Entries Tagged "certificates"

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Man-in-the-Middle Attacks Against SSL

Says Matt Blaze:

A decade ago, I observed that commercial certificate authorities protect you from anyone from whom they are unwilling to take money. That turns out to be wrong; they don’t even do that much.

Scary research by Christopher Soghoian and Sid Stamm:

Abstract: This paper introduces a new attack, the compelled certificate creation attack, in which government agencies compel a certificate authority to issue false SSL certificates that are then used by intelligence agencies to covertly intercept and hijack individuals’ secure Web-based communications. We reveal alarming evidence that suggests that this attack is in active use. Finally, we introduce a lightweight browser add-on that detects and thwarts such attacks.

Even more scary, Soghoian and Stamm found that hardware to perform this attack is being produced and sold:

At a recent wiretapping convention, however, security researcher Chris Soghoian discovered that a small company was marketing internet spying boxes to the feds. The boxes were designed to intercept those communications—without breaking the encryption—by using forged security certificates, instead of the real ones that websites use to verify secure connections. To use the appliance, the government would need to acquire a forged certificate from any one of more than 100 trusted Certificate Authorities.


The company in question is known as Packet Forensics…. According to the flyer: “Users have the ability to import a copy of any legitimate key they obtain (potentially by court order) or they can generate ‘look-alike’ keys designed to give the subject a false sense of confidence in its authenticity.” The product is recommended to government investigators, saying “IP communication dictates the need to examine encrypted traffic at will.” And, “Your investigative staff will collect its best evidence while users are lulled into a false sense of security afforded by web, e-mail or VOIP encryption.”

Matt Blaze has the best analysis. Read his whole commentary; this is just the ending:

It’s worth pointing out that, from the perspective of a law enforcement or intelligence agency, this sort of surveillance is far from ideal. A central requirement for most government wiretapping (mandated, for example, in the CALEA standards for telephone interception) is that surveillance be undetectable. But issuing a bogus web certificate carries with it the risk of detection by the target, either in real-time or after the fact, especially if it’s for a web site already visited. Although current browsers don’t ordinarily detect unusual or suspiciously changed certificates, there’s no fundamental reason they couldn’t (and the Soghoian/Stamm paper proposes a Firefox plugin to do just that). In any case, there’s no reliable way for the wiretapper to know in advance whether the target will be alerted by a browser that scrutinizes new certificates.

Also, it’s not clear how web interception would be particularly useful for many of the most common law enforcement investigative scenarios. If a suspect is buying books or making hotel reservations online, it’s usually a simple (and legally relatively uncomplicated) matter to just ask the vendor about the transaction, no wiretapping required. This suggests that these products may be aimed less at law enforcement than at national intelligence agencies, who might be reluctant (or unable) to obtain overt cooperation from web site operators (who may be located abroad).

Posted on April 12, 2010 at 1:32 PMView Comments

Too Many Security Warnings Results in Complacency

Research that proves what we already knew:

Crying Wolf: An Empirical Study of SSL Warning Effectiveness

Abstract. Web users are shown an invalid certificate warning when their browser cannot validate the identity of the websites they are visiting. While these warnings often appear in benign situations, they can also signal a man-in-the-middle attack. We conducted a survey of over 400 Internet users to examine their reactions to and understanding of current SSL warnings. We then designed two new warnings using warnings science principles and lessons learned from the survey. We evaluated warnings used in three popular web browsers and our two warnings in a 100-participant, between-subjects laboratory study. Our warnings performed significantly better than existing warnings, but far too many participants exhibited dangerous behavior in all warning conditions. Our results suggest that, while warnings can be improved, a better approach may be to minimize the use of SSL warnings altogether by blocking users from making unsafe connections and eliminating warnings in benign

Posted on August 4, 2009 at 10:01 AMView Comments

Forging SSL Certificates

We already knew that MD5 is a broken hash function. Now researchers have successfully forged MD5-signed certificates:

Molnar, Appelbaum, and Sotirov joined forces with the European MD5 research team in mid-2008, along with Swiss cryptographer Dag Arne Osvik. They realized that the co-construction technique could be used to simultaneously generate one normal SSL certificate and one forged certificate, which could be used to sign and vouch for any other. They purchased a signature for the legitimate certificate from an established company that was still using MD5 for signing, and then applied the legitimate signature to the forged certificate. Because the legitimate and forged certificates had the same MD5 value, the legitimate signature also marked the forged one as acceptable.

Lots and lots more articles, and the research.

This isn’t a big deal. The research is great; it’s good work, and I always like to see cryptanalytic attacks used to break real-world security systems. Making that jump is often much harder than cryptographers think.

But SSL doesn’t provide much in the way of security, so breaking it doesn’t harm security very much. Pretty much no one ever verifies SSL certificates, so there’s not much attack value in being able to forge them. And even more generally, the major risks to data on the Internet are at the endpoints—Trojans and rootkits on users’ computers, attacks against databases and servers, etc—and not in the network.

I’m not losing a whole lot of sleep because of these attacks. But—come on, people—no one should be using MD5 anymore.

EDITED TO ADD (12/31): While it is true that browsers do some SSL certificate verification, when they find an invalid certificate they display a warning dialog box which everyone—me included—ignores. There are simply too many valid sites out there with bad certificates for that warning to mean anything. This is far too true:

If you’re like me and every other user on the planet, you don’t give a shit when an SSL certificate doesn’t validate. Unfortunately, commons-httpclient was written by some pedantic fucknozzles who have never tried to fetch real-world webpages.

Posted on December 31, 2008 at 1:39 PMView Comments

How to Clone and Modify E-Passports

The Hackers Choice has released a tool allowing people to clone and modify electronic passports.

The problem is self-signed certificates.

A CA is not a great solution:

Using a Certification Authority (CA) could solve the attack but at the same time introduces a new set of attack vectors:

  1. The CA becomes a single point of failure. It becomes the juicy/high-value target for the attacker. Single point of failures are not good. Attractive targets are not good.

    Any person with access to the CA key can undetectably fake passports. Direct attacks, virus, misplacing the key by accident (the UK government is good at this!) or bribery are just a few ways of getting the CA key.

  2. The single CA would need to be trusted by all governments. This is not practical as this means that passports would no longer be a national matter.
  3. Multiple CA’s would not work either. Any country could use its own CA to create a valid passport of any other country. Read this sentence again: Country A can create a passport data set of Country B and sign it with Country A’s CA key. The terminal will validate and display the information as data from Country B.This option also multiplies the number of ‘juicy’ targets. It makes it also more likely for a CA key to leak.

    Revocation lists for certificates only work when a leak/loss is detected. In most cases it will not be detected.

So what’s the solution? We know that humans are good at Border Control. In the end they protected us well for the last 120 years. We also know that humans are good at pattern matching and image recognition. Humans also do an excellent job ‘assessing’ the person and not just the passport. Take the human part away and passport security falls apart.

EDITED TO ADD (10/13): More information.

Posted on September 30, 2008 at 12:24 PMView Comments

Sidebar photo of Bruce Schneier by Joe MacInnis.