[Resource Topic] 2023/1786: CASE: A New Frontier in Public-Key Authenticated Encryption

Welcome to the resource topic for 2023/1786

Title:
CASE: A New Frontier in Public-Key Authenticated Encryption

Authors: Shashank Agrawal, Shweta Agrawal, Manoj Prabhakaran, Rajeev Raghunath, Jayesh Singla

Abstract:

We introduce a new cryptographic primitive, called Completely Anonymous Signed Encryption (CASE). CASE is a public-key authenticated encryption primitive, that offers anonymity for senders as well as receivers. A “case-packet” should appear, without a (decryption) key for opening it, to be a blackbox that reveals no information at all about its contents. To decase a case-packet fully - so that the message is retrieved and authenticated - a verifcation key is also required.
Defining security for this primitive is subtle. We present a relatively simple Chosen Objects Attack (COA) security definition. Validating this definition, we show that it implies a comprehensive indistinguishability-preservation definition in the real-ideal paradigm. To obtain the latter definition, we extend the Cryptographic Agents framework of [2, 3] to allow maliciously created objects.
We also provide a novel and practical construction for COA-secure CASE under standard assumptions in public-key cryptography, and in the standard model. We believe CASE can be a staple in future cryptographic libraries, thanks to its robust security guarantees and efficient instantiations based on standard assumptions.

ePrint: https://eprint.iacr.org/2023/1786

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