Entries Tagged "encryption"

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Dropbox Security

I haven’t written about Dropbox’s security problems; too busy with the book. But here’s an excellent summary article from The Economist.

The meta-issue is pretty simple. If you expect a cloud provider to do anything more interesting than simply store your files for you and give them back to you at a later date, they are going to have to have access to the plaintext. For most people—Gmail users, Google Docs users, Flickr users, and so on—that’s fine. For some people, it isn’t. Those people should probably encrypt their files themselves before sending them into the cloud.

EDITED TO ADD (6/13): Another security issue with Dropbox.

Posted on May 23, 2011 at 6:47 AM •

"Schneier's Law"

Back in 1998, I wrote:

Anyone, from the most clueless amateur to the best cryptographer, can create an algorithm that he himself can’t break.

In 2004, Cory Doctorow called this Schneier’s law:

…what I think of as Schneier’s Law: “any person can invent a security system so clever that she or he can’t think of how to break it.”

The general idea is older than my writing. Wikipedia points out that in The Codebreakers, David Kahn writes:

Few false ideas have more firmly gripped the minds of so many intelligent men than the one that, if they just tried, they could invent a cipher that no one could break.

The idea is even older. Back in 1864, Charles Babbage wrote:

One of the most singular characteristics of the art of deciphering is the strong conviction possessed by every person, even moderately acquainted with it, that he is able to construct a cipher which nobody else can decipher.

My phrasing is different, though. Here’s my original quote in context:

Anyone, from the most clueless amateur to the best cryptographer, can create an algorithm that he himself can’t break. It’s not even hard. What is hard is creating an algorithm that no one else can break, even after years of analysis. And the only way to prove that is to subject the algorithm to years of analysis by the best cryptographers around.

And here’s me in 2006:

Anyone can invent a security system that he himself cannot break. I’ve said this so often that Cory Doctorow has named it “Schneier’s Law”: When someone hands you a security system and says, “I believe this is secure,” the first thing you have to ask is, “Who the hell are you?” Show me what you’ve broken to demonstrate that your assertion of the system’s security means something.

And that’s the point I want to make. It’s not that people believe they can create an unbreakable cipher; it’s that people create a cipher that they themselves can’t break, and then use that as evidence they’ve created an unbreakable cipher.

EDITED TO ADD (4/16): This is an example of the Dunning-Kruger effect, named after the authors of this paper: “Unskilled and Unaware of It: How Difficulties in recognizing One’s Own Incompetence Lead to Inflated Self-Assessments.”

Abstract: People tend to hold overly favorable views of their abilities in many social and intellectual domains. The authors suggest that this overestimation occurs, in part, because people who are unskilled in these domains suffer a dual burden: Not only do these people reach erroneous conclusions and make unfortunate choices, but their incompetence robs them of the metacognitive ability to realize it. Across 4 studies, the authors found that participants scoring in the bottom quartile on tests of humor, grammar, and logic grossly overestimated their test performance and ability. Although their test scores put them in the 12th percentile, they estimated themselves to be in the 62nd. Several analyses linked this miscalibration to deficits in metacognitive skill, or the capacity to distinguish accuracy from error. Paradoxically, improving the skills of participants, and thus increasing their metacognitive competence, helped them recognize the limitations of their abilities.

EDITED TO ADD (4/18): If I have any contribution to this, it’s to generalize it to security systems and not just to cryptographic algorithms. Because anyone can design a security system that he cannot break, evaluating the security credentials of the designer is an essential aspect of evaluating the system’s security.

Posted on April 15, 2011 at 1:45 PM • View Comments

How Peer Review Doesn't Work

In this amusing story of a terrorist plotter using pencil-and-paper cryptography instead of actually secure cryptography, there’s this great paragraph:

Despite urging by the Yemen-based al Qaida leader Anwar Al Anlaki, Karim also rejected the use of a sophisticated code program called “Mujhaddin Secrets”, which implements all the AES candidate cyphers, “because ‘kaffirs’, or non-believers, know about it so it must be less secure”.

Posted on March 30, 2011 at 7:14 AM • View Comments

Detecting Words and Phrases in Encrypted VoIP Calls

Interesting:

Abstract: Although Voice over IP (VoIP) is rapidly being adopted, its security implications are not yet fully understood. Since VoIP calls may traverse untrusted networks, packets should be encrypted to ensure confidentiality. However, we show that it is possible to identify the phrases spoken within encrypted VoIP calls when the audio is encoded using variable bit rate codecs. To do so, we train a hidden Markov model using only knowledge of the phonetic pronunciations of words, such as those provided by a dictionary, and search packet sequences for instances of specified phrases. Our approach does not require examples of the speaker’s voice, or even example recordings of the words that make up the target phrase. We evaluate our techniques on a standard speech recognition corpus containing over 2,000 phonetically rich phrases spoken by 630 distinct speakers from across the continental United States. Our results indicate that we can identify phrases within encrypted calls with an average accuracy of 50%, and with accuracy greater than 90% for some phrases. Clearly, such an attack calls into question the efficacy of current VoIP encryption standards. In addition, we examine the impact of various features of the underlying audio on our performance and discuss methods for mitigation.

EDITED TO ADD (4/13): Full paper. I wrote about this in 2008.

Posted on March 24, 2011 at 12:46 PM • View Comments

Eavesdropping on GSM Calls

It’s easy and cheap:

Speaking at the Chaos Computer Club (CCC) Congress in Berlin on Tuesday, a pair of researchers demonstrated a start-to-finish means of eavesdropping on encrypted GSM cellphone calls and text messages, using only four sub-$15 telephones as network “sniffers,” a laptop computer, and a variety of open source software.

The encryption is lousy:

Several of the individual pieces of this GSM hack have been displayed before. The ability to decrypt GSM’s 64-bit A5/1 encryption was demonstrated last year at this same event, for instance. However, network operators then responded that the difficulty of finding a specific phone, and of picking the correct encrypted radio signal out of the air, made the theoretical decryption danger minimal at best.

But:

As part of this background communication, GSM networks send out strings of identifying information, as well as essentially empty “Are you there?” messages. Empty space in these messages is filled with buffer bytes. Although a new GSM standard was put in place several years ago to turn these buffers into random bytes, they in fact remain largely identical today, under a much older standard.

This allows the researchers to predict with a high degree of probability the plain-text content of these encrypted system messages. This, combined with a two-terabyte table of precomputed encryption keys (a so-called rainbow table), allows a cracking program to discover the secret key to the session’s encryption in about 20 seconds.

Did you notice that? A two-terabyte rainbow table. A few years ago, that kind of storage was largely theoretical. Now it’s both cheap and portable.

Posted on January 5, 2011 at 6:20 AM • View Comments

Proprietary Encryption in Car Immobilizers Cracked

This shouldn’t be a surprise:

Karsten Nohl’s assessment of dozens of car makes and models found weaknesses in the way immobilisers are integrated with the rest of the car’s electronics.

The immobiliser unit should be connected securely to the vehicle’s electronic engine control unit, using the car’s internal data network. But these networks often use weaker encryption than the immobiliser itself, making them easier to crack.

What’s more, one manufacturer was even found to use the vehicle ID number as the supposedly secret key for this internal network. The VIN, a unique serial number used to identify individual vehicles, is usually printed on the car. “It doesn’t get any weaker than that,” Nohl says.

Posted on December 23, 2010 at 2:02 PM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.