You will not travel with your private keys! You will travel with a public key of your choice, printed in QR code. In the assembly, you put this printed public key into a physical ballot box. Everyone who attends the assembly do the same. Then the printed public keys are counted and expected to be equal to the number of people that attend the meeting. Everyone leaves the assembly having the list of all public keys. Those keys are considered now as a proof of individuality, that can be used for now on in the internet in order to prove that you are a real person. Many similar assemblies can be organized in several towns, as long as those assemblies are absolutely concurrent, and a web of trust among those assemblies is established. Having this proof of individuality in your hands, you can now claim in the internet your masternode votes, by signing the public keys of the masternodes with the private key of the printed public key you put into the physical ballot box.