The problem, Médard explains, is that information-theoretic analyses of secure systems have generally used the wrong notion of entropy. They relied on so-called Shannon entropy, named after the founder of information theory, Claude Shannon, who taught at MIT from 1956 to 1978.
Shannon entropy is based on the average probability that a given string of bits will occur in a particular type of digital file. In a general-purpose communications system, that’s the right type of entropy to use, because the characteristics of the data traffic will quickly converge to the statistical averages. Although Shannon’s seminal 1948 paper dealt with cryptography, it was primarily concerned with communication, and it used the same measure of entropy in both discussions.
But in cryptography, the real concern isn’t with the average case but with the worst case. A codebreaker needs only one reliable correlation between the encrypted and unencrypted versions of a file in order to begin to deduce further correlations. In the years since Shannon’s paper, information theorists have developed other notions of entropy, some of which give greater weight to improbable outcomes. Those, it turns out, offer a more accurate picture of the problem of codebreaking.
When Médard, Duffy and their students used these alternate measures of entropy, they found that slight deviations from perfect uniformity in source files, which seemed trivial in the light of Shannon entropy, suddenly loomed much larger. The upshot is that a computer turned loose to simply guess correlations between the encrypted and unencrypted versions of a file would make headway much faster than previously expected.
“It’s still exponentially hard, but it’s exponentially easier than we thought,” Duffy says. One implication is that an attacker who simply relied on the frequencies with which letters occur in English words could probably guess a user-selected password much more quickly than was previously thought. “Attackers often use graphics processors to distribute the problem,” Duffy says. “You’d be surprised at how quickly you can guess stuff.”
Has Hurricane Sandy inaugurated a new age of climate fueled superstorms? Environmentalist Peter Sinclair interviews hurricane expert Dr. Kerry Emanuel of MIT, and Dr. Jason Box of the Byrd Polar Center.
Emanuel 2007, Environmental Factors Affecting Tropical Cyclone Power Dissipation
This is the age of miracles and wonders. Tonight’s case in point: the MIT Media Lab’s new imaging system that takes exposures at a trillion frames per second, allowing researchers to actually visualize light traveling through space.
Human beings are now looking at photons in motion. Unbelievable. This video shows a nanosecond pulse of laser light traveling through a plastic Coca-Cola bottle:
Here’s some potentially very exciting news from MIT, where a breakthrough in battery design could lead to truly viable electric cars: New battery design could give electric vehicles a jolt.
A radically new approach to the design of batteries, developed by researchers at MIT, could provide a lightweight and inexpensive alternative to existing batteries for electric vehicles and the power grid. The technology could even make “refueling” such batteries as quick and easy as pumping gas into a conventional car.
The new battery relies on an innovative architecture called a semi-solid flow cell, in which solid particles are suspended in a carrier liquid and pumped through the system. In this design, the battery’s active components — the positive and negative electrodes, or cathodes and anodes — are composed of particles suspended in a liquid electrolyte. These two different suspensions are pumped through systems separated by a filter, such as a thin porous membrane.
Apparently, being accepted to MIT is no indicator of intelligence: MIT student ‘lucky to be alive’ after fake bomb prank.
An MIT student with a fake bomb strapped to her chest was arrested at gunpoint today at Logan International Airport and later claimed it was artwork, officials said.
Star Simpson, 19, had a computer circuit board and wiring in plain view over a black hooded sweat shirt she was wearing, said State Police Maj. Scott Pare, the commanding officer at the airport. “She said that it was a piece of art and she wanted to stand out on career day,” Pare said at a news conference. “She claims that it was just art, and that she was proud of the art and she wanted to display it.”
The device had wires connected to a battery, allowing it to light up, he said. Simpson also had Play-Doh in her hands, he said.
Simpson was charged with disturbing the peace and possessing a hoax device, and was to be arraigned in East Boston District Court later today.
“I’m shocked and appalled that somebody would wear this type of device to an airport,” Pare said. Simpson was “extremely lucky she followed the instructions or deadly force would have been used,” Pare said. “She’s lucky to be in a cell as opposed to the morgue.”