TATA CONSULTANCY SERVICES LTD. TATA CONSULTANCY SERVICES LTD. TATA CONSULTANCY SERVICES LTD. TATA CONSULTANCY SERVICES LTD. TATA CONSULTANCY SERVICES LTD. This draft presents a work-in-progress on a challenge-response based lightweight authentication scheme to mutually authenticate CoAP client and server for establishing a secure unicast communication channel. The draft discusses the generic idea behind the proposed authentication scheme, as well as presents its CoAP specific adoption. The proposed scheme has low communication overhead and can be a robust alternative against the usual DTLS based connection initiation scheme with PSK.