The　Key-exchange　protocol　is　one　of　the　most　basic　and　widely　used　cryptographic　protocols　in　internet　for　secure　communication.　In　a　two-party　setting,　cryptographic　protocol　design　has　often　ignored　the　possibility　of　simultaneous　message　transmission　by　each　of　the　two　parties.　Most　protocols　for　two-party　have　been　designed　assuming　that　parties　alternate　sending　their　messages.　We　present　two　provably-secure　protocols　for　two-party　authenticated　key　exchange　(AKE)　which　require　not　only　a　single　round,　but　more　efficient　message　transmission　(from　a　computational　perspective).　The　protocol　provides　Implicit　Authentication,　key　independence　and　forward　secrecy,　and　is　analyzed　in　the　standard　model.　The　protocols　are　the　first　provably-secure　one-round　protocol　for　authenticated　2-party　key　exchange　in　the　standard　model　that　the　message　lengths　are　equal　to　the　basic　protocol.　©　2009　Springer　Berlin　Heidelberg.