  We demonstrate high-rate randomized data-encryption through optical fibers
using the inherent quantum-measurement noise of coherent states of light.
Specifically, we demonstrate 650Mbps data encryption through a 10Gbps
data-bearing, in-line amplified 200km-long line. In our protocol, legitimate
users (who share a short secret-key) communicate using an M-ry signal set while
an attacker (who does not share the secret key) is forced to contend with the
fundamental and irreducible quantum-measurement noise of coherent states.
Implementations of our protocol using both polarization-encoded signal sets as
well as polarization-insensitive phase-keyed signal sets are experimentally and
theoretically evaluated. Different from the performance criteria for the
cryptographic objective of key generation (quantum key-generation), one
possible set of performance criteria for the cryptographic objective of data
encryption is established and carefully considered.
