first multi-hop PRE construction. Lastly, we also construct the first PRS scheme from lattices that is proved secure in our proposed unified security mode

G6K

G6K is a C++ and Python library that implements several Sieve algorithms to be used in more advanced lattice reduction tasks. It follows the stateful machine framework from: Martin R. Albrecht and Léo Ducas and Gottfried Herold and Elena Kirshanova and Eamonn W. Postlethwaite and Marc Stevens, The General Sieve Kernel and New Records in Lattice Reduction. The article is available in this repository and on eprint

Quantum CNOT Circuits Synthesis for NISQ Architectures Using the Syndrome Decoding Problem

International audienceCurrent proposals for quantum compilers involve the synthesis and optimization of linear reversible circuits and among them CNOT circuits. This class of circuits represents a significant part of the cost of running an entire quantum circuit and therefore we aim at reducing the size of CNOT circuits. In this paper we present a new algorithm for the synthesis of CNOT circuits based on the solution of the syndrome decoding problem. Our method addresses the case of ideal hardware with an all-to-all qubit connectivity and the case of near-term quantum devices with restricted connectivity. Benchmarks show that our algorithm outperforms existing algorithms in both cases of partial and full connectivity

Cloud-based data-sharing scheme using verifiable and CCA-secure re-encryption from indistinguishability obfuscation

A cloud-based re-encryption scheme allows a semi-trusted cloud proxy to convert a ciphertext under delegator\u27s public-key into a ciphertext of delegatee\u27s. However, for an untrusted cloud proxy, as the re-encryption program was outsourced on the cloud, the cloud can debug the program and might have illegal activities in practice, such as monitoring the program executing, returning an incorrect re-encryption ciphertext, or colluding with the participants to obtain the sensitive information. In this work, we propose a construction of cloud-based verifiable re-encryption by incorporating new cryptographic primitives of indistinguishability obfuscation and puncturable pseudorandom functions, which can achieve the master-secret security even if the proxy colludes with the delegatee. Furthermore, our scheme can provide the white-box security in re-encryption procedure to implement the sensitive-data protection in the presence of white-box access, and it resists on chosen-ciphertext attacks in both the first-level encryption and the second-level encryption. The decryption is very efficient since it only requires several symmetric PRF operations, which can be deployed and applied in the light-weight security device such as Mobile Phones (MPs), Wireless Body Area Networks (WBANs) and nodes in Internet-of-Things (IoTs)