[Rpm-ecosystem] Some points about zchunk

[Jonathan Dieter]

On Sun, 2018-07-08 at 19:45 +0100, Jonathan Dieter wrote:
> On Fri, 2018-07-06 at 11:48 +0000, Michael Schroeder wrote:
> > Ah, no, I think you misunderstood. Do *not* add md5 support. In fact,
> > I'd ask you to remove sha1 support as well to make your code smaller.
> > 
> > My point is that you shouldn't use 20 bytes just for chunk identification
> > purposes. As you said, it doesn't need to be cryptographically sound, we
> > don't have to make sure it withstands an attacker.
> > Just use the first 8 bytes of the sha256 sum instead (or sha512, as
> > it's a bit faster than sha256 IIRC).
> 
> Ok, that makes sense.  I'll add it as a new hash type (SHA512_64?) and
> make it the default for the chunk checksum.

Ok, I've added two new hash types, ZCK_HASH_SHA512 and
ZCK_HASH_SHA512_64.  The latter is the new default for chunk hashes.

https://github.com/zchunk/zchunk/commit/abdfa43ea05b1b3d6dbd3b330572abe
eb0d8444f

I think I'll leave the SHA1 support in, at least for a while, since
it's been the default chunk hash up until now, and I'd hate to break
any zchunk files that people might have created.

Jonathan