Adaptively Secure Broadcast Encryption with Forward Secrecy.

Rishab Goyal, Saikumar Yadugiri

Xinwen Zhang, Shangping Wang, Wenpeng Zhang

Motivated by an identity-based broadcast encryption scheme from lattice(1) and a forward-secure identity-based encryption scheme(2), we propose a forward-secure identity-based broadcast encryption scheme from lattice by adding the forward-security mechanism on broadcast encryption scheme. Our scheme satisfies the security requirements of both the broadcast encrypt ion scheme and forward-security scheme, that is, it is forward-secure for the secret keys used previously, and we prove that it is semantic secure based on LWE (Learning With Error)assumption(3) in the random oracle model. In addition, our construction is believed to be secure against quantum computer.

Ran Cohen, Juan A. Garay, Vassilis Zikas

Martin Hirt, Vassilis Zikas

Ran Canetti, Shai Halevi, Jonathan I. Katz

Abstract. Adaptively-secure encryption schemes ensure secrecy even in the presence of an adversary who can corrupt parties in an adaptive manner based on public keys, ciphertexts, and secret data of alreadycorrupted parties. Ideally, an adaptively-secure encryption scheme should, like standard public-key encryption, allow arbitrarily-many parties to use a single encryption key to securely encrypt arbitrarily-many messages to a given receiver who maintains only a single short decryption key. However, it is known that these requirements are impossible to achieve: no non-interactive encryption scheme that supports encryption of an unbounded number of messages and uses a single, unchanging decryption key can be adaptively secure. Impossibility holds even if secure data erasure is possible. We show that this limitation can be overcome by updating the decryption key over time and making some mild assumptions about the frequency of communication between parties. Using this approach, we construct adaptively-secure, completely non-interactive encryption schemes supporting secure encryption of arbitrarily-many messages from arbitrarilymany senders. Our schemes additionally provide forward security and security against chosen-ciphertext attacks. 1

Pete Rigas

We examine public broadcast, forward conceptual, and backward conceptual, Quantum channels in the context of communication protocols that are independent of secret keys. Given research directions of interest previously identified in arXiv: 1804.01797, besides converse upper bounds on the bit transmission rate obtained by the author in recent work (arXiv: 2507.03035), additional possibilities remain, including: (1) determining whether aspects of QKD dependent protocols can be incorporated into steps of QKD independent protocols; (2) whether there would be any amplification to the Quantum-classical performance gap that Alice and Bob can exploit towards prospective Quantum advantage; (3) formulating the conditions under which secrecy and authentication can be simultaneously achieved. To characterize the conditions for which secrecy can be achieved with high probability, we argue that there not only exists suitable protocols which enable Alice and Bob to map into the authenticated space of bit codewords with high probability, but also that forward conceptual channels, through cascading, can significantly increase Eve's probability of false acceptance. Albeit the fact that secrecy, along with conceputalizations of the public broadcast channel, were initially discussed by Maurer for QKD dependent protocols, determining whether aspects of such protocols can be adapted for unconditional security without the use of a secret key is of great interest to explore. We demonstrate that Eve's error probability, through the cascading procedure, can be analyzed with the Holevo information under an optimal decoder. Furthermore, through post-processing of the outputs of a Completely Positive Trace Preserving (CPTP) map, we also demonstrate how to decrease Holevo sum quantities with data-processing and entropy-continuity bounds.