I think you need to rigorously define your macrostates. If your two states are "my friend's password" and "not my friend's password" then the macrostates are perfectly objective. You don't know what macrostate the system is in, but that doesn't change the fact that the system is objectively in one of those two macrostates.
If you define your macrostates using subjective terms (e.g. "a string that's meaningful to me" or "a string that looks ordered to me") then yeah, your entropy calculations will be subjective.
If you define your macrostates using subjective terms (e.g. "a string that's meaningful to me" or "a string that looks ordered to me") then yeah, your entropy calculations will be subjective.