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arXiv:2606.01949

Quantum secure blind decryption with two users

Masahito Hayashi, Yuki Ito

quant-phSubmitted Jun 1, 2026• Announced Jun 2, 2026• 0 citations
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Abstract

We propose two types of protocols for quantum secure blind decryption, involving two users and servers. User 1 holds the encrypted ciphertext. The servers store several indexed keys including the key encrypting the ciphertext. User 2 aims to obtain the decrypted text. The protocols are designed to preserve the following types of secrecy: Users ensure the secrecy of the text from the servers. Servers maintain the secrecy of the keys from the users. Our protocols enable User 2 to obtain the decrypted text while preserving these secrecy requirements. Additionally, the second protocol ensures the secrecy of the key index to identify the key encrypting the ciphertext from the servers, and the second protocol requires two non-commuting servers. Furthermore, we analyze the secrecy of the second protocol under post-attack scenarios, where the two servers communicates with each other after the completion of the protocol. We show that our quantum protocol satisfies the secrecy under these attacks, whereas its classical counterpart fails to do so.

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We propose two types of protocols for quantum secure blind decryption, involving two users and servers. User 1 holds the encrypted ciphertext. The servers store several indexed keys including the key encrypting the ciphertext. User 2 aims to obtain the decrypted text. The protocols are designed to preserve the following types of secrecy: Users ensure the secrecy of the text from the servers. Servers maintain the secrecy of the keys from the users. Our protocols enable User 2 to obtain the decrypted text while preserving these secrecy requirements. Additionally, the second protocol ensures the secrecy of the key index to identify the key encrypting the ciphertext from the servers, and the second protocol requires two non-commuting servers. Furthermore, we analyze the secrecy of the second protocol under post-attack scenarios, where the two servers communicates with each other after the completion of the protocol. We show that our quantum protocol satisfies the secrecy under these attacks, whereas its classical counterpart fails to do so.
A blind decryption scheme enables a user to query decryptions from a decryption server without revealing information about the plain-text message. Such schemes are useful, for example, for the implementation of privacy-preserving encrypted file storages and payment systems. In terms of functionality, blind decryption is close to oblivious transfer. For noiseless channels, information-theoretically secure oblivious transfer is impossible. However, in this paper, we show that this is not the case for blind decryption. We formulate a definition of perfect secrecy of symmetric blind decryption for the following setting: at most one of the scheme participants is a passive adversary (honest-but-curious). We also devise a symmetric blind decryption scheme based on modular arithmetic on a ring Zp2 , where p is a prime, and show that it satisfies our notion of perfect secrecy.
This paper has developed a quantum authentication protocol along with the encryption encapsulation by entangled photon states that are forwarded from a trusted server to two users. It is shown to provide second tier security against impersonation and eavesdropping but with the ease of decryption limited only for two legitimate users. In this process, qutrit photon states are used to identity encryption and a one-way-function containing the phase information of the trits is used for basis selection. The protocol is analyzed to test different eavesdropping strategies and is found to provide unconditional security.
Quantum cyber security aims to examine the communication and computation of security within a distributed quantum network. Two primary security concerns, privacy and anonymity, are typically investigated in quantum computational tasks. Therefore, this study proposes a state-of-the-art, single-server, multi-user anonymous blind quantum computation protocol, wherein the anonymous entanglement shared between the server and user is utilized as a quantum resource for blind quantum computation tasks. The anonymity, blindness, and security analyses demonstrated that the proposed protocol can perform blind quantum computation tasks while maintaining the confidentiality of the user identity. Compared with conventional blind quantum computation protocols, this protocol provides additional security for blind quantum computing and serves as a novel design idea for anonymous quantum cryptography protocols.
Blind quantum computation (BQC) protocol allows a client having partial quantum ability to delegate his quantum computation to a remote quantum server without leaking any information about the input, the output and the intended computation to the server. Several BQC protocols have been proposed, e.g., Li et al. in [1] proposed a triple-server BQC protocol and Xu et al. in [2] proposed a single-server BQC protocol. Though both papers claimed that their protocols can satisfy the requirement of privacy, this paper points out a security loophole in their protocols. With that the server can reveal the private information of the client.
ABSTRACT A three‐party post‐quantum key agreement protocol involves server with two communicating parties securely agreeing on a shared secret key in a way that is resistant to quantum attacks. Once the shared secret key is shared using authenticated key agreement protocol, then user (A), and user (B) can use it for securing communication channel using symmetric‐key encryption AES‐256 algorithm. Although there are few third‐party post‐quantum authenticated and key agreement schemes exist, but the recent studies in this paper illustrates that they are not satisfying properties like unlinkability, anonymity, perfect forward secrecy, and signal leakage attacks. Therefore, the proposed protocol ensures anonymity, unlinkablity, perfect forward secrecy, and resistant against signal leakage attacks. The proposed protocol uses different random numbers for each of sessions and ensures freshness of the session key to maintain forward secrecy. In this protocol, the user (A) only communicates with server, and establish an authenticated session key with user (B) which avoids server overheads. The use of ring learning with errors (RLWE) instead of the simpler learning with errors (LWE) is primarily motivated by the need for efficiency, compactness, and scalability in cryptographic applications. A comparative study, including both performance and security assessments, demonstrates that the proposed design is more secure and efficient.
We present a scheme for quantum secure direct communication with quantum encryption. The two authorized users use repeatedly a sequence of the pure entangled pairs (quantum key) shared for encrypting and decrypting the secret message carried by the traveling photons directly. For checking eavesdropping, the two parties perform the single-photon measurements on some decoy particles before each round. This scheme has the advantage that the pure entangled quantum signal source is feasible at present and any eavesdropper cannot steal the message.