Paper 2024/1119

Generic Anamorphic Encryption, Revisited: New Limitations and Constructions

Dario Catalano, University of Catania
Emanuele Giunta, IMDEA Software, Universidad Politécnica de Madrid
Francesco Migliaro, University of Catania
Abstract

The notion of Anamorphic Encryption (Persiano et al. Eurocrypt 2022) aims at establishing private communication against an adversary who can access secret decryption keys and influence the chosen messages. Persiano et al. gave a simple, black-box, rejection sampling-based technique to send anamorphic bits using any IND-CPA secure scheme as underlying PKE. In this paper however we provide evidence that their solution is not as general as claimed: indeed there exists a (contrived yet secure) PKE which lead to insecure anamorphic instantiations. Actually, our result implies that such stateless black-box realizations of AE are impossible to achieve, unless weaker notions are targeted or extra assumptions are made on the PKE. Even worse, this holds true even if one resorts to powerful non-black-box techniques, such as NIZKs, $ i\mathcal{O} $ or garbling. From a constructive perspective, we shed light those required assumptions. Specifically, we show that one could bypass (to some extent) our impossibility by either considering a weaker (but meaningful) notion of AE or by assuming the underlying PKE to (always) produce high min-entropy ciphertexts. Finally, we prove that, for the case of Fully-Asymmetric AE, $ i\mathcal{O}$ can actually be used to overcome existing impossibility barriers. We show how to use $ i\mathcal{O} $ to build Fully-Asymmetric AE (with small anamorphic message space) generically from any IND-CPA secure PKE with sufficiently high min-entropy ciphertexts. Put together our results provide a clearer picture of what black-box constructions can and cannot achieve.

Metadata
Available format(s)
PDF
Category
Foundations
Publication info
Preprint.
Keywords
Anamorphic EncryptionObfuscationImpossibilityBlack-Box Constructions
Contact author(s)
catalano @ dmi unict it
emanuele giunta @ imdea org
francesco migliaro @ phd unict it
History
2024-07-10: approved
2024-07-09: received
See all versions
Short URL
https://ia.cr/2024/1119
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2024/1119,
      author = {Dario Catalano and Emanuele Giunta and Francesco Migliaro},
      title = {Generic Anamorphic Encryption, Revisited: New Limitations and Constructions},
      howpublished = {Cryptology ePrint Archive, Paper 2024/1119},
      year = {2024},
      note = {\url{https://eprint.iacr.org/2024/1119}},
      url = {https://eprint.iacr.org/2024/1119}
}
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