International Association for Cryptologic Research

International Association
for Cryptologic Research


CASE: A New Frontier in Public-Key Authenticated Encryption

Shashank Agrawal , Coinbase
Shweta Agrawal , IIT Madras, Chennai, India
Manoj Prabhakaran , IIT Bombay, Mumbai, India
Rajeev Raghunath , IIT Bombay, Mumbai, India
Jayesh Singla , IIT Bombay, Mumbai, India
Search ePrint
Search Google
Presentation: Slides
Conference: TCC 2023
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 verification 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 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.
  title={CASE: A New Frontier in Public-Key Authenticated Encryption},
  author={Shashank Agrawal and Shweta Agrawal and Manoj Prabhakaran and Rajeev Raghunath and Jayesh Singla},