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Re: [Libreboot] Git clone authentication

From: koanhead
Subject: Re: [Libreboot] Git clone authentication
Date: Sun, 21 Aug 2016 16:53:04 -0700

On 08/20/2016 02:11 AM, Leah Rowe wrote:
> Hi,
> Op 20/08/16 om 01:41 schreef koanhead:
>> Other than that, if you clone the repository in a manner vulnerable
>> to MITM, you should still be able to verify its checksum against
>> the one that's published. As far as I can tell from perusing 
>>, there's no global
>> sum published for the whole tree. This might not matter, since
>> after all we're using git, which uses hashes to identify the
>> objects it tracks. The cgit link above shows some of these hashes.
>> I'm not sure just now how exactly to convince git to emit enough of
>> the correct information that you can compare the results with those
>> shown on the savannah site, so I'm going to send this off as-is and
>> look into it; if I figure it out I'll post in reply to this.
>> Hopefully someone else out there already knows how to do this
>> thing?
> sha1 was broken afaik, I don't remember the link but I was reading
> about it. Whether it's practical in practise to mitm accesses to the
> git repository I don't know. 

As to whether that's practical, I don't know either, but Leah is
definitely right about sha1 having been 'broken' in the sense that it's
possible to generate sha1 hash collisions in somewhat reasonable time.

According to it was
do-able but very expensive in 2005; I expect it's a lot cheaper now.

I had thought that it might be practical to verify the path from the
root of the git tree to the HEAD of whichever branch you're pulling by
validating each hash in order; but that's only a linear increase in
complexity (unless you have lots of branches having lots of branches) so
it doesn't seem like it would be worthwhile to try. If anyone still
wants to try it they can grep the list of commits from `git log`.

Fortunately it doesn't matter, because https!

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