  Leakage of information in power line communication networks is a threat to
privacy and security both in smart grids and in-home applications. A way to
enhance security is to encode the transmitted information with a secret key.
Relying on the channel properties, it is possible to generate a common key at
the two communication ends without transmitting it through the broadcast
channel. Since the key is generated locally, it is intrinsically secure from a
possible eavesdropper. Most of the existing physical layer key generation
techniques have been developed for symmetric channels. However, the power line
channel is in general not symmetric, but just reciprocal. Therefore, in this
paper, we propose two novel methods that exploit the reciprocity of the power
line channel to generate common information at the two intended users. This
information is processed through different quantization techniques to generate
secret keys. To assess the security of the generated keys, we analyze the
spatial correlation of the power line channels and verify the low correlation
of the possible eavesdropping channels. The two proposed methods are tested on
a measurement dataset. The results show that the information leaked to possible
eavesdroppers has very low correlation to any secret key.
