  "Device-independent" not only represents a relaxation of the security
assumptions about the internal working of the quantum devices, but also can
enhance the security of the quantum communication. In the paper, we put forward
the first device-independent quantum secure direct communication (DI-QSDC)
protocol, where no assumptions are made about the way the devices work or on
what quantum system they operate. We show that in the absence of noise, the
DI-QSDC protocol is absolutely secure and there is no limitation for the
communication distance. However, under practical noisy quantum channel
condition, the photon transmission loss and photon state decoherence would
reduce the communication quality and threaten its absolute security. For
solving the photon transmission loss and decoherence problems, we adopt
noiseless linear amplification (NLA) protocol and entanglement purification
protocol (EPP) to modify the DI-QSDC protocol. With the help of the NLA and
EPP, we can guarantee the absolute security of the DI-QSDC and effectively
improve its communication quality.
