Public Traceability in Threshold Decryption

Tracing techniques have been used to identify users who have leaked their decryption keys in a secure multi-receiver encryption system. In the field of distributed cryptography, where trust is distributed, Boneh et al. extended traitor tracing to the framework of threshold decryption, where a single user doesn’t hold the whole secret to decrypt but needs to collaborate with others. However, the tracing capacity in their collusion-secure codes-based schemes is still centralized: only the authority holding the secret tracing key can perform tracing. In this talk, we will present a generalisation of the bipartite threshold KEM/PKE introduced by Boneh et al. that we call q-partite threshold KEM/PKE. This generalisation allows us to replace the binary collusion-secure codes with q-ary IPP codes that supports public traceability. We will highlight the main properties required by such a threshold scheme to allow traitor tracing and we will present a lattice based construction.