Tar already has the first two, and even POSIX xattrs (which this doesn't preserve), the third seems useless (seems being the key word here, some people might find it useful), and I'd rather just use a program that will encrypt the archive for me (i.e. have a .tar.xz.enc).
One advantage this could have over the above, is if you can open any file at random, as with the above scheme, you might have to linearly decrypt and decompress the entire archive up to that file.
Technically speaking then, the tar utility cannot compress or encrypt per-file, but the tar format can be used for this, and since we're talking about format then the tar format can accomodate the requirements. It's just that there's no tool doing it at the moment.
(A counter point: while each file could be compress and encrypted, there's nothing in the tar format that explicitly says so, meaning that each file would have to be probed to determine if it was compressed or encrypted)
> One advantage this could have over the above, is if you can open any file at random, as with the above scheme, you might have to linearly decrypt and decompress the entire archive up to that file.
4Q uses CBC and the crypto lib doesn't seem to support random access, unless you manually divide your file into separately encrypted streams.
One advantage this could have over the above, is if you can open any file at random, as with the above scheme, you might have to linearly decrypt and decompress the entire archive up to that file.