We present practical conference key distribution systems based on public keys, which authenticate the users and which are 'proven' secure provided the Diffie-Hellman problem is intractable. A certain number of interactions is needed but the overall cost is low. There is a complexity tradeoff. Depending on the network used, we either have a constant (in the number of conference participants) number of rounds (exchanges) or a constant communication and computation overhead. Our technique for authentication can be extended and used as the basis for an authentication scheme which is (proven' secure against any type of attack, provided the Discrete Logarithm problem is intractable.

Abstract.In a society oriented cryptography it is better to have a public key for the company (organization) than having one for each individual employee [.es88]. Certainly in emergency situations, power is shared in many organizations.Solutions to this problem were presented [.e.s88], based on [GMW87], but are completely impractical and intemctive. In this paper practical non-intemctiue public key systems are proposed which allow the reuse of the shared secret key since the key is not revealed either to insiders or to outsiders.

Abstract. In this paper, we show that a key encapsulation mechanism (KEM) does not have to be IND-CCA secure in the construction of hybrid encryption schemes, as was previously believed. That is, we present a more efficient hybrid encryption scheme than Shoup [12] by using a KEM which is not necessarily IND-CCA secure. Nevertheless, our scheme is secure in the sense of IND-CCA under the DDH assumption in the standard model. This result is further generalized to universal2 projective hash families.

In a society oriented cryptography it is better to have a public key for the company (organization) than having one for each individual employee [.es88]. Certainly in emergency situations, power is shared in many organizations. Solutions to this problem were presented [.e.s88], based on [GMW87], but are completely impractical and intemctive. In this paper practical non-intemctiue public key systems are proposed which allow the reuse of the shared secret key since the key is not revealed either to insiders or to outsiders.