> but this doesn't need to be a "drop everything" hurry task.

Totally agree! :)

Thanks for the information with the page on mediawiki.org. I'll take a look and 
probably edit it, if I see something :P

Best,
Florian

-----Ursprüngliche Nachricht-----
Von: Wikitech-l [mailto:[email protected]] Im Auftrag von 
Brion Vibber
Gesendet: Freitag, 24. Februar 2017 19:48
An: Wikimedia developers <[email protected]>
Betreff: Re: [Wikitech-l] SHA-1 hash officially broken

On Fri, Feb 24, 2017 at 10:34 AM, Florian Schmidt < 
[email protected]> wrote:

> I searched in phabricator, if we've a task already, but couldn't find any.
> However, as the phabricator search and me aren't really good friends, 
> it's possible, that the search wasn't as honest to me, as I would wish 
> and I missed something, so I ask on this list :) Do we've a task 
> already to track the work on this topic? A short github search[1] 
> showed some usages of sha1 (at least the string), so I suspect, that 
> there're some places where we use it, right?
>
> [1] 
> https://github.com/wikimedia/mediawiki/search?utf8=%E2%9C%93&q=SHA1


Usages are listed at https://www.mediawiki.org/wiki/Manual:Hashing -- I've 
added a "purpose" column on the DB fields list. There might be a couple we 
missed, so feel free to edit!


It looks like img_sha1 and fa_storage_key are the biggest practical dangers of 
collision, in that pairs of images could be created such that, say, one is a 
cute kitten and the other is a shock image, such that deletion and undeletion 
might surface the wrong file from what the undeleting admin expected.

However since the attack requires creating a common prefix and suffix for the 
matching pair of files, there's little or no danger of an attack that replaces 
legitimate files already uploaded by someone else.

I would probably recommend migrating rev_sha1 and img_sha1's usages in 
collision detection over to a rev_sha256 and img_sha256 columns, and reworking 
filearchve to use a sha-256 hash for content addressing of new files, but this 
doesn't need to be a "drop everything" hurry task.

-- brion
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