The march of standards continues unabated. Legacy TLS protocols 1.0 and 1.1 have varying weaknesses that could lead to a false sense of security.
In June 2018, in an effort to raise security and comply with modern standards, the insecure TLS 1.0 & 1.1 protocols will no longer be supported for SSL connections to Maven Central. This should only affect users of Java 6 that are also using https to access Central, which by our metrics is less than .2% of users.
At the same time, this conversion will allow Central to support HTTP/2 with potential performance gains for modern http clients.
The details about why, when and what you need to do are documented at the link below. As questions come up, we will continue to update this FAQ.
If there is specific information required for non-maven build systems, please send it along and we will include that as well.
EDIT: Link updated: https://central.sonatype.org/faq/tls-info/