Bug 542547

Description of problem:
All of /usr/bin/*sum utilities produce very similar output consisting of a long number of hex-digits, so that later one can't instantly understand what type of hash it is.
It was acceptable in the old md5sum-only days, but now it causes much confusion. For example, see bug #515715.
Of course, one can count the number of digits, but a) that's weird; b) different algorythms can use equal hash length.

The problem would be eliminated if *sum utils could prefix hashes with "type-tag", similarly to what is done in /etc/shadow.  For example, "sha1:..." or "sha1/...".
(And that is THE RIGHT THING -- data of unknown type is bad, so http introduced "Content-type:" header, PGP includes "Hash:" prefix, etc.  With current diversity of hash types, that becomes the barest necessity for *sum utils too...)

Of course, for compatibility reasons, that have to be switched on explicitly -- e.g., with "-l" (Label). And besides adding such tags, *sum have to understand such prefixes, but that's trivial.


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