Abstract: According to the characteristics of limited number of domain agents and to solve the complex computational problems in the current crossdomain authentication process based on identity, an algorithm based on trust for users to crossdomain access information services entity (ISE) resources is proposed. The algorithm adopts a combination of trust and identitybased cryptosystems. The algorithm firstly completes the identity authentication of users in the domain agent, and then judges the trust degree by using the proposed trust judgment method to achieve the purpose of bidirectional authentication, and finally realizes user crossdomain access ISE. The simulation results show that the method of judging trust effectively resists attacks from “malicious” domain agents. Compared with identitybased crossdomain authentication, the scheme based on trust for ISE reduces the amount of calculation and communication cost.