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Joey Hess 2017-02-24 02:14:36 -04:00
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doc/todo/sha1_collision_embedding_in_git-annex_keys.mdwn
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@ -27,15 +27,15 @@ A few other potential problems:
Impact is limited, because even if an attacker does this, the key also Impact is limited, because even if an attacker does this, the key also
contains the checksum (eg SHA2) of the annexed data. The current SHA1 contains the checksum (eg SHA2) of the annexed data. The current SHA1
attack is only a prefix attack; it does not allow creating two colliding attack is only a common-prefix attack; it does not allow creating two
keys that contain two different SHA2 checksums. That would need a colliding keys that contain two different SHA2 checksums. That would need a
preimage attack to be feasible. chosen-prefix attack to be feasible.
It might be worth limiting the length It might be worth limiting the length
of an extension allowed in such a key to the longest such extension of an extension allowed in such a key to the longest such extension
git-annex has ever supported (probably < 20 bytes or so), which would git-annex has ever supported (probably < 20 bytes or so), which would
be less than the size of the data needed for current SHA1 collision be less than the size of the data needed for current SHA1 collision
attacks. Presumably aa preimage attack would need a similar amount of attacks. Presumably aa chosen-prefix attack would need a similar amount of
data. data.
* It might be possible to embed colliding data in a specially constructed * It might be possible to embed colliding data in a specially constructed