For small and midsize organizations, the outsourcing of demanding computational tasks to the cloud — huge banks of computers accessible over the Internet — can be much more cost-effective than buying their own hardware.
But it also poses a security risk: A malicious hacker could rent space on a cloud server and use it to launch programs that hijack legitimate applications, interfering with their execution.
In August, at the International Cryptology Conference, researchers from MIT and Israel's Technion and Tel Aviv University presented a new system that can quickly verify that a program running on the cloud is executing properly. That amounts to a guarantee that no malicious code is interfering with the program's execution.
The same system also protects the data used by applications running in the cloud, cryptographically ensuring that the user won't learn anything other than the immediate results of the requested computation. If, for instance, hospitals were pooling medical data in a huge database hosted on the cloud, researchers could look for patterns in the data without compromising patient privacy.
Although the paper reports new theoretical results, the researchers have also built working code that implements their system. At present, it works only with programs written in the C programming language, but adapting it to other languages should be straightforward.
The new work, like much current research on secure computation, requires that computer programs be represented as circuits. So the researchers' system includes a "circuit generator" that automatically converts C code to circuit diagrams. The circuits it produces, however, are much smaller than those produced by its predecessors, so by itself, the circuit generator may find other applications in cryptography.
Joining Chiesa on the paper are Madars Virza, also a graduate student in electrical engineering and computer science; the Technion's Daniel Genkin and Eli Ben-Sasson, who was a visiting professor at MIT for the past two years; and Tel Aviv University's Eran Tromer, who was a postdoc at MIT. The researchers' system implements a so-called zero-knowledge proof, a type of mathematical game invented by MIT professors Shafi Goldwasser and Silvio Micali and their colleague Charles Rackoff of the University of Toronto. In its cryptographic application, a zero-knowledge proof enables one of the game's players to prove to the other that he or she knows a secret key without actually divulging it.
But as its name implies, a zero-knowledge proof is a more general method for proving mathematical theorems — and the correct execution of a computer program can be redescribed as a theorem. So zero-knowledge proofs are by definition able to establish whether or not a computer program is executing correctly.
The problem is that existing implementations of zero-knowledge proofs — except in cases where they've been tailored to particular algorithms — take as long to execute as the programs they're trying to verify. That's fine for password verification, but not for a computation substantial enough that it might be farmed out to the cloud.
The researchers' innovation is a practical, succinct zero-knowledge proof for arbitrary programs. Indeed, it's so succinct that it can typically fit in a single data packet.Linear thinking
The problem, Virza says, is that "the current known constructions of the PCP theorem, though great in theory, have quite bad practical realizations." That's because the theory assumes that an adversary who's trying to produce a fraudulent proof has unbounded computational capacity. What Chiesa, Virza and their colleagues do instead is assume that the adversary is capable only of performing simple linear operations.
"This assumption is, of course, false in practice," Virza says. "So we use a cryptographic encoding to force the adversary to only linear evaluations. There is a way to encode numbers into such a form that you can add those numbers, but you can't do anything else. This is how we sidestep the inefficiencies of the PCP theorem."
Written by Larry Hardesty, MIT News Office
Andrew Carleen | EurekAlert!
Stable magnetic bit of three atoms
21.09.2017 | Sonderforschungsbereich 668
Drones can almost see in the dark
20.09.2017 | Universität Zürich
At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.
Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
25.09.2017 | Power and Electrical Engineering
25.09.2017 | Health and Medicine
25.09.2017 | Physics and Astronomy