Network simulator is good as far as I know due to it is easy to handle WSN.

you can opt for CASTALIA as  we can integrate C/C++ code for security in that easily.

TETCOS Netsim seems to be what you are looking for.

Z-monitor for wireless sensor networks

Mrewaabd by the Protocols forum

application on the location wireless sensor réseaus

Meradiyounes by the Embedded Forum

UWB for wireless sensor networks

By imane_it in MATLAB forum

Multimedia networks without wire sensors

By angelange in Development forum

you can use omnet++ or matlab

Thank you Thushari for your reply, Could you please send me the link to the the mentioned network simulator as I couldn’t find it. Thanx

Thanks Jitendra, Can I use CASTALIA alone as a separate simulator, or I have to use it with Omnet++.  Many thanx.

Thank you Tandin, I haven't heard about TETCOS Netsim before, but I went through their website, and it seems this software for educational purpose. It support only Symmetric encryption. Please share your experience if you have worked on this simulator. Thanx.

Abdelhakim, I don't understand your answer!!, you may misunderstand my question.

CPN Tools is a tool for

editing, simulating, and analyzing Colored Petri nets.

Thanks Shahab, MATLAB is a nice and huge simulator, but there is some Simulation software designed especially for WSN which make the simulation easier. Omnet++ is what in my mind now since I could integrate it with Castalia. Still waiting opinion who used one of the those suggested Simulators in the area of securing WSNs.

NS2 or NS3 would be good choice because it has been used a lot in the field of sensor networks.

Thanks Rasheed, I came cross some papers about securing WSN, and I noticed they used NS2 as a simulator. I think NS2 not anymore accepted by most publishers. Only NS3 is now acceptable.  

I don't know 100%, but I read NS2 is best for simulation. I studied in wikipedia, in NS3  is not good for all simulation. 

I think that you can try this in Omnet++ and inet Framework 

Thanks Guys your answers is really appreciated. I am still would like to hear from someone who already has used either omnet++ or NS2 for WSN encryption.