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Adrian Perrig: Improve SSL/TLS Security Through Education and Technology

Carnegie Mellon University's CyLab designs security to improve all aspects of society.

Despite much recent progress in the area of user-centric design of secure systems, user error continues to cause a large number of security vulnerabilities in current systems. Both user education and technology can help to improve this situation.

At CyLab at Carnegie Mellon University, our goal is to improve security in all aspects of society. First, we developed educational programs to train students in security. Second, CyLab researchers also engage in several efforts to design systems that continue to remain secure despite human errors, as well as develop technologies that provide improved situational awareness to the user.

Using the Secure Socket Layer (SSL) / Transport Layer Security (TLS) protocols for secure https Web connections as a case study, we will first describe how education has helped improve Web security, followed by a description of the Perspectives project, which provides additional information for users to make better security decisions. To provide some background for our discussion, we briefly revisit some SSL/TLS security-relevant fundamentals.

SSL/TLS is a protocol to provide communication secrecy and authenticity, and is invoked whenever we access an https-based Web page. Although SSL/TLS is a well-designed protocol, it still needs to face the complexities and realities of our computing environment, which result in numerous opportunities for user error and the following vulnerabilities.

Probably the most fundamental threat to SSL/TLS security is a so-called man-in-the-middle (MitM) attack, where an adversary interposes in a connection between a client and a server to eavesdrop on communication or inject malicious data. Such MitM attacks can be mounted by any entity handling network packets, and is usually mounted in wireless networks in public environments, e.g., in coffee shops, airports, conferences, etc. The SSL/TLS protocol is designed to protect against man-in-the-middle attacks.

Unfortunately, many real-world issues still enable adversaries to mount attacks. For example, cryptographic vulnerabilities can enable attackers to mount MitM attacks, for example by exploiting the collision resistance of the MD5 hash function--researchers recently demonstrated a successful attack where they were able to obtain a bogus certificate that enabled creation of arbitrary additional certificates trusted by current browsers. Browser or OS vulnerabilities enable adversaries to inject bogus certificates into the trusted set of browser root certificates. Users can be tricked into visiting a bogus URL or to install bogus root certificates. CAs can be tricked into issuing certificates to the wrong entities. These are just a few examples that would enable an adversary to mount a successful man-in-the-middle attack. Given that we cannot redesign the current legacy computing environment in the near term, we need rely on education and technology to enhance the current state of SSL/TLS security.

Over the past seven years, I have been teaching more than 100 students each year about the various issues with SSL/TLS. (The student composition was mostly Master's-degree students enrolled in CMU's security MS programs.) In several instances, the lessons learned in class fell on fertile ground: the students immediately assessed the security of their banks' websites and informed their banks to report cases of inadequate security. In numerous instances, the banks listened to the students' feedback and promptly improved security. In some cases, it was as simple as fixing a typo by adding the critical "s" to complete the URL to "https" for the login page. In more difficult cases, students needed to convince the banks' security administrators that Javascript-based encryption loaded from a non-https page can be easily removed by a MitM attacker. In summary, by educating a critical mass of students that further disseminate security knowledge can result in real improved security for everyone.

Together with student education, technology that provides the user with additional information for improved security decision making can also enhance security. To improve security for https sites with self-signed certificates, as well as detect numerous attacks on https sites using bogus certificates, Dan Wendlandt, Dave Andersen and I designed and built Perspectives [] , a Firefox plug-in that connects to notary servers to assist in validating https credentials. Perspectives informs the user for how long an https credential has been observed for a given server []. This simple user feedback enables users to make better security decisions, in fact, I gained more confidence in my personal Web browsing by knowing that the https credentials of the servers I visit had been in use for a while--which assures me of the absence of a variety of attacks.

In summary, by leveraging education and technology for improved user information, we can increase the security of our current systems in the short term. To achieve a stronger level of security in the long term, however, redesigning more robust systems seems to be necessary.


TITLE Professor electrical and computer engineering, computer science, and engineering and public policy; technical director, CyLab
COMPANY Carnegie Mellon University
INDUSTRY Education

  • Research is on the cutting edge of network security and safe usability features
  • Developed Phoolproof Phishing Prevention, a software tool that relies on trusted individual devices to perform mutual authentication
  • Also helped build Seeing-Is-Believing, a version of PKI between mobile devices that eliminates the need for central key authorities through visual recognition of 2D barcodes
  • Oversees the development of Flicker, which leverages features in AMD and Intel hardware to limit execution of application specific code to only isolated areas of a machine
  • Collaborated on Perspectives, a Firefox plug-in that cuts down the risk of users falling victim to man-in-the-middle browsing attacks.

Adrian Perrig's students and research teams aren't tasked with solving today's pressing security threats, instead, they're working on attacking tomorrow's threats by designing systems that cut down on user error. His invaluable work is the foundation for the security tools and practices of the next decade.

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