  TLS 1.3 marks a significant departure from previous versions of the Transport
Layer Security protocol (TLS). The new version offers a simplified protocol
flow, more secure cryptographic primitives, and new features to improve
performance, among other things. In this paper, we conduct the first study of
TLS 1.3 deployment and use since its standardization by the IETF. We use active
scans to measure deployment across more than 275M domains, including nearly 90M
country-code top-level domains. We establish and investigate the critical
contribution that hosting services and CDNs make to the fast, initial uptake of
the protocol. We use passive monitoring at two positions on the globe to
determine the degree to which users profit from the new protocol and establish
the usage of its new features. Finally, we exploit data from a widely deployed
measurement app in the Android ecosystem to analyze the use of TLS 1.3 in
mobile networks and in mobile browsers. Our study shows that TLS 1.3 enjoys
enormous support even in its early days, unprecedented for any TLS version.
However, this is strongly related to very few global players pushing it into
the market and sustaining its growth.
