Abstract. We describe an actively secure OT extension protocol in the random oracle model with efficiency very close to the passively secure IKNP protocol of Ishai et al. (Crypto 2003). For computational security parameter κ, our protocol requires κ base OTs, and is the first practical, actively secure protocol to match the cost of the passive IKNP extension in this regard. The added communication cost is only additive in O(κ), independent of the number of OTs being created, while the computation cost is essentially two finite field operations per extended OT. We present implementation results that show our protocol takes no more than 5% more time than the passively secure IKNP extension, in both LAN and WAN environments, and thus is essentially optimal with respect to the passive protocol.

Abstract. This paper describes a 1-out-of-N oblivious transfer (OT) extension protocol with active security, which achieves very low overhead on top of the passively secure protocol of Kolesnikov and Kumaresan (Crypto 2011). Our protocol obtains active security using a consistency check which requires only simple computation and has a communication overhead that is independent of the total number of OTs to be produced. We prove its security in both the random oracle model and the standard model, assuming a variant of correlation robustness. We describe an implementation, which demonstrates our protocol only costs around 5-30% more than the passively secure protocol. Random 1-out-of-N OT is a key building block in recent, very efficient, passively secure private set intersection (PSI) protocols. Our random OT extension protocol has the interesting feature that it even works when N is exponentially large in the security parameter, provided that the sender only needs to obtain polynomially many outputs. We show that this can be directly applied to improve the performance of PSI, allowing the core private equality test and private set inclusion subprotocols to be carried out using just a single OT each. This leads to a reduction in communication of up to 3 times for the main component of PSI.

Abstract. We extend the Tiny-OT two party protocol of Nielsen et al (CRYPTO 2012) to the case of n parties in the dishonest majority setting. This is done by presenting a novel way of transferring pairwise authentications into global authentications. As a by product we obtain a more efficient manner of producing globally authenticated shares, in the random oracle model, which in turn leads to a more efficient two party protocol than that of Nielsen et al.

Abstract. SPDZ, TinyOT and MiniMAC are a family of MPC protocols based on secret sharing with MACs, where a preprocessing stage produces multiplication triples in a finite field. This work describes new protocols for generating multiplication triples in fields of characteristic two using OT extensions. Before this work, TinyOT, which works on binary circuits, was the only protocol in this family using OT extensions. Previous SPDZ protocols for triples in large finite fields require somewhat homomorphic encryption, which leads to very inefficient runtimes in practice, while no dedicated preprocessing protocol for MiniMAC (which operates on vectors of small field elements) was previously known. Since actively secure OT extensions can be performed very efficiently using only symmetric primitives, it is highly desirable to base MPC protocols on these rather than expensive public key primitives. We analyze the practical efficiency of our protocols, showing that they should all perform favorably compared with previous works; we estimate our protocol for SPDZ triples in F 2 40 will perform around 2 orders of magnitude faster than the best known previous protocol.

We propose a new syndrome variety, which can be used to decode cyclic codes. We present also a generalization to erasure and error decoding. We can exhibit a polynomial whose roots give the error locations, once it has been specialized to a given syndrome. This polynomial has degree t in the variable corresponding to the error locations and its coefficients are polynomials in the syndromes.