Cryptographic Failures in Practice

Zakir Durumeric


Despite advances in cryptography, there remains a significant gap between developed algorithms and how systems are protected in practice. In this talk, I will discuss two studies in which Internet-wide measurement has uncovered catastrophic cryptographic failures in practice. In the first, we investigate the Diffie-Hellman key exchange, finding it far less secure than widely believed. I'll present Logjam, a novel flaw in TLS that lets a man-in-the-middle downgrade connections to “export-grade” Diffie-Hellman, and then go on to consider how a small number of fixed or standardized groups may allow for passive eavesdropping by nation-state attackers.

Next, I'll discuss our recent analysis of mail delivery security. We find that the top mail providers all proactively encrypt and authenticate messages. However, these best practices have yet to reach widespread adoption and only one third of top domains successfully configure encryption, and only 1% support mail authentication. This patchwork has led to an ecosystem where servers favor failing open to allow gradual deployment. However, we find that downgrade attacks are commonplace in the real world and highlight seven countries where more than 20% of inbound Gmail messages arrive in cleartext due to network attackers.


Zakir Durumeric is a Ph.D. Candidate in Computer Science and Engineering at the University of Michigan and the 2014 Google Ph.D. Fellow in Computer Security. His research focuses on network security, particularly how global network measurement can improve the security of heterogeneous distributed systems. Zakir is widely known for creating ZMap—the Internet-wide network scanner capable of scanning the entire public IPv4 address space in minutes—and Censys—the search engine that allows researchers to analyze the devices that compose the public Internet. His work has been awarded numerous distinctions, including the IRTF Applied Networking Research Prize and best paper awards from USENIX Security, ACM Conference on Computer and Communications Security, and ACM Internet Measurement Conference. He was named one of this year's MIT Technology Review’s 35 Innovators under 35.

Time and Place

Tuesday, March 8, 4:15pm
Gates 463