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A Group Key Agreement Scheme Revisited

In PKC'2004, a constant-round group key exchange protocol is proposed. It takes advantage of the properties of the ElGamal encryption scheme combined with the standard secret sharing technique. In this paper, we show that the scheme can be greatly simplified because the standard secret sharing technique does not work well. Based on the observation, we present a revisited scheme. It saves about 4/5 cost of the original scheme. In addition, its security can be directly reduced to the underlying Schnorr's signature scheme and the ElGamal encryption.