Figure2
![Split keys for station-to-station (STS) protocols](https://image.oaes.cc/5f56c4b0-222d-4544-ad97-92284cf5e49b/jsss4016-2.jpg)
Figure 2. Cases of the system model: (ⅰ) no split key; (ⅱ) Alice's keys are split between Alice1-Alice2; (ⅲ) Bob's keys are split between Bob1-Bob2; (ⅳ) both Alice's and Bob's keys are split between Alice1-Alice2 and Bob1-Bob2, respectively.