| SECURITY |
| -------- |
| 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 |
| repository. |
| |
| 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. |
