Provable Secure Identity Based Signcryption Schemes without Random Oracles
Signcryption is a cryptographic primitive which performs encryption and signature in a single logical step with the cost lower than signature-then-encryption approach. Recently, Li et al. proposed the first provable secure identity based signcryption without random oracles. In their scheme sender signs the ciphertext. However, the Boyen showed that non-repudiation is easily achieved if the sender sign the plaintext rather than ciphertext. In this paper, the authors proposed an identity based signcryption scheme without random oracles, which provides the non-repudiation with respect to plaintext. They also proposed an identity based public verifiable signcryption scheme with third party verification in the standard model.