Efficient signcryption in the standard model

Signcryption is a cryptographic primitive that fulfills both the functions of digital signature and public key encryption simultaneously, at a cost significantly lower than that required by the traditional signature-then- encryption approach. The performance advantage of signcryption over the signature-then-encryption method makes signcryption useful in many applications, such as electronic commerce, mobile communications, and smart cards. In this paper, we propose an efficient signcryption scheme in the standard model. We prove that our scheme satisfies the confidentiality and strong unforgeability. Compared with the Tan's scheme, our scheme has | G | + | p | (320) bits shorter ciphertext, 2 | p | - | G | (160) bits shorter private key, and | G_T | + | G | (1184) bits shorter public key. In addition, in the Tan's scheme, a user must hold two public key/private key pairs at one time if it were both sender and receiver. Our scheme only needs a public key/private key pair, which is more practical for application.