SHA1 certificates for secure SSL/TLS communications are deprecated due to known computational vulnerabilities. To ensure secure communications, a forced deprecation sounds reasonable (i.e. refuse to connect to these). That has the side effect that it will lock out many users who are unable to use stronger hashes such as SHA256. However, if a fallback to SHA1 is provided (as Facebook is proposing), everyone will be vulnerable to SHA1 downgrade man-in-the-middle attacks.
What to do?
(Score: 2, Insightful) by Anonymous Coward on Friday December 11 2015, @10:26PM
> Really, secure connections should only be needed for truly sensitive data like banking.
No, secure connections should be used for ALL data. Otherwise it calls attention to itself and makes it easy for attackers to focus on the most valuable network traffic.
This is a case of "a rising tide lifts all boats."