Implementation and Evaluation of an Identity-Based Encryption with Security Against the KGC

Abstract

In identity-based encryption (IBE), a key generation center (KGC) issues a secret key for an identity. Although any value can be used as a public key, the KGC has the potential to decrypt all ciphertexts even if it is not the actual destination. To solve this key escrow problem, Emura, Katsumata, and Watanabe (EKW) proposed an IBE scheme with security against KGC (ESORICS 2019) and provided a pairing-based construction by extending the Boneh-Franklin IBE scheme (CRYPTO 2001). Briefly, they used the Chow framework (PKC 2009), which introduced a new type of authority known as an identity-certifying authority (ICA). Each user obtains an identity certificate from the ICA and can anonymously obtain a secret key from the KGC through an interactive protocol. Though the KGC can issue a secret key without knowing the user’s identity, an additional communication (between the user and the ICA) and computation by the KGC are required compared to the conventional IBE scheme. In this paper, we implement the pairing-based EKW IBE scheme and show that the additional costs are insignificant compared to the Boneh-Franklin IBE scheme.