Re: [PATCH v2 2/2] doc hash-function-transition: pick SHA-256 as NewHash

From: brian m. carlson <sandals@crustytoothpaste.net>
Date: Aug 3, 2018, 17:45 UTC
Message-ID: <20180803174558.GC106068@genre.crustytoothpaste.net>
In-Reply-To: <20180803072014.GA256410@aiede.svl.corp.google.com>

On Fri, Aug 03, 2018 at 12:20:14AM -0700, Jonathan Nieder wrote:

Show 26 quoted lines

> Ævar Arnfjörð Bjarmason wrote:
> >  Object format
> >  ~~~~~~~~~~~~~
> >  The content as a byte sequence of a tag, commit, or tree object named
> > -by sha1 and newhash differ because an object named by newhash-name refers to
> > +by sha1 and sha256 differ because an object named by sha256-name refers to
> 
> Not about this patch: this should say SHA-1 and SHA-256, I think.
> Leaving it as is in this patch as you did is the right thing.
> 
> [...]
> > @@ -255,10 +252,10 @@ network byte order):
> >    up to and not including the table of CRC32 values.
> >  - Zero or more NUL bytes.
> >  - The trailer consists of the following:
> > -  - A copy of the 20-byte NewHash checksum at the end of the
> > +  - A copy of the 20-byte SHA-256 checksum at the end of the
> 
> Not about this patch: a SHA-256 is 32 bytes.  Leaving that for a
> separate patch as you did is the right thing, though.
> 
> [...]
> > -  - 20-byte NewHash checksum of all of the above.
> > +  - 20-byte SHA-256 checksum of all of the above.
> 
> Likewise.

For the record, my code for these does use 32 bytes. I'm fine with this being a separate patch, though.

Show 13 quoted lines

> [...]
> > @@ -351,12 +348,12 @@ the following steps:
> >     (This list only contains objects reachable from the "wants". If the
> >     pack from the server contained additional extraneous objects, then
> >     they will be discarded.)
> > -3. convert to newhash: open a new (newhash) packfile. Read the topologically
> > +3. convert to sha256: open a new (sha256) packfile. Read the topologically
> 
> Not about this patch: this one's more murky, since it's talking about
> the object names instead of the hash function.  I guess "sha256"
> instead of "SHA-256" for this could be right, but I worry it's going
> to take time for me to figure out the exact distinction.  That seems
> like a reason to just call it SHA-256 (but in a separate patch).

My assumption has been that when we are referring to the algorithm, we'll use SHA-1 and SHA-256, and when we're referring to the input to Git (in config files or in ^{sha256} notation), we use "sha1" and "sha256". I see this as analogous to "Git" and "git".

Otherwise, I'm fine with this document as it is.

-- 
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204