### Samenvatting

We revisit the construction of IND-CCA secure key encapsulation mechanisms (KEM) from public-key encryption schemes (PKE). We give new, tighter security reductions for several constructions. Our main result is an improved reduction for the security of the U⊥̸ -transform of Hofheinz, Hövelmanns, and Kiltz (TCC’17) which turns OW-CPA secure deterministic PKEs into IND-CCA secure KEMs. This result is enabled by a new one-way to hiding (O2H) lemma which gives a tighter bound than previous O2H lemmas in certain settings and might be of independent interest. We extend this result also to the case of PKEs with non-zero decryption failure probability and non-deterministic PKEs. However, we assume that the derandomized PKE is injective with overwhelming probability.

In addition, we analyze the impact of different variations of the U⊥̸ -transform discussed in the literature on the security of the final scheme. We consider the difference between explicit ( U⊥ ) and implicit ( U⊥̸ ) rejection, proving that security of the former implies security of the latter. We show that the opposite direction holds if the scheme with explicit rejection also uses key confirmation. Finally, we prove that (at least from a theoretic point of view) security is independent of whether the session keys are derived from message and ciphertext ( U⊥̸ ) or just from the message ( U⊥̸m ).

In addition, we analyze the impact of different variations of the U⊥̸ -transform discussed in the literature on the security of the final scheme. We consider the difference between explicit ( U⊥ ) and implicit ( U⊥̸ ) rejection, proving that security of the former implies security of the latter. We show that the opposite direction holds if the scheme with explicit rejection also uses key confirmation. Finally, we prove that (at least from a theoretic point of view) security is independent of whether the session keys are derived from message and ciphertext ( U⊥̸ ) or just from the message ( U⊥̸m ).

Originele taal-2 | Engels |
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Titel | Theory of Cryptography - 17th International Conference, TCC 2019, Proceedings |

Redacteuren | Dennis Hofheinz, Alon Rosen |

Plaats van productie | Berlin |

Uitgeverij | Springer |

Hoofdstuk | 3 |

Pagina's | 61-90 |

Aantal pagina's | 30 |

Volume | 2 |

ISBN van elektronische versie | 978-3-030-36033-7 |

ISBN van geprinte versie | 978-3-030-36032-0 |

DOI's | |

Status | Gepubliceerd - 22 nov 2019 |

Evenement | 17th International Conference on Theory of Cryptography, TCC 2019 - Nuremberg, Duitsland Duur: 1 dec 2019 → 5 dec 2019 Congresnummer: 17th |

### Publicatie series

Naam | Lecture notes in computer science |
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Volume | 11892 |

ISSN van geprinte versie | 0302-9743 |

ISSN van elektronische versie | 1611-3349 |

Naam | Security and cryptology |
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Volume | 11892 |

### Congres

Congres | 17th International Conference on Theory of Cryptography, TCC 2019 |
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Verkorte titel | TCC |

Land | Duitsland |

Stad | Nuremberg |

Periode | 1/12/19 → 5/12/19 |

### Vingerafdruk

### Citeer dit

Bindel, N., Hamburg, M., Hövelmanns, K., Hülsing, A., & Persichetti, E. (2019). Tighter proofs of CCA security in the quantum random oracle model. In D. Hofheinz, & A. Rosen (editors),

*Theory of Cryptography - 17th International Conference, TCC 2019, Proceedings*(Vol. 2, blz. 61-90). (Lecture notes in computer science; Vol. 11892), (Security and cryptology; Vol. 11892). Berlin: Springer. https://doi.org/10.1007/978-3-030-36033-7_3