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International Conference on Data Security and Privacy Protection (DSPP)

Improved AB-CPREs with HRA Security

Yu Zhang, Yang Wang, Mingqiang Wang

Published Oct 16, 2023• 2 citations
Publisher

Abstract

Attribute-based conditional proxy re-encryption (AB-CPRE) schemes offer flexible controls over delegations of decryption rights, and offer an efficient solution for enforcing access control on outsourced encrypted datum. Recently, Liang et al. proposed the first lattice-based AB-CPREs with selective attribute security against chosen-plaintext attacks (CPA) in ESORICS 2021. In this paper, we first show how to construct a CPA secure AB-CPRE scheme which is suitable for circuits in NC $^{1}$ with polynomially bounded parameters. By contrast, schemes proposed by Liang et al. are only suitable for circuits in NC $^{0}$ with similar parameters. We then show how to convert our CPA secure AB-CPREs to be secure against honest re-encryption attacks (HRA) under a more reasonable definition. We could show that the CPA security and the HRA security of our schemes are based on standard LWE assumptions for suitable parameters in the standard model.

DOI
10.1109/dspp58763.2023.10404893

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Attribute-based conditional proxy re-encryption (AB-CPRE) schemes offer flexible controls over delegations of decryption rights, and offer an efficient solution for enforcing access control on outsourced encrypted datum. Recently, Liang et al. proposed the first lattice-based AB-CPREs with selective attribute security against chosen-plaintext attacks (CPA) in ESORICS 2021. In this paper, we first show how to construct a CPA secure AB-CPRE scheme which is suitable for circuits in NC 1^{1}1 with polynomially bounded parameters. By contrast, schemes proposed by Liang et al. are only suitable for circuits in NC 0^{0}0 with similar parameters. We then show how to convert our CPA secure AB-CPREs to be secure against honest re-encryption attacks (HRA) under a more reasonable definition. We could show that the CPA security and the HRA security of our schemes are based on standard LWE assumptions for suitable parameters in the standard model.
Attribute‐based conditional proxy re‐encryption protocols (AB‐CPREs) enable a delegator to delegate his decryption rights via different policies and grant the data owner greater flexibility in allocating their encrypted private data stored in the cloud. However, existing lattice‐based AB‐CPREs suffer from some drawbacks such as large parameters and weak passive securities. To the best of our knowledge, the first quantum‐safe key‐policy AB‐CPREs with polynomially bounded parameters (for certain NC 0 circuits/policies) that is selective attribute secure against honest re‐encryption attacks (HRA) is presented. The security of our proposed AB‐CPREs is based on standard LWE assumptions. We further introduce the directly revocable AB‐CPREs, a primitive that enables a delegator to authorize and revoke his delegation of decryption rights dynamically and offers more flexible access control on externally stored encrypted data. Definition and security model of single‐hop directly revocable AB‐CPREs are given, and the first detailed construction of single‐hop directly revocable AB‐CPREs based on standard LWE assumptions is also proposed.
Proxy re-encryption (PRE) is a momentous and widely used cryptographic technique. It enables a proxy to forward ciphertext without the need of decryption. PRE has received significant interest in applications like cloud computing, blockchain, and the Internet of Things. Despite its wide range of uses, PRE has also been subject to new security and privacy regulations. In PKC’19, Cohen et al.et~al.et al.~first drew attention to the weakness in PRE's security against chosen-plaintext attacks (CPA) and put up a more stringent security concept known as security against honest re-encryption attacks (HRA). Notably, Cohen provides a beneficial conclusion as well. It is proveded that PRE schemes with re-encryption simulatability property can be elevated from CPA to HRA security. It is also proved that CPA-secure PRE schemes with re-encryption simulatability property can be directly elevated to those satisfying HRA security. However, those PRE schemes with re-encryption simulatability are almost always based on pairings. In this study, to the best of our knowledge, we directly construct HRA-secure PRE with re-encryption simulatability for the first time based on the learning with errors (LWE) assumption, which was widely believed to be quantum-resistant. Based on the re-encryption key generation algorithm and the re-encryption algorithm construction method of the above scheme, we can modify attribute-based conditional proxy re-encryption (AB-CPRE) as well as the corresponding attribute-based proxy re-encryption (AB-PRE) algorithm to make them have re-encryption simulatability properties. Finally, by using this property, We boost the security of AB-CPRE scheme of ESORICS'21 from CPA to HRA and simplify the HRA-security proof for the AB-PRE of ESORICS'21.
Proxy re-encryption (PRE) schemes, which nicely solve the problem of delegating decryption rights, enable a semi-trusted proxy to transform a ciphertext encrypted under one key into a ciphertext of the same message under another arbitrary key. Cohen first pointed out the insufficiency of the security under chosen-plaintext attacks (CPA) of PREs in PKC 2019, and proposed a strictly stronger security notion, named security under honest re-encryption attacks (HRA), of PREs. Surprisingly, a few PREs satisfy the stronger HRA security and almost all of them are paring-based till now. To the best of our knowledge, we present the first direct construction of HRA secure single-hop PREs based on standard LWE problems with comparably small and polynomially-bounded parameters in this paper. Combing known reductions, the HRA security of our PREs could also be guaranteed by the worst-case basic lattice problems (e.g. SIVPγ with γ=Õ(n3.5)). Our single-hop PRE schemes are key-private, which means that the implicit identities of a re-encryption key will not be revealed even in the case of a proxy colluding with some corrupted users. Meanwhile, our single-hop PRE schemes are also post-compromise (PCS) secure, ensuring that a re-encrypted ciphertext remains confidential even when the past key, potential old ciphertexts and the re-encryption key have been exposed. Some discussions about key-privacy of multi-hop PREs are also proposed, which indicates that several constructions of multi-hop PREs do not satisfy their key-privacy definitions.
In a proxy re-encryption system, a semi-trusted proxy can convert a ciphertext originally intended for Alice into one encrypting the same plaintext for Bob without seeing the underlying plaintext.However, a fine-grained delegation is demanded in some scenarios.For this, Weng et al. introduce the notion of conditional proxy re-encryption (CPRE), and formalize its security model and propose an efficient CPRE scheme.This paper presents the notion of identity-based multi-condition proxy re-encryption, which is a variant of identity-based condition proxy re-encryption.In such system, ciphertexts are generated under specified conditions by Alice, and the proxy can translate the ciphertext if the relevant conditions are satisfied.We formalize its security model and construct a concrete multi-condition proxy re-encryption scheme, and prove its security in the standard model.
Ciphertext policy attribute-based encryption (CP-ABE) is a promising cryptographic technology that provides fine-grained access control as well as data confidentiality. It enables one sender to encrypt the data for more receivers, and to specify a policy on who can decrypt the ciphertext using his/her attributes alone. However, most existing ABE schemes are constructed on bilinear maps and they cannot resist quantum attacks. In this paper, we propose a multi-authority CP-ABE (MA-CPABE) scheme on ideal lattices which is still secure in post-quantum era. On one hand, multiple attribute authorities are required when user's attributes cannot be managed by a central authority. On the other hand, compared with generic lattice, the ideal lattice has extra algebraic structure and can be used to construct more efficient cryptographic applications. By adding some virtual attributes for each authority, our scheme can support flexible threshold access policy. Security analysis shows that the proposed scheme is secure against chosen plaintext attack (CPA) in the standard model under the ring learning with errors (R-LWE) assumption.
As an extension to conditional proxy re-encryption, fuzzy conditional proxy re-encryption allows for a proxy to re-encrypt a ciphertext only if it satisfies some t-out-of-d threshold condition. Therefore, it is more desirable in some applications where fine-grained control of the decryption delegation is required. In this paper, we construct the first lattice-based fuzzy conditional proxy re-encryption scheme as a post-quantum alternative to this primitive. In our construction, original ciphertexts and re-encryption ciphertexts have the same form, thus only one decryption algorithm is needed for both kinds of ciphertexts. We formalize its security model and prove that it is selective secure under the LWE assumption.