A public key cryptosystem and a signature scheme based on discrete logarithms
Proceedings of CRYPTO 84 on Advances in cryptology
A method for obtaining digital signatures and public-key cryptosystems
Communications of the ACM
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Proceedings of the 3rd ACM conference on Electronic Commerce
A Practical Public Key Cryptosystem Provably Secure Against Adaptive Chosen Ciphertext Attack
CRYPTO '98 Proceedings of the 18th Annual International Cryptology Conference on Advances in Cryptology
A Quick Group Key Distribution Scheme with "Entity Revocation"
ASIACRYPT '99 Proceedings of the International Conference on the Theory and Applications of Cryptology and Information Security: Advances in Cryptology
On Quorum Controlled Asymmetric Proxy Re-encryption
PKC '99 Proceedings of the Second International Workshop on Practice and Theory in Public Key Cryptography
Time-lock Puzzles and Timed-release Crypto
Time-lock Puzzles and Timed-release Crypto
Conditional oblivious transfer and timed-release encryption
EUROCRYPT'99 Proceedings of the 17th international conference on Theory and application of cryptographic techniques
Design of a secure digital contents delivery system in p2p networks
DRMTICS'05 Proceedings of the First international conference on Digital Rights Management: technologies, Issues, Challenges and Systems
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A cryptographic approach that enables a peer to transfer the right to access the encrypted data provided predetermined conditions are satisfied is presented in this paper. Our approach involves a third trusted service, called "delegation check (DC) servers" to check single or multiple conditions according to the rules. A peer (delegator) delegates the right to decrypt the ciphertext to other peers (proxies) under certain conditions. The proxy can decrypt the ciphertext only after it passes the verification check of the DC server. Our system has the following properties: (1) A sender does not need to know whether or not the delegation occurs. (2) DC servers are involved only when the proxy decrypts the ciphertext. (3) Neither the DC server nor a proxy can know the private decryption key of the delegator unless both of them collude with each other.Two types of techniques, a basic scheme and an extended scheme, are presented. The basic scheme is relatively efficient, while the security is maintained under the assumption that the DC server does not deviate from the protocol. In order to tolerate the deviation of the DC server, the extended scheme allows the delegator to direct the proxy to use a group of servers when decrypting the ciphertext. A notable feature in our scheme is that the delegator can independently choose which of the two without any interaction with the DC servers or the proxy. Moreover, the choice of the scheme does not require any modification of the operations that the server performs.