Re: Transparently encrypt repository contents with GPG

From: Michael J Gruber <git@drmicha.warpmail.net>
Date: Mar 14, 2009, 11:16 UTC
Message-ID: <49BB920A.20301@drmicha.warpmail.net>
In-Reply-To: <7vy6v9f9zn.fsf@gitster.siamese.dyndns.org>

Junio C Hamano venit, vidit, dixit 13.03.2009 21:23:

Show 53 quoted lines

> Michael J Gruber <michaeljgruber+gmane@fastmail.fm> writes:
> 
>> In .gitattributes (or.git/info/a..) use
>>
>> * filter=gpg diff=gpg
>>
>> In your config:
>>
>> [filter "gpg"]
>>         smudge = gpg -d -q --batch --no-tty
>>         clean = gpg -ea -q --batch --no-tty -r C920A124
>> [diff "gpg"]
>>         textconv = decrypt
>>
>> This gives you textual diffs even in log! You want use gpg-agent here.
> 
> Don't do this.
> 
> Think why the smudge/clean pair exists.
> 
> The version controlled data, the contents, may not be suitable for
> consumption in the work tree in its verbatim form.  For example, a cross
> platform project would want to consistently use LF line termination inside
> a repository, but on a platform whose tools expect CRLF line endings, the
> contents cannot be used verbatim.  We "smudge" the contents running
> unix2dos when checking things out on such platforms, and "clean" the
> platform specific CRLF line endings by running dos2unix when checking
> things in.  By doing so, you can see what really got changed between
> versions without getting distracted, and more importantly, "you" in this
> sentence is not limited to the human end users alone.
> 
> git internally runs diff and xdelta to see what was changed, so that:
> 
>  * it can reduce storage requirement when it runs pack-objects;
> 
>  * it can check what path in the preimage was similar to what other path
>    in the postimage, to deduce a rename;
> 
>  * it can check what blocks of lines in the postimage came from what other
>    blocks of lines in the preimage, to pass blames across file boundaries.
> 
> If your "clean" encrypts and "smudge" decrypts, it means you are refusing
> all the benifit git offers.  You are making a pair of similar "smudged"
> contents totally dissimilar in their "clean" counterparts.  That is simply
> backwards.
> 
> As the sole raison d'etre of diff.textconv is to allow potentially lossy
> conversion (e.g. msword-to-text) applied to the preimage and postimage
> pair of contents (that are supposed to be "clean") before giving a textual
> diff to human consumption, the above config may appear to work, but if you
> really want an encrypted repository, you should be using an encrypting
> filesystem.  That would give an added benefit that the work tree
> associated with your repository would also be encrypted.

Exactly. This is why I suggested using cryptfs/luks in my first response already.

But I don't know the OP's requirements, which is why I also told him how to do what he wanted, even though it has the drawbacks you and Jeff (and maybe I) mentioned. Maybe it's an attempt at hosting a semi-private repo on a public (free) server?

Besides the non-text nature of encrypted content, the problem here is that d(e(x))=x for all x but e(d(x)) differs from x most probably, and hopefully randomly, unless you use the right version of debian's openssl of course ;)

That being said: git diff calls textconv filters with smudged as well as cleaned files (when diffing work tree files to blobs), and this does not seem right. I hope this is not happening with the internal diff, nor with crlf!

Since both the cleaned and the smudged version are supposed to be "authoritative" (as opposed to the textconv'ed one) one may argue either way what's the right approach. For internal use comparing the cleaned versions may make more sense, for displaying diff's the checked-out form, i.e. smudged versions make more sense.

But that is another topic which would need to be substantiated with tests. It's not completely unlikely I may come up with some, but don't count on it...

Cheers, Michael