I think you can easily make tar-archives that contain a checksum, if
you agree on some extremely mild file naming convention for such a
checksum (i.e., the archive is not allowed to contain a filename that
clashes with the file that stores the checksum). Of course, the key is
that when you add something to the archive, the file changes, so the
plain md5sum of the total archive changes. You have to md5sum
something that is easily extracted and independent of the later added
md5sum. The options -O (dump to stdout), -r (append file) and --
exclude provide the necessary features for tar.
Procedure for storing a checksum in a tar archive:
----------------------------------
(tar xf file.tar --exclude md5sum.check -O; \
tar tvf file.tar --exclude md5sum.check ) | md5sum > md5sum.check
tar -rf file.tar md5sum.check
----------------------------------
Procedure for checking that the stored sum agrees with the computed
one:
----------------------------------
tar xf file.tar md5sum.check -O > storedcheck
(tar xf file.tar --exclude md5sum.check -O; \
tar tvf file.tar --exclude md5sum.check ) | md5sum > computedcheck
cmp storedcheck computedcheck
----------------------------------
Note that we need to include the directory listing information as
well, because the output of -O does not include file names
(i.e., one could move files around and still have the same checksum)
If it is ever decided that .spkgs should be signed, then you could
include a .gpg-file via the same procedure.
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