Hello again!
First of all, I'd like to thank all of You for your answers. They where helpful and helped me to clarify some things. I guess it's true that I should learn a bit more about "Alice & Bob" before asking questions. I think I'll use IPsec or Kerberos like Daniel suggested, but of course firstly I'll read more about this. Anyway - Daniel I'll remember what you said about "openWRT" and "help" ;-)
However, I'm still concerned about issue of using fake nodes claiming they are someone else (e.g. sending fake OGMs) for sole reason of destroying the mesh. Do you think this is important issue? Can it be somehow reduced?