Re: Migrating away from SHA-1?

[Joey Hess <id@joeyh.name>]

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Theodore Ts'o wrote:
> OK, so how does this map to git?  First of all, from a collision
> perspective, the two blobs have to map into valid C code

Git provides other places to hide the colliding blobs; the best seems to
be as an added header in the commit object, or as trailing data after a \0
in the commit message. git is very good at hiding such potentially
colliding data from the user, as https://github.com/joeyh/supercollider
demonstrates.

commit 24f30db5790b209fa412ce81c5ef2bf8af5fd4d7
Author: Joey Hess <joey@kitenet.net>
Date:   Fri Sep 9 11:49:21 2011 -0400

    an innocent commit
    
    If this were a sha1 colliding attack, there would be some sort of binary
    garbage below. Which there isn't. So this can be safely merged.

joey@darkstar:~/tmp/supercollider>git cat-file -p 24f30db5790b209fa412ce81c5ef2bf8af5fd4d7
tree 735a7633237c07b398856005de3bc9ea00446747
author Joey Hess <joey@kitenet.net> 1315583361 -0400
committer Joey Hess <joey@kitenet.net> 1315583361 -0400

an innocent commit

If this were a sha1 colliding attack, there would be some sort of binary
garbage below. Which there isn't. So this can be safely merged.
\0


??b???\x1f[?i??ͯ?t?\f2??\x02????os?\x14<????h?+,M?mY?e?EW?i\x13v$???\x14J??U}n~???L??????f??\x02?ě??3>?Q??H?޸\x16*zl\x1a?RA˂q?E\f?\x06\x16E\x7f7??^[?\x03\?m???U?\x1e>MU\v	GY?d)?ȼ??'g?~D??ɯhQ?\x13???/"E\x04??X?m???^͸??S?D\x13??;w6(?`??>?\x10縘?\aAѲ?*!??@v????>?8??2\b?\x14!??=*?J	^[\r\r???\x01ynH\x10???c?w?\??K7??\x1c?N?6??\x1c???A5?FM?wZ?~?pK\x02Y?R???s7\x7f??(?\aƶ?_"??m\x11%????\x7f1\x7fa??ʀ??K[\rt??\x11??\x0e!A0?ΈfT.?T?w\a?򁛵ƌ\v?р???aco?V/2\x14??nَ?
?}?6?\x19_?z?{


(The other possibility would be to hide the colliding blob in the tree
object, but that seems unlikely.)

-- 
see shy jo

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