Tracking Certificate Misissuance in the Wild

• Published in: 2018 IEEE Symposium on Security and Privacy (SP) pp. 785 - 798
• Main Authors: Kumar, Deepak, Zhengping Wang, Hyder, Matthew, Dickinson, Joseph, Beck, Gabrielle, Adrian, David, Mason, Joshua, Durumeric, Zakir, Halderman, J. Alex, Bailey, Michael
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.05.2018
• Subjects: Baseline Requirements; Browsers; Certificates; Compliance; Correlation; Cryptography; HTTPS; Organizations; PKI; RFC 5280; Standards organizations; TLS
• ISSN: 2375-1207
• DOI: 10.1109/SP.2018.00015

Certificate Authorities (CAs) regularly make mechanical errors when issuing certificates. To quantify these errors, we introduce ZLint, a certificate linter that codifies the policies set forth by the CA/Browser Forum Baseline Requirements and RFC 5280 that can be tested in isolation. We run ZLint on browser-trusted certificates in Censys and systematically analyze how well CAs construct certificates. We find that the number errors has drastically reduced since 2012. In 2017, only 0.02% of certificates have errors. However, this is largely due to a handful of large authorities that consistently issue correct certificates. There remains a long tail of small authorities that regularly issue non-conformant certificates. We further find that issuing certificates with errors is correlated with other types of mismanagement and for large authorities, browser action. Drawing on our analysis, we conclude with a discussion on how the community can best use lint data to identify authorities with worrisome organizational practices and ensure long-term health of the Web PKI.