S. Akl and P. Taylor (Proc. Crypto-82, p.237-250, 1982) proposed an elegant solution to the multilevel key distribution problem, using a cryptographic approach. In the present work, two problems associated with the Akl-Taylor scheme are considered. First, a time-memory tradeoff technique to overcome the problem of the extremely large memory space required by the Akl-Taylor scheme is proposed. Second, an extended scheme that localizes within a small region as much as possible the inserting/deleting problem associated with the Akl-Taylor scheme is proposed.>

Proposes two distinct cryptosystems based on Rabin's scheme. The first incorporates coding theory and provides encryption only. The second provides simultaneously both private encryption and digital signature for network users. In the cases where the second scheme provides only encryption or only digital signature, the scheme provides that the bit ratio between plaintext and ciphertext is 1:1, i.e. equivalent to that of the RSA scheme.>

The authors propose a decentralized key distribution scheme. In this scheme, there are as many local key centers as needed and each user needs to select a key center at which to register when first joining the network. The most significant feature of the method is that each center needs only a single secret key. All personal keys that it needs for delivering encrypted keys to groups of users can be derived from this single key through a one-way function.>