Paper: Xiao Shaun Wang and S. Dov Gordon and Allen McIntosh and Jonathan Katz, Secure Computation of MIPS Machine Code. In 21st European Symposium on Research in Computer Security (ESORICS), 2016.

In a paper to be presented at USENIX Security 2016, we consider a refined cost model and formalize the cut-and-choose parameter selection problem as a constrained optimization problem. We analyze “cut-and-choose games” and show equilibrium strategies
for the parties in these games. We then show how our methodology can be applied to improve the efficiency of three representative categories of secure-computation protocols based on cut-and-choose. We show improvements of up to an-order-of-magnitude in terms of bandwidth, and 12–106% in terms of total time.

Paper: Ruiyu Zhu, Yan Huang, Jonathan Katz, and abhi shelat. The Cut-and-Choose Game and its Application to Cryptographic Protocols. USENIX Security Symposium, 2016.

Source code of our game solvers: https://github.com/cut-n-choose

Samee Zahur presented the results at IEEE Symposium on Security and Privacy (“Oakland”) 2016. The full paper is:

Samee Zahur, Xiao Wang, Mariana Raykova, Adrià Gascón, Jack Doerner, David Evans, Jonathan Katz. Revisiting Square-Root ORAM Efficient Random Access in Multi-Party Computation. In 37th IEEE Symposium on Security and Privacy (“Oakland”). San Jose, CA. 23-25 May 2016.

For more (including source code and benchmarks), see https://oblivc.org/sqoram/.

Abstract. The well-known classical constructions of garbled circuits use four ciphertexts per gate, although various methods have been proposed to reduce this cost. The best previously known methods for optimizing AND gates (two ciphertexts; Pinkas et al., ASIACRYPT 2009) and XOR gates (zero ciphertexts; Kolesnikov & Schneider, ICALP 2008) were incompatible, so most implementations used the best known method compatible with free-XOR gates (three ciphertexts; Kolesnikov & Schneider, ICALP 2008). In this work we show how to simultaneously garble AND gates using two ciphertexts and XOR gates using zero ciphertexts, resulting in smaller garbled circuits than any prior scheme. The main idea behind our construction is to break an AND gate into two half-gates — AND gates for which one party knows one input. Each half-gate can be garbled with a single ciphertext, so our construction uses two ciphertexts for each AND gate while being compatible with free-XOR gates. The price for the reduction in size is that the evaluator must perform two cryptographic operations per AND gate, rather than one as in previous schemes. We experimentally demonstrate that our garbling scheme leads to an overall decrease in time (up to 25%), bandwidth (up to 33%), and energy use (up to 20%) over several benchmark applications. We also initiate a study of lower bounds for garbled gate size, and show that our construction is optimal for a large class of garbling schemes encompassing all known practical garbling techniques.

Samee’s solution was built using Obliv-C, a language for data-oblivious computation.

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]

Full paper (15 pages): [PDF]

Project: MightBeEvil.com/netlist

Code: http://github.com/samee/netlist

Yan Huang, Jonathan Katz, and David Evans. Quid Pro Quo-tocols: Strengthening Semi-Honest Protocols with Dual Execution. In 33rd IEEE Symposium on Security and Privacy (“Oakland” 2012), San Francisco, CA. 20-23 May 2012. [PDF, 13 pages]

Yan Huang will present the paper at the Oakland conference (which will be held in San Francisco for the first time, after being in Berkeley/Oakland for the first 32 years!) in May.

Abstract: Known protocols for secure two-party computation that are designed to provide full security against malicious behavior are significantly less efficient than protocols intended only to thwart semi-honest adversaries. We present a concrete design and implementation of protocols achieving security guarantees that are much stronger than are possible with semi-honest protocols, at minimal extra cost. Specifically, we consider protocols in which a malicious adversary may learn a single (arbitrary) bit of additional information about the honest party’s input. Correctness of the honest party’s output is still guaranteed. Adapting prior work of Mohassel and Franklin, the basic idea in our protocols is to conduct two separate runs of a (specific) semi-honest, garbled-circuit protocol, with the parties swapping roles, followed by an inexpensive secure equality test. We provide a rigorous definition and prove that this protocol leaks no more than one additional bit against a malicious adversary. In addition, we propose some enhancements to reduce the overall information a cheating adversary learns. Our experiments show that protocols meeting this security level can be implemented at cost very close to that of protocols that only achieve semi-honest security. Our results indicate that this model enables the large-scale, practical applications possible within the semi-honest security model, while providing dramatically stronger security guarantees.

Full paper (13 pages): [PDF]

Project site: MightBeEvil.com

The paper develops three circuit designs for securely computing the intersection of two sets, where each set is the private input from one protocol participant. We show that for many scenarios, protocols built using only generic garbled circuit secure computation techniques can be competitive with the best custom-designed protocols for private set intersection.

Yan Huang will present the paper at NDSS in San Diego, in February 2012.