Research On Identity Based Cryptography And Its Application In The Instant Messaging

In identity based cryptograph (IBC), any string, such as an user name, an E-mail address, etc., can be used as an user’s public key, which solves the problem of the complexity and high cost in managing the public key certificates by the public key infrastructure (PKI) in traditional public key cryptograph. However, there are also some security problems in the traditional IBC when solving the problems of managing the public key certificates, such as key exposure and a single point of failure, since the master key of the system is mastered by a single private key generator (PKG).Aiming at the above problems, we propose an IBE scheme and an IBS scheme using the secret sharing technology on the basis of the research in identity based encryption (IBE) and identity based signature(IBS), both of which are based on the secret sharing among multiple PKGs. The core idea is separating the system master key into n secret shares and distributing them to n coordinated PKGs.When applying for the private key, a user sends applications to any t PKGs, and the t PKGs calculate the private key corresponding to the user’s identity using the secret sharing of the master key it mastered after receiving user’s request. Finally the user calculates his own private key according to all the private key fragments he receives. It solves the problem of key exposure and single point of failure in the traditional scheme. Then we present the concrete construction of the scheme, and conduct a rigorous security proof of the proposed scheme.According to the IBE scheme and the IBS scheme based on secret sharing designed, we apply them to the Instant Messaging(IM). Firstly, we design an IM system model based on IBC, which meets the security requirement for confidentiality, integrity and non-repudiation of the user. Then we use Run Time Infrastructure(RTI) as the simulation environment of the communication between entities in IM system to realize the IM System consisting of three kinds of entities:PKG server, IM server and the client. Finally we perform the system test. It turns out that the system realizes the secure communication between users and ensures the confidentiality, integrity and non-repudiation of user’s information.