Jefferson's Wheel

Security exploits nearly always stem from attackers finding ways to violate assumptions system implementers relied upon. As a simple example, consider a classic buffer overflow attack which is possible because the implementers assumed (perhaps implicitly) that the size of some data could not exceed the buffer size, but an attacker found a way to create an input that violates that assumption.

In this work, joint with colleagues at Microsoft Research, we consider the implicit assumptions upon which secure use of single sign-on SDKs depends. Our study of three important authentication and authorization SDKs (including Facebook’s) supports the need for systematically explicating SDKs to uncover these assumptions. We found assumptions that were critical to secure use of the SDKs, but that were not clearly documented and were subtle enough to be missed by the majority of tested apps.

We advocate that a systematic explication process for uncovering these assumptions should be part of the engineering process for developing security-critical SDKs.

For details, see our paper:

Our paper on symmetric cut-and-choose is now available. The paper will be presented at CRYPTO 2013 in August.

Abstract. Beginning with the work of Lindell and Pinkas, researchers have proposed several protocols for secure two-party computation based on the cut-and-choose paradigm. In existing instantiations of this paradigm, one party generates k garbled circuits; some fraction of those are “checked” by the other party, and the remaining fraction are evaluated. We introduce here the idea of symmetric cut-and-choose protocols, in which both parties generate k circuits to be checked by the other party. The main advantage of our technique is that k can be reduced by a factor of 3 while attaining the same statistical security level as in prior work. Since the number of garbled circuits dominates the costs of the protocol, especially as larger circuits are evaluated, our protocol is expected to run up to 3 times faster than existing schemes. Preliminary experiments validate this claim.

Full paper (16 pages): [PDF]