Entries Tagged "encryption"

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New Information on the Inventor of the One-Time Pad

Seems that the one-time pad was not first invented by Vernam:

He could plainly see that the document described a technique called the one-time pad fully 35 years before its supposed invention during World War I by Gilbert Vernam, an AT&T engineer, and Joseph Mauborgne, later chief of the Army Signal Corps.

[…]

The 1882 monograph that Dr. Bellovin stumbled across in the Library of Congress was “Telegraphic Code to Insure Privacy and Secrecy in the Transmission of Telegrams,” by Frank Miller, a successful banker in Sacramento who later became a trustee of Stanford University. In Miller’s preface, the key points jumped off the page:

“A banker in the West should prepare a list of irregular numbers to be called ‘shift numbers,'” he wrote. “The difference between such numbers must not be regular. When a shift-number has been applied, or used, it must be erased from the list and not be used again.”

It seems that Vernam was not aware of Miller’s work, and independently invented the one-time pad.

Another article. And the paper.

Posted on August 3, 2011 at 12:57 PM • View Comments

Breaking the Xilinx Virtex-II FPGA Bitstream Encryption

It’s a power-analysis attack, which makes it much harder to defend against. And since the attack model is an engineer trying to reverse-engineer the chip, it’s a valid attack.

Abstract: Over the last two decades FPGAs have become central components for many advanced digital systems, e.g., video signal processing, network routers, data acquisition and military systems. In order to protect the intellectual property and to prevent fraud, e.g., by cloning an FPGA or manipulating its content, many current FPGAs employ a bitstream encryption feature. We develop a successful attack on the bitstream encryption engine integrated in the widespread Virtex-II Pro FPGAs from Xilinx, using side-channel analysis. After measuring the power consumption of a single power-up of the device and a modest amount of o-line computation, we are able to recover all three different keys used by its triple DES module. Our method allows extracting secret keys from any real-world device where the bitstream encryption feature of Virtex-II Pro is enabled. As a consequence, the target product can be cloned and manipulated at will of the attacker. Also, more advanced attacks such as reverse engineering or the introduction of hardware Trojans become potential threats. As part of the side-channel attack, we were able to deduce certain internals of the hardware encryption engine. To our knowledge, this is the first attack against the bitstream encryption of a commercial FPGA reported in the open literature.

Posted on August 1, 2011 at 12:29 PM • View Comments

Cryptography and Wiretapping

Matt Blaze analyzes the 2010 U.S. Wiretap Report.

In 2000, government policy finally reversed course, acknowledging that encryption needed to become a critical part of security in modern networks, something that deserved to be encouraged, even if it might occasionally cause some trouble for law enforcement wiretappers. And since that time the transparent use of cryptography by everyday people (and criminals) has, in fact, exploded. Crypto software and algorithms, once categorized for arms control purposes as a “munition” alongside rocket launchers and nuclear triggers, can now be openly discussed, improved and incorporated into products and services without the end user even knowing that it’s there. Virtually every cellular telephone call is today encrypted and effectively impervious to unauthorized over-the-air eavesdropping. Web transactions, for everything from commerce to social networking, are now routinely encrypted end-to-end. (A few applications, particularly email and wireline telephony, remain stubbornly unencrypted, but they are increasingly the exception rather than the rule.)

So, with this increasing proliferation of eavesdrop-thwarting encryption built in to our infrastructure, we might expect law enforcement wiretap rooms to have become quiet, lonely places.

But not so fast: the latest wiretap report identifies a total of just six (out of 3194) cases in which encryption was encountered, and that prevented recovery of evidence a grand total of … (drumroll) … zero times. Not once. Previous wiretap reports have indicated similarly minuscule numbers.

I second Matt’s recommendation of Susan Landau’s book: Surveillance or Security: The Risks Posed by New Wiretapping Technologies (MIT Press, 2011). It’s an excellent discussion of the security and politics of wiretapping.

Posted on July 27, 2011 at 2:10 PM • View Comments

Telex Anti-Censorship System

This is really clever:

Many anticensorship systems work by making an encrypted connection (called a “tunnel”) from the user’s computer to a trusted proxy server located outside the censor’s network. This server relays requests to censored websites and returns the responses to the user over the encrypted tunnel. This approach leads to a cat-and-mouse game, where the censor attempts to discover and block the proxy servers. Users need to learn the address and login information for a proxy server somehow, and it’s very difficult to broadcast this information to a large number of users without the censor also learning it.

Telex turns this approach on its head to create what is essentially a proxy server without an IP address. In fact, users don’t need to know any secrets to connect. The user installs a Telex client app (perhaps by downloading it from an intermittently available website or by making a copy from a friend). When the user wants to visit a blacklisted site, the client establishes an encrypted HTTPS connection to a non-blacklisted web server outside the censor’s network, which could be a normal site that the user regularly visits. Since the connection looks normal, the censor allows it, but this connection is only a decoy.

The client secretly marks the connection as a Telex request by inserting a cryptographic tag into the headers. We construct this tag using a mechanism called public-key steganography. This means anyone can tag a connection using only publicly available information, but only the Telex service (using a private key) can recognize that a connection has been tagged.

As the connection travels over the Internet en route to the non-blacklisted site, it passes through routers at various ISPs in the core of the network. We envision that some of these ISPs would deploy equipment we call Telex stations. These devices hold a private key that lets them recognize tagged connections from Telex clients and decrypt these HTTPS connections. The stations then divert the connections to anti­censorship services, such as proxy servers or Tor entry points, which clients can use to access blocked sites. This creates an encrypted tunnel between the Telex user and Telex station at the ISP, redirecting connections to any site on the Internet.

EDITED TO ADD (8/1): Another article.

EDITED TO ADD (8/13): Another article.

Posted on July 19, 2011 at 9:59 AM • View Comments

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

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Sidebar photo of Bruce Schneier by Joe MacInnis.