Constructing Identity-Based Revocation Schemes for Efficient Generation of Ciphertexts

Asymmetric broadcast encryption (ABE) allows a sender, given the public keys or identities of recipients, to encrypt a message such that only an authorized subset of users can decrypt it. In fully asymmetric settings, where any user may act as a sender, ciphertext generation time and ciphertext size become critical performance metrics. However, most existing ABE schemes impose substantial sender-side computational costs and scale poorly with system size. This paper presents new ABE constructions that achieve fast ciphertext generation while maintaining compact ciphertexts. Our schemes are built upon the identity-based revocation (IBR) framework, enabling each user's identity to serve directly as a public key. We first propose a basic IBR scheme that produces constant-size ciphertexts independent of the number of recipients or revoked users, achieving efficient encryption through optimized hash-to-point and aggregation techniques. We then extend this design to a tree-based construction that supports large-scale systems and offers a practical trade-off among encryption cost, decryption efficiency, and secret-key size. Both schemes are proven CPA-secure under a modified Decisional Bilinear Diffie–Hellman (mDBDH) assumption in the random-oracle model. Extensive experiments with concrete parameters demonstrate that our schemes significantly outperform existing asymmetric revocation approaches. For a system with 106users and a revocation rate of 1:5–3%, prior schemes require tens of seconds to generate a ciphertext, whereas our constructions complete encryption within 1:6 seconds while keeping the ciphertext size nearly constant (below 102KB).