The Debian distribution is experimenting with disabling older versions of Transport Layer Security (TLS) which are generally considered to be no longer secure. TLS allows networked applications to transmit information across the Internet securely and is an important technology for applications such as web browsers and e-mail clients. On Debian, TLS is implemented in the OpenSSL library and the latest version of OpenSSL in Debian's Unstable branch disables older, vulnerabele versions of TLS while keeping more modern versions. There is some concerns that older or unmaintained applications may not work when older versions of TLS are disabled: "This will likely break certain things that for whatever reason still don't support TLS 1.2. I strongly suggest that if it's not supported that you add support for it, or get the other side to add support for it. OpenSSL made a release five years ago that supported TLS 1.2. The current support of the server side seems to be around 90%. I hope that by the time Buster releases the support for TLS 1.2 will be high enough that I don't need to enable them again." Information on this change can be found in a Debian mailing list post.