2
$\begingroup$

Consider we have three parties,namely client $A$, client $B$ and a server. Client $B$ and the server can be malicious, but we do not allow the adversary to simultaneously corrupt the server and client $B$ (similar to [1]). The scenario is that both clients outsource their private data to the server. Then they ask the server to do computation and send back the result and a proof of computation correctness to client B. I have designed a protocol that satisfy the above properties but the malicious server may send an incomplete result. This can be detected by client B but after that if client $B$ proceeds it can learn client $A$'s data (and this is not desirable).

Question: Based on the above security model, is client $B$ allowed to take further action to figure out the other client's data, after it detects the server's malicious behavior?

Edit: TBN: The outsourced data is not leaked to the malicious server.

[1]. http://research.microsoft.com/pubs/194141/sapsi2.pdf

$\endgroup$
  • 1
    $\begingroup$ I would say that under that security model, if you are assuming the server is being malicious, then client B cannot proceed with any malicious action. In other words, that would be equivalent, in the security proof, to an adversary who is corrupting both the server and client B at the same time, which contradicts your initial assumptions. $\endgroup$ – cygnusv May 7 '15 at 10:45
1
$\begingroup$

$A$ has outsourced it's private data to the server, right? In that case $A$'s private data has already been leaked to the adversary when the server was corrupted. So there is no added leakage in $B$ also learning this data. In fact since only one of $B$ and the server can be corrupted (assuming static corruptions) we can conclude that $B$ is honest, and there is really no problem.

$\endgroup$
  • $\begingroup$ "A's private data has already been leaked to the adversary when the server was corrupted" : I would say no, it's protected from the server, thus there's no data leakage to the server. However, I should have mentioned that in the question. $\endgroup$ – user13676 May 7 '15 at 10:55
  • 1
    $\begingroup$ Even then there is probably no problem. The argument that $B$ must be honest still holds. So $B$ learning $A$'s data should not be a problem, since what we are trying to do is to protect ourselves from the adversary, not the honest parties. $\endgroup$ – Guut Boy May 7 '15 at 12:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.