Signcryption from randomness recoverable public key encryption

We propose a new generic construction for signcryption and show that it is secure under the security models which are comparable to the security against adaptive chosen ciphertext attacks for public key encryption and the existential unforgeability against chosen message attacks for signature. In particular, the security models also capture the notion of insider security. The generic construction relies on the existence of a special class of efficient public key encryption schemes which allow the encryption randomness to be recovered during decryption. We also propose two efficient instantiations for the generic construction and show that one of them has less message expansion and yields smaller ciphertext when compared with all the existing signcryption schemes.