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Joey Hess 2017-02-24 01:21:54 -04:00
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doc/todo/sha1_collision_embedding_in_git-annex_keys.mdwn
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@ -23,10 +23,21 @@ is enabled)
A few other potential problems:
* `*E` backends could embed sha1 collision data in a long filename
extension. It might be worth limiting the length
extension in a key.
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
attack is only a prefix attack; it does not allow creating two colliding
keys that contain two different SHA2 checksums. That would need a
preimage attack to be feasible.
It might be worth limiting the length
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
be less than the size of the data needed for current SHA1 collision attacks.
be less than the size of the data needed for current SHA1 collision
attacks. Presumably aa preimage attack would need a similar amount of
data.
* It might be possible to embed colliding data in a specially constructed
key name with an extra field in it, eg "SHA256-cXXXXXXXXXXXXXXX-...".
Need to review the code and see if such extra fields are allowed.