Several 3-party-based authentication protocols have been proposed, which are resistant to off-line password guessing attacks. We show that they are not resistant to a new type of attack called "undetectable on-line password guessing attack". The authentication server is not able to notice this kind of attack from the clients' (attacker's) requests, because they don't include enough information about the clients (or attacker). Either freshness or authenticity of these requests is not guaranteed. Thus the authentication server responses and leaks verifiable information for an attacker to verify his guess.

No abstract

No abstract

There have been many approaches in the past to generalize the ElGamal signature scheme. In this paper WC integrate all these approaches in a Meta-ElGamal signature scheme. We also investigate some new types of variations, that haven't been considered before. By this method we obtain in our example settings numerous variants of the ElGamal scheme. From these variant.s, we can extract new, highly efficient signature schemes, which haven't been proposed before. As an example, we present efficient DSA-variants.

No abstract