Security of modified Ping-Pong protocol in noisy and lossy channel
  The "Ping-Pong" (PP) protocol is a two-way quantum key protocol based on entanglement. In this protocol, Bob prepares one maximally entangled pair of qubits, and sends one qubit to Alice. Then, Alice performs some necessary operations on this qubit and sends it back to Bob. Although this protocol was proposed in 2002, its security in the noisy and lossy channel has not been proven. In this report, we add a simple and experimentally feasible modification to the original PP protocol, and prove the security of this modified PP protocol against collective attacks when the noisy and lossy channel is taken into account. Simulation results show that our protocol is practical. 
Yun-Guang Han, Zhen-Qiang Yin, Hong-Wei Li, Wei Chen, Shuang Wang,   Guang-Can Guo, Zheng-Fu Han
quant-ph