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A Novel Cryptographic Key Assignment Scheme with ID-Based Access Control in a Hierachy

Huang H-F., Chang C-C.

Fundamenta Informaticae

2008

Vol. 84, nr 3-4

353-361

The hierarchical cryptographic key assignment is used to assign cryptographic keys to a set of partially ordered classes so that the user in a higher class can derive the cryptographic key for users in a lower class. However, the existing secure schemes for the cryptographic key assignment in a hierarchy do not consider the situation where a user may be employed for only a period of time. If a user resigned from his position and he premeditatedly eavesdrops on data transmissions, then he can also decrypt some data to obtain useful messages. Thus, all messages are likely to be compromised throughout the system. In this paper, we propose a new cryptographic key assignment scheme in which the cryptographic keys are generated from the identity number of users. Our aim is to minimize the potential damage over a public network. Therefore, as a user who has resigned from his class premeditatedly eavesdrops on later messages, he cannot decrypt the message with his old keys. Moreover, in the proposed method, the key generation and key derivation are quite simple, and the number of the public/secret parameters for each authenticated user is fixed which differs from most previously proposed schemes.

An Efficient and Practical (t, n) Threshold Proxy Signature Scheme with Known Signers

Huang H-F., Chang C-C.

Fundamenta Informaticae

2003

Vol. 56, nr 3

243-253

Previously, all of the proposed threshold proxy signature schemes which have been based on the discrete logarithms required a protocol to generate and verify a shared secret among the proxy group. Therefore, it is necessary for the proxy signers to execute a lot of expensive modular exponential computations and communications to obtain and verify a shared secret. Thus, it is very time-consuming to construct the proxy signature. Moreover, some of the existing threshold proxy signature schemes reveal that the receiver cannot find out who signed the proxy signatures. In this paper, we proposed a practical, efficient, and low communications (t, n) threshold proxy signature scheme based on RSA cryptosystem. By using our way, not only the original signer can know who generated the proxy signature, but also everyone can be a verifier to certify the actuality of the group signers who made it. So, it is very convenient to clarify the responsibility of the document's signers fairly.