Emerging smart grid networks are expected to have massive amounts of data continuously generated from various measuring devices (intelligent sensors, advanced meters, electric vehicle charging stations) which are embedded in the power grid. Data generated from these measuring devices must be delivered securely and reliably to utility control centers for wide-area monitoring and control and to estimate the overall grid status in a timely and precise manner. The collected data is also used for incentivizing consumer participation for improving power stability. Transport protocol requirements for such periodic grid measurement data are characterized as lifetime-lived, secure, and reliable delivery of short flows (usually less than 1.5 KB) over utility-Wide Area Networks (WANs). However, our survey shows that there is no well-known transport protocol that can support the above characteristics in a scalable and light-weight manner. Motivated by this, we design a scalable and secure transport protocol, SSTP, exploiting the notion of a “State-token” which is issued with each server message and which is subsequently attached to corresponding client message delivered to the server. Compared with existing well-known transport and security schemes, SSTP enables scalable server deployments as servers do not keep state (for security and communication) per client and thus computation/memory overheads are significantly reduced.