Isn't this the only part of this that's really important? If you can see me in real life, if I can give you a cryptographically secure way to check whatever I'm sending you in the future, badda bing, mission success. It's only a problem if my code becomes compromised on my end, leaked or something. It requires faith that your friends won't get compromised, but that's pretty much going to be true of any system you might devise there. That's not the job of cryptography, or some document the government has, that's just the job of your own personal security practices to make sure you're not giving around codes and passwords willy nilly. I don't understand why this really needs to be tied to the government or to specific people at all.