  Incorporating rate splitting multiple access (RSMA) into integrated sensing
and communication (ISAC) presents a significant security challenge,
particularly in scenarios where the location of a potential eavesdropper (Eve)
is unidentified. Splitting users' messages into common and private streams
exposes them to eavesdropping, with the common stream dedicated for sensing and
accessible to multiple users. In response to this challenge, this paper
proposes a novel approach that leverages active reconfigurable intelligent
surface (RIS) aided beamforming and artificial noise (AN) to enhance the
security of RSMA-enabled ISAC. Specifically, we first derive the ergodic
private secrecy rate (EPSR) based on mathematical approximation of the average
Eve channel gain. An optimization problem is then formulated to maximize the
minimum EPSR, while satisfying the minimum required thresholds on ergodic
common secrecy rate, radar sensing and RIS power budget. To address this
non-convex problem, a novel optimization strategy is developed, whereby we
alternatively optimize the transmit beamforming matrix for the common and
private streams, rate splitting, AN, RIS reflection coefficient matrix, and
radar receive beamformer. Successive convex approximation (SCA) and
Majorization-Minimization (MM) are employed to convexify the beamforming and
RIS sub-problems. Simulations are conducted to showcase the effectiveness of
the proposed framework against established benchmarks.
