What?! Dosbox itself cannot be password protected under any circumstances. It is a violation of their GPL. Any archived games with Dosbox as part of the install cannot have a password of any sort blocking access to Dosbox itself. Can anybody confirm that Dosbox games are affected before I shoot off an email to the Dosbox team?
Actually no, the GPL doesn't prevent it at all, at least not GPL v2. (for v3 it's a little more tricky)
You could have somebody take Dosbos source code load it with always online DRMs, include games encryption requiring a one time on-line unlock token to be run, or even streaming part the game content from an online server, and yet it would still be perfectly ok with the GPL as long as the person in question provide the source code of all his modifications.
The GPL doesn't forbid DRMs, encryption, restriction, whatever, it only says that you have to, if requested, provide the source code of the original program and of all the modifications you made to it.