Masking inquiry

[Stoufs]

If i have a specific file extension i dont want to be read or seen how would i format that as a mask? so in that directory im sharing and any sub folders in it and in that, etc can't see that specific file extension *.ext

[rejetto]

"**/*.ext":
  can_read: false

that should be it, but test it.
i'm trying to have a guide here.
can_read is the internal name for "can download".
this should be enough, as other permissions, like can_see, by default copy from can_read.