Lightweight cryptographic systems for services delivered by the recently developed Internet of Things (IoT) are being continuously researched. However, existing Public Key Infrastructure (PKI)-based cryptographic algorithms are difficult to apply to IoT services delivered using lightweight devices. Therefore, encryption, authentication, and signature systems based on Certificateless Public Key Cryptography (CL-PKC), which are lightweight because they do not use the certificates of existing

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... ased cryptographic algorithms, are being studied. Of the various public key cryptosystems, signcryption is efficient, and ensures integrity and confidentiality. Recently, CL-based signcryption (CL-SC) schemes have been intensively studied, and a multi-receiver signcryption (MRSC) protocol for environments with multiple receivers, i.e., not involving endto-end communication, has been proposed. However, when using signcryption, confidentiality and integrity may be violated by public key replacement attacks. In this paper, we develop an efficient CL-based MRSC (CL-MRSC) scheme using CL-PKC for IoT environments. Existing signcryption schemes do not offer public verifiability, which is required if digital signatures are used, because only the receiver can verify the validity of the message; sender authenticity is not guaranteed by a third party. Therefore, we propose a CL-MRSC scheme in which communication participants (such as the gateways through which messages are transmitted) can efficiently and publicly verify the validity of encrypted messages.