Entries Tagged "academic papers"

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"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

Federated Authentication

New paper by Ross Anderson: “Can We Fix the Security Economics of Federated Authentication?“:

There has been much academic discussion of federated authentication, and quite some political manoeuvring about ‘e-ID’. The grand vision, which has been around for years in various forms but was recently articulated in the US National Strategy for Trustworthy Identities in Cyberspace (NSTIC), is that a single logon should work everywhere [1]. You should be able to use your identity provider of choice to log on anywhere; so you might use your driver’s license to log on to Gmail, or use your Facebook logon to file your tax return. More restricted versions include the vision of governments of places like Estonia and Germany (and until May 2010 the UK) that a government-issued identity card should serve as a universal logon. Yet few systems have been fielded at any scale.

In this paper I will briefly discuss the four existing examples we have of federated authentication, and then go on to discuss a much larger, looming problem. If the world embraces the Apple vision of your mobile phone becoming your universal authentication device ­ so that your phone contains half-a dozen credit cards, a couple of gift cards, a dozen coupons and vouchers, your AA card, your student card and your driving license, how will we manage all this? A useful topic for initial discussion, I argue, is revocation. Such a phone will become a target for bad guys, both old and new. What happens when someone takes your phone off you at knifepoint, or when it gets infested with malware? Who do you call, and what will they do to make the world right once more?

Blog post.

Posted on March 29, 2011 at 6:43 AM • View Comments

Identifying Tor Users Through Insecure Applications

Interesting research: “One Bad Apple Spoils the Bunch: Exploiting P2P Applications to Trace and Profile Tor Users“:

Abstract: Tor is a popular low-latency anonymity network. However, Tor does not protect against the exploitation of an insecure application to reveal the IP address of, or trace, a TCP stream. In addition, because of the linkability of Tor streams sent together over a single circuit, tracing one stream sent over a circuit traces them all. Surprisingly, it is unknown whether this linkability allows in practice to trace a significant number of streams originating from secure (i.e., proxied) applications. In this paper, we show that linkability allows us to trace 193% of additional streams, including 27% of HTTP streams possibly originating from “secure” browsers. In particular, we traced 9% of Tor streams carried by our instrumented exit nodes. Using BitTorrent as the insecure application, we design two attacks tracing BitTorrent users on Tor. We run these attacks in the wild for 23 days and reveal 10,000 IP addresses of Tor users. Using these IP addresses, we then profile not only the BitTorrent downloads but also the websites visited per country of origin of Tor users. We show that BitTorrent users on Tor are over-represented in some countries as compared to BitTorrent users outside of Tor. By analyzing the type of content downloaded, we then explain the observed behaviors by the higher concentration of pornographic content downloaded at the scale of a country. Finally, we present results suggesting the existence of an underground BitTorrent ecosystem on Tor.

Posted on March 25, 2011 at 6:38 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

Folk Models in Home Computer Security

This is a really interesting paper: “Folk Models of Home Computer Security,” by Rick Wash. It was presented at SOUPS, the Symposium on Usable Privacy and Security, last year.

Abstract:

Home computer systems are frequently insecure because they are administered by untrained, unskilled users. The rise of botnets has amplified this problem; attackers can compromise these computers, aggregate them, and use the resulting network to attack third parties. Despite a large security industry that provides software and advice, home computer users remain vulnerable. I investigate how home computer users make security-relevant decisions about their computers. I identify eight ‘folk models’ of security threats that are used by home computer users to decide what security software to use, and which security advice to follow: four different conceptualizations of ‘viruses’ and other malware, and four different conceptualizations of ‘hackers’ that break into computers. I illustrate how these models are used to justify ignoring some security advice. Finally, I describe one reason why botnets are so difficult to eliminate: they have been cleverly designed to take advantage of gaps in these models so that many home computer users do not take steps to protect against them.

I’d list the models, but it’s more complicated than that. Read the paper.

Posted on March 22, 2011 at 7:12 AM • View Comments

Erasing Data from Flash Drives

“Reliably Erasing Data From Flash-Based Solid State Drives,” by Michael Wei, Laura M. Grupp, Frederick E. Spada, and Steven Swanson.

Abstract: Reliably erasing data from storage media (sanitizing the media) is a critical component of secure data management. While sanitizing entire disks and individual files is well-understood for hard drives, flash-based solid state disks have a very different internal architecture, so it is unclear whether hard drive techniques will work for SSDs as well.

We empirically evaluate the effectiveness of hard drive-oriented techniques and of the SSDs’ built-in sanitization commands by extracting raw data from the SSD’s flash chips after applying these techniques and commands. Our results lead to three conclusions: First, built-in commands are effective, but manufacturers sometimes implement them incorrectly. Second, overwriting the entire visible address space of an SSD twice is usually, but not always, sufficient to sanitize the drive. Third, none of the existing hard drive-oriented techniques for individual file sanitization are effective on SSDs.

This third conclusion leads us to develop flash translation layer extensions that exploit the details of flash memory’s behavior to efficiently support file sanitization. Overall, we find that reliable SSD sanitization requires built-in, verifiable sanitize operations.

News article. Video of talk.

Posted on March 1, 2011 at 6:29 AM • View Comments

Trojan Steals Credit Card Numbers

It’s only a proof of concept, but it’s scary nonetheless. It’s a Trojan for Android phones that looks for credit-card numbers, either typed or spoken, and relays them back to its controller.

Software released for Android devices has to request permissions for each system function it accesses—with apps commonly requesting access to the network, phone call functionality, internal and external storage devices, and miscellaneous hardware functions such as the backlight, LED, or microphone. These requests are grouped into categories and presented to the user at the point of installation—helping to minimise the chance of a Trojan slipping by.

Soundminer takes a novel approach to these restrictions, by only requesting access to ‘Phone calls,’ to read phone state and identity, ‘Your personal information,’ to read contact data, and ‘Hardware controls’ to record audio—none of which will ring alarm bells if the app is marketed as a voice recording tool.

Research paper here. YouTube demo. Another blog post. Research paper; section 7.2 describes some defenses, but I’m not really impressed by any of them.

Posted on January 29, 2011 at 7:45 AM • View Comments

Hacking Tamper-Evident Devices

At the Black Hat conference lasts week, Jamie Schwettmann and Eric Michaud presented some great research on hacking tamper-evident seals.

Jamie Schwettmann and Eric Michaud of i11 Industries went through a long list of tamper evident devices at the conference here and explained, step-by-step, how each seal can be circumvented with common items, such as various solvents, hypodermic needles, razors, blow driers, and in more difficult cases with the help of tools such as drills.

Tamper-evident devices may be as old as civilization, and today are used in everyday products such as aspirin containers’ paper seals. The more difficult devices may be bolt locks designed to secure shipping containers, or polycarbonate locks designed to shatter if cut.

But they all share something in common: They can be removed and the anti-tampering device reassembled.

Here’s their paper, and here are the slides from their presentation. (These two direct download links from GoogleDocs also work.) There was more information in the presentation than in either the paper or the PowerPoint slides. If the video ever gets online, I’ll link to it in this post.

Posted on January 24, 2011 at 1:20 PM • View Comments

The Legality of the Certificate Authority Trust Model

Interesting research:

We looked at the standard legal documents issued by the certificate authorities or “CAs,” including exemplar Subscriber Agreements (agreements between CAs and website operators); “Certification Practice Statements” (statements by CAs outlining their business practices); and Relying Party Agreements (purported agreements between CAs and “relying parties,” such as end-users). What we found was surprising:

  • “Relying Party Agreements” purport to bind end-users to their terms despite the apparent absence of any mechanism to either affirmatively alert the end-user as to the existence of the supposed Agreements or afford the end-user an opportunity to register his or her acceptance or rejection of the Agreements’ terms
  • Certification Practice Statements that suffer from the same problem (i.e. no affirmative notice to the end-user and no meaningful opportunity for acceptance or rejection of terms)

There were other issues as well. For example, the Relying Party Agreements and Certification Practice Statements set forth various obligations on the part of end-users (i.e. “relying parties”) such as: the requirement that end-users make an independent determination of whether it is reasonable to trust a website offering a secure connection (isn’t that the whole point of having a CA, so that the end-user doesn’t have to do that?); the requirement that the end-user be familiar with the crypto software and processes used to carry out the authentication process; and the end-user’s duty to indemnify and hold harmless the CA in the event of legal claims by third parties.

Paper here.

EDITED TO ADD (2/10)> Matt Blaze on CAs.

Posted on January 21, 2011 at 5:31 AM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.