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This paper shows that nonperfect secret sharing schemes (NSS) have matroid structures and presents a direct link between the secret sharing matroids and entropy for both perfect and nonperfect schemes. We deene natural classes of NSS and derive a lower bound of jVij for those classes. \Ideal" nonperfect schemes are deened based on this lower bound. We prove(More)
In the model of perfectly secure message transmission schemes (PSMTs), there are n channels between a sender and a receiver. An infinitely powerful adversary A may corrupt (observe and forge) the messages sent through t out of n channels. The sender wishes to send a secret s to the receiver perfectly privately and perfectly reliably without sharing any key(More)
We present and analyze an adaptive chosen ciphertext secure (IND-CCA) identity-based encryption scheme (IBE) based on the well studied Decisional Diffie-Hellman (DDH) assumption. The scheme is provably secure in the standard model assuming the adversary can corrupt up to a maximum of k users adaptively. This is contrary to the Boneh-Franklin scheme which(More)
We rst show that a Feistel type block cipher is broken if the round function is approximated by a low degree vectorial Boolean function. The proposed attack is a generalization of the higher order diierential attack to a probabilistic one. We next introduce a notion of higher order bent functions in order to prevent our attack. We then show their explicit(More)