You can achieve this using OpenSSL. (Mac OSX includes OpenSSL within Terminal.app)
SHA is a popular hashing algorithm used by the majority of SSL certificates. As computing power has increased the feasibility of breaking the SHA1 hash has increased.
This usually means the implementation of SSL on your server is not correct. The error is usually caused by a server side problem which the server administrator will need to investigate.
A warning is displayed in the Chrome console window regarding your certificate
Some hosting systems require the Private key to be in RSA format rather than PEM. You can easily convert these files using OpenSSL.