Signcryption is a cryptographic primitive that combines both the functions of digital signature and public key encryption in a logical single step, at lower computational costs and communication overheads than the traditional signature-then-encryption approach. This thesis analyzes the present identity-based signcryption scheme, and puts forward a new identity-based signcryption scheme without trust authority by using bilinear pairings. In addition, it also analyzes the safety and efficiency of this scheme. Analysis shows that this proposal meets the safety and high efficiency requirement of Signcryption.