In this paper, we analyze the evolution of Certificate Transparency (CT) over time and explore the implications of exposing certificate DNS names from the perspective of security and privacy. We find that certificates in CT logs have seen exponential growth. Website support for CT has also constantly increased, with now 33 of established connections supporting CT. With the increasing deployment of CT, there are also concerns of information leakage due to all certificates being visible in CT logs. To understand this threat, we introduce a CT honeypot and show that data from CT logs is being used to identify targets for scanning campaigns only minutes after certificate issuance. We present and evaluate a methodology to learn and validate new subdomains from the vast number of domains extracted from CT logged certificates.
Although standardization of CT began mid of 2012, it only recently raised interest in the measurement community. Before CT was mandatory in Chrome, focus was on active scans to quantify coverage of various certificate sources @cite_16 and to describe basic properties of logs and certificates in the CT ecosystem @cite_6 . Then, CT as part of various HTTPS security extensions was analyzed @cite_15 . Our work confirms that corner-cases in CA software can cause invalid CT certificates. Most recently, the performance impact of CT on HTTPS @cite_25 and the deployment of sub-par certificates sourced from CT logs @cite_38 @cite_29 was measured. While the privacy implications and traceability of TLS certificates has been studied before @cite_23 @cite_3 @cite_18 , to the best of our knowledge, there is no detailed analysis on security and privacy aspects due to the rise of CT.
@cite_38 @cite_18 @cite_29 @cite_6 @cite_3 @cite_23 @cite_15 @cite_16 @cite_25
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Many of today’s web-based services rely heavily on secure end-to-end connections. The “trust” that these services require builds upon TLS SSL. Unfortunately, TLS SSL is highly vulnerable to compromised Certificate Authorities (CAs) and the certificates they generate. Certificate Transparency (CT) provides a way to monitor and audit certificates and certificate chains, to help improve the overall network security. Using an open standard, anybody can setup CT logs, monitors, and auditors. CT is already used by Google’s Chrome browser for validation of Extended Validation (EV) certificates, Mozilla is drafting their own CT policies to be enforced, and public CT logs have proven valuable in identifying rogue certificates. In this paper we present the first large-scale characterization of the CT landscape. Our characterization uses both active and passive measurements and highlights similarities and differences in public CT logs, their usage, and the certificates they include. We also provide insights into how the certificates in these logs relate to the certificates and keys observed in regular web traffic. Certificate Transparency (CT) was developed to mitigate shortcomings in the TLS SSL landscape and to assess the trustworthiness of Certificate Authorities (CAs) and the certificates they create. With CT, certificates should be logged in public, audible, append-only CT logs and servers should provide clients (browsers) evidence, in the form of Signed Certificate Timestamps (SCTs), that the certificates that they present have been logged in credible CT logs. These SCTs can be delivered using three different methods: (i) X.509v3 extension, (ii) TLS extension, and (iii) OSCP stapling. In this paper, we develop a client-side measurement tool that implements all three methods and use the tool to analyze the SCT adoption among the one-million most popular web domains. Using two snapshots (from May and Oct. 2017), we answer a wide range of questions related to the delivery choices made by different domains, identify differences in the certificates used by these domains, the CT logs they use, and characterize the overheads and potential performance impact of the SCT delivery methods. By highlighting some of the tradeoffs between the methods and differences in the websites selecting them, we provide insights into the current SCT adoption status and differences in how domains have gone upon adopting this new technology. The HTTPS certificate ecosystem has been of great interest to the measurement and security communities. Without any ground truth, researchers have attempted to study this PKI from a variety of fragmented perspectives, including passively monitored networks, scans of the popular domains or the IPv4 address space, search engines such as Censys, and Certificate Transparency (CT) logs. In this work, we comparatively analyze all these perspectives. We find that aggregated CT logs and Censys snapshots have many properties that complement each other, and that together they encompass over 99 of all certificates found by any of these techniques. However, they still miss 1.5 of certificates observed in a crawl of all domains in .com, .net, and .org. We go on to illustrate how this combined perspective affects results from previous studies. In light of these findings, we have worked with the operators of Censys to incorporate CT log data into its results going forward, and we recommend that future HTTPS measurement adopt this new vantage. Driven by CA compromises and the risk of man-in-the-middle attacks, new security features have been added to TLS, HTTPS, and the web PKI over the past five years. These include Certificate Transparency (CT), for making the CA system auditable; HSTS and HPKP headers, to harden the HTTPS posture of a domain; the DNS-based extensions CAA and TLSA, for control over certificate issuance and pinning; and SCSV, for protocol downgrade protection. This paper presents the first large scale investigation of these improvements to the HTTPS ecosystem, explicitly accounting for their combined usage. In addition to collecting passive measurements at the Internet uplinks of large University networks on three continents, we perform the largest domain-based active Internet scan to date, covering 193M domains. Furthermore, we track the long-term deployment history of new TLS security features by leveraging passive observations dating back to 2012. We find that while deployment of new security features has picked up in general, only SCSV (49M domains) and CT (7M domains) have gained enough momentum to improve the overall security of HTTPS. Features with higher complexity, such as HPKP, are deployed scarcely and often incorrectly. Our empirical findings are placed in the context of risk, deployment effort, and benefit of these new technologies, and actionable steps for improvement are proposed. We cross-correlate use of features and find some techniques with significant correlation in deployment. We support reproducible research and publicly release data and code.