Efficient proxy signcryption scheme with provable CCA and CMA security

For facilitating the confidential transaction with delegation such as on-line proxy auction and business contract signing by an authorized proxy, we propose an efficient proxy signcryption scheme from pairings. Our scheme allows an original signer to delegate his signing power to a proxy one such that the latter can signcrypt a plaintext on behalf of the former. The signcrypted message can only be decrypted by a designated recipient who is also responsible for verifying the recovered proxy signature. To deal with a later dispute over repudiation, the designated recipient can easily announce the ordinary proxy signature for public verification without extra computational efforts. To guarantee the realistic applicability, we demonstrate that our scheme outperforms previous works in terms of functionalities and computational efficiency. Moreover, the security requirement of confidentiality against indistinguishability under adaptive chosen-ciphertext attacks (IND-CCA2) and that of unforgeability against existential forgery under adaptive chosen-message attacks (EF-CMA) are proved in random oracle models.