In "Adaptive Quantum Optics”, adaptive optical methods counteract or even exploit disorder. We have used that to show that with wavefront modulators, multiple-scattering materials can be turned into programmable linear optical networks. The simplest example of a 2x2 network, i.e., a beam splitter, already yields surprising results. In such a network we demonstrate programmable Hong-Ou-Mandel-type two-photon quantum interference. These multiple-scattering materials can also be used as physical authentication keys in quantum protocols. More recently we have studied the transmission of few-photon light pulses through multimode fibers opening up perspectives for authenticated communication.