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Anamorphic Signatures: Secrecy from a Dictator Who Only Permits Authentication!

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Advances in Cryptology – CRYPTO 2023 (CRYPTO 2023)

Part of the book series: Lecture Notes in Computer Science ((LNCS,volume 14082))

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Abstract

The goal of this research is to raise technical doubts regarding the usefulness of the repeated attempts by governments to curb Cryptography (aka the “Crypto Wars”), and argue that they, in fact, cause more damage than adding effective control. The notion of Anamorphic Encryption was presented in Eurocrypt’22 for a similar aim. There, despite the presence of a Dictator who possesses all keys and knows all messages, parties can arrange a hidden “anamorphic” message in an otherwise indistinguishable from regular ciphertexts (wrt the Dictator).

In this work, we postulate a stronger cryptographic control setting where encryption does not exist (or is neutralized) since all communication is passed through the Dictator in, essentially, cleartext mode (or otherwise, when secure channels to and from the Dictator are the only confidentiality mechanism). Messages are only authenticated to assure recipients of the identity of the sender. We ask whether security against the Dictator still exists, even under such a strict regime which allows only authentication (i.e., authenticated/ signed messages) to pass end-to-end, and where received messages are determined by/ known to the Dictator, and the Dictator also eventually gets all keys to verify compliance of past signing. To frustrate the Dictator, this authenticated message setting gives rise to the possible notion of anamorphic channels inside signature and authentication schemes, where parties attempt to send undetectable secure messages (or other values) using signature tags which are indistinguishable from regular tags. We define and present implementation of schemes for anamorphic signature and authentication; these are applicable to existing and standardized signature and authentication schemes which were designed independently of the notion of anamorphic messages. Further, some cornerstone constructions of the foundations of signatures, in fact, introduce anamorphism.

The extended version of this paper, including extra results and proofs, is available as [17].

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Acknowledgment

The first and the last author have been supported by the National Centre for Research and Development (Warsaw), project ESCAPE PL-TW/VII/5/2020.

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Authors and Affiliations

  1. Wrocław University of Science and Technology, Wrocław, Poland

    Mirosław Kutyłowski & Marcin Zawada

  2. Università di Salerno, Fisciano, Italy

    Giuseppe Persiano

  3. Google LLC, New York City, USA

    Giuseppe Persiano & Moti Yung

  4. Telecom Paris, Institut Polytechnique de Paris, Palaiseau, France

    Duong Hieu Phan

  5. Columbia University, New York, USA

    Moti Yung

  6. NASK -National Research Institute, Warsaw, Poland

    Mirosław Kutyłowski

Authors
  1. Mirosław Kutyłowski
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  2. Giuseppe Persiano
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  3. Duong Hieu Phan
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  4. Moti Yung
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  5. Marcin Zawada
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Correspondence to Mirosław Kutyłowski .

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Editors and Affiliations

  1. Rambus Inc., San Jose, CA, USA

    Helena Handschuh

  2. Brown University, Providence, RI, USA

    Anna Lysyanskaya

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Kutyłowski, M., Persiano, G., Phan, D.H., Yung, M., Zawada, M. (2023). Anamorphic Signatures: Secrecy from a Dictator Who Only Permits Authentication!. In: Handschuh, H., Lysyanskaya, A. (eds) Advances in Cryptology – CRYPTO 2023. CRYPTO 2023. Lecture Notes in Computer Science, vol 14082. Springer, Cham. https://doi.org/10.1007/978-3-031-38545-2_25

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  • DOI: https://doi.org/10.1007/978-3-031-38545-2_25

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