  In this brief review, we discuss the role that quantum correlations, as
quantified by quantum discord, play in two interesting settings. The first one
is discerning which unitaries have been applied on a quantum system, by taking
advantage of knowledge regarding its initial configuration. Here discord
captures the "quantum" component of this knowledge, useful only when we have
access to a quantum memory. In particular, discord can be used to detect
whether an untrusted party has certain quantum capabilities. The second setting
is quantum cryptography. Here discord represents an important resource for
trusted-noise quantum key distribution and also provides a general upper bound
for the optimal secret key rates that are achievable by ideal protocols. In
particular, the (two-way assisted) secret key capacity of a lossy bosonic
channel exactly coincides with the maximum discord that can be distributed
between the remote parties at the two ends of the channel.
