In Russia, from what I know, there are visa requirements, @Justin267. Maybe a copy is the easiest. If you don't feel comfortable, provide the host with the passport number, valid through date and all the details. And also check online what exactly IS required in Russia.
In my country (Russia's neighbour) it is illegal to copy a document (theoretically), but even if you wat to set up a bank online you'll have to copy your ID and send them.
// "The only person you can trust is yourself"