CCA Secure A Posteriori Openable Encryption in the Standard Model

Xavier Bultel (1)

1 SDS - Sécurité des Données et des Systèmes

A Posteriori Openable Public Key Encryptions (APOPKE) allow any user to generate a constant-size key that decrypts the messages they have sent over a chosen period of time. As an important feature, the period can be dynamically chosen after the messages have been sent. This primitive was introduced in 2016 by Bultel and Lafourcade. They also defined the Chosen-Plaintext Attack (CPA) security for APOPKE, and designed a scheme called GAPO, which is CPA secure in the random oracle model. In this paper, we formalize the Chosen-Ciphertext Attack (CCA) security for APOPKE, then we design a scheme called CHAPO (for CHosen-ciphetext attack resistant A Posteriori Openable encryption), and we prove its CCA security in the standard model. CHAPO is approximately twice as efficient as GAPO and is more generic. We also give news applications, and discuss the practical impact of its CCA security.

Domaines: Cryptographie et sécurité [cs.CR]

Xavier Bultel. CCA Secure A Posteriori Openable Encryption in the Standard Model. The Cryptographer’s Track at the RSA Conference (TC-RSA 2022), Mar 2022, San Francisco, United States. ⟨10.1007/978-3-030-95312-6_16⟩. ⟨hal-03754615⟩