Tracking Certificate Misissuance in the Wild

Abstract

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.Permission to freely reproduce all or part of this paper for noncommercial purposes is granted provided that copies bear this notice and the full citation on the first page. Reproduction for commercial purposes is strictly prohibited without the prior written consent of the Internet Society, the first-named author (for reproduction of an entire paper only), and the author's employer if the paper was prepared within the scope of employment.

The Rise of Certificate Transparency and Its Implications on the Internet Ecosystem

“…Our work confirms that corner-cases in CA software can cause invalid CT certificates. Most recently, the performance impact of CT on HTTPS [28] and the deployment of sub-par certificates sourced from CT logs [14,21] was measured. While the privacy implications and traceability of TLS certificates has been studied before [4,6,42], to the best of our knowledge, there is no detailed analysis on security and privacy aspects due to the rise of CT.…”

MERCAT: A Metric for the Evaluation and Reconsideration of Certificate Authority Trustworthiness

“…A different aspect directs to another interesting hypothesis concerning CAs and their individual compliance with prevalent regulations presented by Kumar et al [40]. The authors provide a comprehensive overview of CAs listing their respective certificates' error rates.…”

“…There are approaches to assess certificates by making use of information regarding the issuing CA such as results of a distributed reputation mechanism [20]; propositional logic and probability theory using so-called trustworthiness terms [61]; as well as certificate policies [67]. Kumar et al [40] monitored certificates issued by a wide range of CAs and analyzed their compliance with RFC 5280, the CA/Browser Forum's Baseline Requirements (BRs), and community best practices. Fadai et al [30] analyze the issuing institutions as well as the countries of origin of root certificates shipped with the currently most popular operating systems and browsers and correlate these findings against different indices indicating the CAs' origin states' constitutionality [3,31,55,66].…”

Let's Encrypt

“…To reduce the chances that bugs in Boulder could lead to misissuance or other problems, new versions are tested in a public staging environment prior to entering production. Boulder also applies ZLint [58] to perform automated conformance tests on every certificate, and any ZLint notices, warnings, or errors block issuance.…”