Efficient Method to Construct Identity-Based Signcryption Scheme

MasterEncryption and signature have been considered the fundamental cryptographic tools of public key cryptography for providing private and authenticated communications. An encryption scheme ensures that an adversary cannot learn any information about a plaintext from ciphertexts (i.e., confidentiality) and a signature scheme ensures that an adversary cannot forge a new valid signature on a new plaintext (i.e., non-repudiation). Many applications require these two distinct goals to be simultaneously achieved. By applying two distinct toolsto applications sequentially, both confidentiality and non-repudiation can be achieved easily. However, this process performs unnecessary operations, and thus wastes resources. Encryption and signature can be efficiently combined to provide both confidentiality and non-repudiation simultaneously. Signcryption is a scheme that encrypts and signs data in a single operation which is more efficient than using an encryption scheme combined with a signature scheme.In identity-based cryptography, an arbitrary string can be used as a public key, and a private key is derived from the public key. Therefore, a sender uses identity information (e.g., mail address, name, and phone number) of a receiver as a public key and the receiver can get a corresponding private key from the private key generator (PKG) after receiving a ciphertext from the sender. In the system, users do not need to obtain certificates.Identity-based signcryption (IBSC) applies the idea of identity-based cryptography to signcryption. The first IBSC scheme considered two security notions: confidentiality and non-repudiation. Confidentiality requires indistinguishability against adaptive chosen-ciphertext attacks and non-repudiation requires unforgeability against chosen-message insider attacks. Three other security requirements are needed for IBSC: ciphertext anonymity, ciphertext unlinkability, and ciphertext authentication. Since then, much research has been proceeded on IBSC. Recently, Pandey et al. proposed an efficient construction of IBSC using an IBE scheme and an IBS scheme. However, their scheme only achieves confidentiality and non-repudiation.This thesis shows a method to construct an efficient IBSC scheme by improving the Pandey scheme. The IBSC scheme in this thesis satisfies ciphertext authentication, message confidentiality, signature non-repudiation, and ciphertext anonymity. The security is proved by using the random oracle model. This thesis compare the proposed scheme with other schemes in the literature