Thanks ! I finally successed to use signing but it was quite difficult because I speak just a little bit english and The only step by step guide that I've found is for mySensor V1.5 and not for 2.0.
My difficulty comes that I didn't understand that I had to flash EEPROM with Keys(with SecurityPersonnalizer.ino) and then flash my sketch. Finally, I added in Gateway and Sketches these lines
#define MY_SIGNING_SOFT_RANDOMSEED_PIN 7
And now it works !!
I've just noticed some communication errors sometimes... Perhaps it's because signing protocole needs more messages exchanges
between nodes and gateway.