The SSL Landscape - A Thorough Analysis of the X.509 PKI Using Active and Passive Measurements

Ralph Holz, Lothar Braun, Nils Kammenhuber, Georg J. Carle

Research output: Chapter in Book/Report/Conference proceedingConference contributionAcademicpeer-review

122 Citations (Scopus)


The SSL and TLS infrastructure used in important protocols like HTTPs and IMAPs is built on an X.509 public-key infrastructure (PKI). X.509 certificates are thus used to authenticate services like online banking, shopping, e-mail, etc. However, it always has been felt that the certification processes of this PKI may lack in stringency, resulting in a deployment where many certificates do not meet the requirements of a secure PKI.

This paper presents a comprehensive analysis of X.509 certificates in the wild. To shed more light on the state of the deployed and actually used X.509 PKI, we obtained and evaluated data from many different sources. We conducted HTTPs scans of a large number of popular HTTPs servers over a 1.5-year time span, including scans from nine locations distributed over the globe. To compare certification properties of highly ranked hosts with the global picture, we included a third-party scan of the entire IPv4 space in our analyses. Furthermore, we monitored live SSL/TLS traffic on a 10Gbps uplink of a large research network. This allows us to compare the properties of the deployed PKI with the part of the PKI that is being actively accessed by users.

Our analysis reveals that the quality of certification lacks in stringency, due to a number of reasons among which incorrect certification chains or invalid certificate subjects give the most cause for concern. Similar concerns can be raised for the properties of certification chains and many self-signed certificates used in the deployed X.509 PKI. Our findings confirm what has long been believed -- namely that the X.509 PKI we often use in our everyday's lives is in a sorry state.
Original languageEnglish
Title of host publicationIMC '11
Subtitle of host publicationProceedings of the 2011 ACM SIGCOMM Internet Measurement Conference
EditorsPatrick Thiran, Walter Willinger
PublisherAssociation for Computing Machinery (ACM)
ISBN (Print)978-1-4503-1013-0
Publication statusPublished - 2011
Externally publishedYes


  • SSL,
  • TLS
  • X.509
  • Certificates
  • Public Key Infrastructure (KI)


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