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Civil War Book Review

Oblivious transfer for secure communication

Abhishek Parakh

Published Sep 28, 2007• 0 citations

Abstract

Over the past four decades, computational power and algorithmic strategies have advanced tremendously resulting in an enormous increase in the key sizes required for secure cryptosystems such as RSA. At the same time, the electronic devices have grown smaller and portable requiring algorithms running on them to be optimized in size and efficiency while providing security, at least, equivalent to that provided on a typical desktop computer. As a result, the industry is moving towards newer cryptosystems such as ECC and NTRU that are well suited for resource constrained environments. While, ECC claims to provide security equivalent to that of RSA for a fraction of key size, NTRU is inherently suited for embedded systems technology. However, implementation of new cryptosystems requires the development of protocols analogous to those developed using older cryptosystems. In this thesis, we fulfill a part of this requirement by providing protocols for Oblivious Transfer using ECC and NTRU. Oblivious Transfer, in turn, has applications in simultaneous contract signing, digital certified mail, simultaneous exchange of secrets, secure multiparty computations, private information retrieval, etc. Furthermore, we introduce the idea of basing Oblivious Transfer on public-key exchange protocols. The presentation in the thesis uses Diffie-Hellman Key Exchange, but the scheme is generalizable to any cryptosystem that has a public-key exchange strategy. In fact, our proposal may especially be suited for Quantum Cryptography where the security of key exchange protocols has been proven.

DOI: 10.31390/gradschool_theses.3382

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Over the past four decades, computational power and algorithmic strategies have advanced tremendously resulting in an enormous increase in the key sizes required for secure cryptosystems such as RSA. At the same time, the electronic devices have grown smaller and portable requiring algorithms running on them to be optimized in size and efficiency while providing security, at least, equivalent to that provided on a typical desktop computer. As a result, the industry is moving towards newer cryptosystems such as ECC and NTRU that are well suited for resource constrained environments. While, ECC claims to provide security equivalent to that of RSA for a fraction of key size, NTRU is inherently suited for embedded systems technology. However, implementation of new cryptosystems requires the development of protocols analogous to those developed using older cryptosystems. In this thesis, we fulfill a part of this requirement by providing protocols for Oblivious Transfer using ECC and NTRU. Oblivious Transfer, in turn, has applications in simultaneous contract signing, digital certified mail, simultaneous exchange of secrets, secure multiparty computations, private information retrieval, etc. Furthermore, we introduce the idea of basing Oblivious Transfer on public-key exchange protocols. The presentation in the thesis uses Diffie-Hellman Key Exchange, but the scheme is generalizable to any cryptosystem that has a public-key exchange strategy. In fact, our proposal may especially be suited for Quantum Cryptography where the security of key exchange protocols has been proven.

The standard public-key cryptosystems used today relies mathematical problems that require a lot of computing force to solve, so much that, with the right parameters, they are computationally unsolvable. But there are quantum algorithms that are able to solve these problems in much shorter time. These quantum algorithms have been known for many years, but have only been a problem in theory because of the lack of quantum computers. But with recent development in the building of quantum computers, the cryptographic world is looking for quantum-resistant replacements for today’s standard public-key cryptosystems. Public-key cryptosystems based on lattices are possible replacements. This thesis presents several possible candidates for new standard public-key cryptosystems, mainly NTRU and ring-LWE-based systems. The latticebased cryptosystems are shown to be very fast and have strong, provable security against quantum computers, but are a lot more complicated than RSA and Diffie-Hellman.

Quantum entanglement is a phenomenon available only at nanometer scale. In this paper, we show how quantum entanglement can be used to build cryptographic primitives such as oblivious transfer. In addition to studying the protocol itself, we also show how to realize some applications based on our proposal. These include typical e-business applications such as contract signing, certified mail, simultaneous secret exchange, secure transaction and remote coin flip. Unlike classical oblivious transfer, the security of this protocol is based on physical laws, instead of any unproven mathematic conjecture. As a result, our proposal provides unconditional security for e-business

Key-exchange protocols have been overlooked as a possible means for implementing oblivious transfer (OT). In this article, we present protocols for mutual exchange of secrets, 1-out-of-2 OT and coin-flipping similar to the Diffie-Hellman protocol using the idea of obliviously exchanging encryption keys. Since the Diffie-Hellman scheme is widely used, our protocol may provide a useful alternative to the conventional methods for implementation of oblivious transfer and a useful primitive in building larger cryptographic schemes.

The Oblivious Transfer (OT) protocol is a privacy-preserving two-way communication protocol important for building secure multiparty computations. To exchange symmetric keys, this protocol is typically based on the Rivest—Shamir—Adleman (RSA) or Diffie—Hellman (DH) cryptographic systems, which are used for encryption during the message-encryption phase. However, in existing OT protocols, the generation of multiple pairs of public and private keys and data computations are time-consuming. Using bijective functions to transform the ciphertext within the same ciphertext domain can ensure indistinguishability after decryption and reduce the computational complexity. In the semi-honest model, a ciphertext obfuscation-based OT protocol framework is proposed and OT protocols are instantiated based on RSA and DH within this framework. Compared with RSA-based encryption schemes, the proposed protocol requires only one pair of public and private keys. When the number of public and private keys is reduced to one, the receiver can use the public key in the digital certificate of the sender to implement the OT protocol using an identity authentication function. Compared with the OT protocol based on the DH key exchange, this protocol has a small data transmission volume and low computational complexity. Experimental results show that, compared with existing OT protocols, the efficiency of instantiated protocols in the key exchange stage can be improved by at least 30%. Moreover, this protocol can be used as a basic protocol for privacy set intersections, obfuscation circuits, and OT extension protocols.

Oblivious transfer (OT) is the most fundamental process in cryptosystems and serves as the basic building block for implementing protocols, such as the secure multi-party computation and the fair electronic contract. However, since most implementations of the Internet of Things are time-sensitive, existing works that are based on traditional public cryptosystems are not efficient or secure under quantum machine attacks. In this paper, we argued that the fastest known 1-out-of-n oblivious transfer (OTn1) protocol, which was proposed by Chou, cannot achieve semantic security and is time-consuming due to exponent arithmetic of large parameters. Utilizing NTRUEncrypt and OT extension, we devised a one-round postquantum secure OTn1protocol that is also proved to be active and adaptively secure under the universal composability framework. Compared with Chou's protocol, the computational overheads of our scheme are approximately 6 and 1.7 times smaller on the sender and receiver sides, in line with the standard security level.