International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Semi-Quantum Tokenized Signatures

Omri Shmueli , Tel Aviv University
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Conference: CRYPTO 2022
Abstract: Quantum tokenized signature schemes (Ben-David and Sattath, QCrypt 2017) allow a sender to generate and distribute quantum unclonable states which grant their holder a one-time permission to sign in the name of the sender. Such schemes are a strengthening of public-key quantum money schemes, as they allow to execute a quantum money scheme where some channels of communication in the system can be made classical. An even stronger primitive is semi-quantum tokenized signatures, where the sender is classical and can delegate the generation of the token to a (possibly malicious) quantum receiver. Semi-quantum tokenized signature schemes imply a powerful version of public-key quantum money satisfying two key features: \begin{itemize} \item The bank is classical and the scheme can execute on a completely classical communication network. In addition, the bank is \emph{stateless} and after the creation of a banknote, does not hold any information nor trapdoors except the balance of accounts in the system. Such quantum money scheme solves the main open problem presented by Radian and Sattath (AFT 2019). \item Furthermore, the classical-communication transactions between users in the system are \emph{direct} and do not need to go through the bank. This enables the transactions to be both classical and private. \end{itemize} While fully-quantum tokenized signatures (where the sender is quantum and generates the token by itself) are known based on quantum-secure indistinguishability obfuscation and injective one-way functions, the semi-quantum version is not known under any computational assumption. In this work we construct a semi-quantum tokenized signature scheme based on quantum-secure indistinguishability obfuscation and the sub-exponential hardness of the Learning with Errors problem. In the process, we show new properties of quantum coset states and a new hardness result on indistinguishability obfuscation of classical subspace membership circuits.
  title={Semi-Quantum Tokenized Signatures},
  author={Omri Shmueli},