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+The fetch and push protocols are not designed to prevent one side from
+stealing data from the other repository that was not intended to be
+shared. If you have private data that you need to protect from a malicious
+peer, your best option is to store it in another repository. This applies
+to both clients and servers. In particular, namespaces on a server are not
+effective for read access control; you should only grant read access to a
+namespace to clients that you would trust with read access to the entire
+The known attack vectors are as follows:
+. The victim sends "have" lines advertising the IDs of objects it has that
+ are not explicitly intended to be shared but can be used to optimize the
+ transfer if the peer also has them. The attacker chooses an object ID X
+ to steal and sends a ref to X, but isn't required to send the content of
+ X because the victim already has it. Now the victim believes that the
+ attacker has X, and it sends the content of X back to the attacker
+ later. (This attack is most straightforward for a client to perform on a
+ server, by creating a ref to X in the namespace the client has access
+ to and then fetching it. The most likely way for a server to perform it
+ on a client is to "merge" X into a public branch and hope that the user
+ does additional work on this branch and pushes it back to the server
+ without noticing the merge.)
+. As in #1, the attacker chooses an object ID X to steal. The victim sends
+ an object Y that the attacker already has, and the attacker falsely
+ claims to have X and not Y, so the victim sends Y as a delta against X.
+ The delta reveals regions of X that are similar to Y to the attacker.