96 research outputs found
The Cryptographic Strength of Tamper-Proof Hardware
Tamper-proof hardware has found its way into our everyday life in various forms, be it SIM cards, credit cards or passports. Usually, a cryptographic key is embedded in these hardware tokens that allows the execution of simple cryptographic operations, such as encryption or digital signing. The inherent security guarantees of tamper-proof hardware, however, allow more complex and diverse applications
Hardening the Security of Server-Aided MPC Using Remotely Unhackable Hardware Modules
Garbling schemes are useful building blocks for enabling secure multi-party computation (MPC), but require considerable computational resources both for the garbler and the evaluator. Thus, they cannot be easily used in a resource-restricted setting, e.g. on mobile devices. To circumvent this problem, server-aided MPC can be used, where circuit garbling and evaluation are performed by one or more servers. However, such a setting introduces additional points of failure: The servers, being accessible over the network, are susceptible to remote hacks. By hacking the servers, an adversary may learn all secrets, even if the parties participating in the MPC are honest. In this work, we investigate how the susceptibility for such remote hacks in the server-aided setting can be reduced. To this end, we modularize the servers performing the computationally intensive tasks. By using data diodes, air-gap switches and other simple remotely unhackable hardware modules, we can isolate individual components during large parts of the protocol execution, making remote hacks impossible at these times. Interestingly, this reduction of the attack surface comes without a loss of efficiency
A Unified Approach to Constructing Black-box UC Protocols in Trusted Setup Models
We present a unified framework for obtaining black-box constructions of Universal Composable (UC) protocol in trusted setup models. Our result is analogous to the unified framework of Lin, Pass, and Venkitasubramaniam [STOC\u2709, Asiacrypt\u2712] that, however, only yields non-black-box constructions of UC protocols. Our unified framework shows that to obtain black-box constructions of UC protocols, it suffices to implement a special purpose commitment scheme that is, in particular, concurrently extractable using a given trusted setup. Using our framework, we improve black-box constructions in the common reference string and tamper-proof hardware token models by weakening the underlying computational and setup assumptions
On the Composability of Statistically Secure Random Oblivious Transfer
We show that random oblivious transfer protocols that are statistically secure according to a definition based on a list of information-theoretical properties are also statistically universally composable. That is, they are simulatable secure with an unlimited adversary, an unlimited simulator, and an unlimited environment machine. Our result implies that several previous oblivious transfer protocols in the literature that were proven secure under weaker, non-composable definitions of security can actually be used in arbitrary statistically secure applications without lowering the security
A Framework for Efficient Adaptively Secure Composable Oblivious Transfer in the ROM
Oblivious Transfer (OT) is a fundamental cryptographic protocol that finds a
number of applications, in particular, as an essential building block for
two-party and multi-party computation. We construct a round-optimal (2 rounds)
universally composable (UC) protocol for oblivious transfer secure against
active adaptive adversaries from any OW-CPA secure public-key encryption scheme
with certain properties in the random oracle model (ROM). In terms of
computation, our protocol only requires the generation of a public/secret-key
pair, two encryption operations and one decryption operation, apart from a few
calls to the random oracle. In~terms of communication, our protocol only
requires the transfer of one public-key, two ciphertexts, and three binary
strings of roughly the same size as the message. Next, we show how to
instantiate our construction under the low noise LPN, McEliece, QC-MDPC, LWE,
and CDH assumptions. Our instantiations based on the low noise LPN, McEliece,
and QC-MDPC assumptions are the first UC-secure OT protocols based on coding
assumptions to achieve: 1) adaptive security, 2) optimal round complexity, 3)
low communication and computational complexities. Previous results in this
setting only achieved static security and used costly cut-and-choose
techniques.Our instantiation based on CDH achieves adaptive security at the
small cost of communicating only two more group elements as compared to the
gap-DH based Simplest OT protocol of Chou and Orlandi (Latincrypt 15), which
only achieves static security in the ROM
Complete Primitives for Information-Theoretically Secure Two-Party Computation
This thesis contributes two results to the research area of secure two-party computation. The first result is a full combinatorial characterization of all cryptogates that are powerful enough to be used for implementation of arbitrary secure computations. The second result shows that any secure two-party computation can be based on a single reusable tamper-proof hardware token, although the receiver does not trust the token issuer
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