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communication complexity on the buyer\'s side and $O(n)$ communication cost on the vendor\'s side, which is so far the best known in the literature.
In this paper we propose a new technique that allows us to to construct a non-malleable protocol with only a single ``slot\", and to improve in at least one aspect over each of the previously proposed protocols. Two direct byproducts of our new ideas are a four round non-malleable commitment and a four round non-malleable zero-knowledge argument, the latter matching the round complexity of the best known zero-knowledge argument (without the non-malleability requirement). The protocols are based on the existence of one-way permutations (or alternatively one-way functions with an extra round) and admit very efficient instantiations via standard homomorphic commitments and sigma protocols.
Our analysis relies on algebraic reasoning, and makes use of error correcting codes in order to ensure that committers\' tags differ in many coordinates. One way of viewing our construction is as a method for combining many atomic sub-protocols in a way that simultaneously amplifies soundness and non-malleability, thus requiring much weaker guarantees to begin with, and resulting in a protocol which is much trimmer in complexity compared to the existing ones.
knowledge in the random oracle model from general sigma-protocols. Our
construction is secure against quantum adversaries. Prior
constructions (by Fiat-Shamir and by Fischlin) are only known to be
secure against classical adversaries, and Ambainis, Rosmanis, Unruh
(FOCS 2014) gave evidence that those constructions might not be secure
against quantum adversaries in general.
To prove security of our constructions, we additionally develop new
techniques for adaptively programming the quantum random oracle.
from Ideal lattices. The protocol
is simple since it does not involve any other cryptographic primitives
to achieve authentication (e.g., signatures). This allows us
to establish a security proof solely based on the hardness of
the well-known ring-LWE problems, thus on some hard lattice problems in the worst-case (e.g., SVP and SIVP). We give the security proof of the proposed
AKE protocol in an enhanced variant of the original
Bellare-Rogaway (BR) model,
which additionally captures weak Perfect Forward Secrecy (wPFS),
in the random oracle (RO) model.
To be considered for the position the applicant should have a PhD degree in Computer Science. Some postdoctoral research experience is an asset. Good oral and written communication skills and the ability to work on a team project are essential.
This is a full-time position, available as of October 1, 2014 and will initially be for one year, with the possibility of renewal for three more years. Salary will depend upon the qualifications and experience of the successful applicant.
Interested applicants should submit a covering letter, along with a resume, and the name, address, phone and e-email addresses of three academic references. Review of applications will begin in August 1, 2014 and will continue until the position is filled.
The position is within the cryptography and information security group in the HASLab.
The group is actively working on: provable security, domain-specific languages and software development tools for cryptography, efficient implementation of cryptographic software, and formal verification of cryptographic proofs and implementations.
We are looking for a highly motivated researcher with a recent Ph.D. and background in at least one of the following fields:
efficient implementation of cryptography,
programming languages and verification,
and an interest in carrying out research at their intersection.
The position starts from November 2014. The salary is around 18K euros per year after tax. The working language is English.
Applications should arrive no later than September 19, 2014 and should include a CV, a cover letter, and the names and contact details for two references.