This document specifies the details of the Host Identity Protocol Diet EXchange (HIP DEX). HIP DEX is a variant of the HIP Base EXchange (HIP BEX) [RFC5201-bis] specifically designed to use as few crypto primitives as possible yet still deliver the same class of security features as HIP BEX. The design goal of HIP DEX is to be usable by sensor devices that are memory and processor constrained. Like HIP BEX it is expected to be used together with another suitable security protocol, such as the Encapsulated Security Payload (ESP). HIP DEX can also be used directly as a keying mechanism for a MAC layer security protocol as is supported by IEEE 802.15.4 [IEEE.802-15-4.2006].