On DDos attack against proxy in proxy re-encryption and proxy re-signature

In 1998, Blaze, Bleumer and Strauss proposed new kind of cryptographic primitives called proxy re-encryption and proxy re-signature[3]. In proxy re-encryption, a proxy can transform a ciphertext computed under Alice's public key into one that can be opened under Bob's decryption key. In proxy re-signature, a proxy can transform a signature computed under Alice's secret key into one that can be verified by Bob's public key. Proxy re-cryptography can find many interesting applications in our life. In this paper, we introduce a new attack- DDos attack against proxy in the proxy re-cryptography. Although this attack can also be implemented against other cryptographic primitives, the danger caused by it in proxy re-cryptography seems more serious. We revisit the current literature, paying attention on their resisting DDos attack ability. We suggest a solution to decline the impact of DDos attacking. Also we give two new efficient proxy re-encryption schemes which can achieve CCA2 secure based on Cramer-Shoup encryption scheme and prove its security. At last we give our conclusions with hoping researchers to pay more attention to this attack.