The present invention provides a method for keys generation, member authentication and communication security in a dynamic group, which comprises steps: assigning each member an identification vector containing common group identification vector elements and an individual identification vector element, and generating an authentication vector and an access control vector for each member according to the identification vector; using the identification vector elements to generate public key elements and establish an authentication public key and an access control public key; and using a polynomial and the identification vector to generate a private key. The present invention uses these public keys and private keys, which are generated from the identification vectors, to implement serverless member authentication and data access control, whereby is protected privacy of members and promoted security of communication.