[Resource Topic] 2022/1146: A Sponge-Based PRF with Good Multi-user Security

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Title:
A Sponge-Based PRF with Good Multi-user Security

Authors: Arghya Bhattacharjee, Ritam Bhaumik, Mridul Nandi

Abstract:

Both multi-user PRFs and sponge-based constructions have generated a lot of research interest lately. Dedicated analyses for multi-user security have improved the bounds a long distance from the early generic bounds obtained through hybrid arguments, yet the bounds generally don’t allow the number of users to be more than birthday-bound in key-size. Similarly, known sponge constructions suffer from being only birthday-bound secure in terms of their capacity.
We present in this paper \textsf{Muffler}, a multi-user PRF built from a random permutation using a full-state sponge with feed-forward, which uses a combination of the user keys and unique user IDs to solve both the problems mentioned by improving the security bounds for multi-user constructions and sponge constructions. For D construction query blocks and T permutation queries, with key-size \kappa = n/2 and tag-size \tau = n/2 (where n is the state-size or the size of the underlying permutation), both D and T must touch birthday bound in n in order to distinguish \textsf{Muffler} from a random function.

ePrint: https://eprint.iacr.org/2022/1146

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