Identity-based multi-group threshold broadcast encryption

doi:10.1016/j.csi.2026.104169

Identity-based multi-group threshold broadcast encryption

2026-08-01

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DOI：10.1016/j.csi.2026.104169

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Threshold encryption is becoming a significant part in modern cryptography and is standing as a central focus of the upcoming NIST competition. An active branch in this field is Threshold Broadcast Encryption (TBE), which integrates threshold settings into the broadcast encryption paradigm. In a TBE scheme, a sender can arbitrarily select a target set of recipients to encrypt a message; decryption is successful if and only if at least t users within that set collaborate, where t represents the predefined threshold. Despite its utility, existing TBE literature is largely restricted to single-message, single-group scenarios. This constraint makes TBE impractical for modern platforms, such as social media and streaming services, which requires to efficiently deliver diverse content to multiple distinct groups of viewers simultaneously. To address this limitation, we first establish formal definitions for a new primitive: Multi-group Threshold Broadcast Encryption (MTBE), which supports the encryption of one or more messages that are sent to multiple target groups. As a proof of concept, we then propose the first Identity-based MTBE construction. Our scheme achieves constant-size ciphertexts, being independent of the number of recipients or groups. We also implement our proposed scheme to give some concrete benchmarks.

Keywords:

Threshold encryption

Multi-group

Threshold broadcast encryption

Identity-based multi-group threshold broadcast encryption

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