Research On Revocable Key And Convertible Ciphertext Cryptography Algorithms

In traditional public key cryptography if a user’s private key is compromised, it can be solved by revoking the user’s public key. However, user’s public key is the unique identity information in identity-based cryptography, so the slight modification or revocation about public key will causes the change of user’s identity information. Therefore, how to effectively implement mechanism of revocation is becoming a critical problem in identity-based cryptography.Proxy re-encryption allows a semi-trusted proxy to translate a ciphertext encrypted under one public key into another ciphertext under another public key on the same plaintext. This translation requires the proxy can not get any information about the plaintext. Therefore, proxy re-encryption completes the purposes of data sharing and forwarding on the premise of guaranteeing data confidentiality. It is of great significance for information storage to design a secure and efficient proxy re-encryption scheme.In view of the above problems that to be solved, the main points of this paper are as follows:1. A new revocable identity-based signcryption scheme was proposed. In the new scheme, the master key was randomly divided into two parts: one was used to construct the initial key, the other was used to generate updated key. Furthermore, they were used to generate(designcryption) signcryption key randomly, thus the proposed scheme can revoke users and resist key compromise attack. In the standard model, we prove the new scheme with IND-CCA2 security under the hardness of DBDH problem and EUF-CMA security under the hardness of CDH problem.2. A new multi-use ciphertext-policy unidirectional proxy re-encryption scheme was proposed, that can realizes the multiple times transformation of ciphertext under fine-grained access control. In the proposed scheme, the tree access policy can be used to handle ‘and’( ?),‘or’( ?)and ‘threshold’( of) attribute control, and our scheme satisfies the property of re-encryption control. Moreover, we show that the proposed scheme based on the ADBDH difficult assumption with IND-SAP-CCA security in the standard model.