Server has a weak ephemeral Diffie-Hellman public key message in browser
Problem
When navigating to your instance if JIRA, you receive a error message in your browser like the following:
"Server has a weak ephemeral Diffie-Hellman public key
ERR_SSL_WEAK_SERVER_EPHEMERAL_DH_KEY"
Cause
The message that you are getting is a broswer security feature that is designed to prevent users from accessing a site that has what it considers to be an "outdated security code" making it vulnerable the Logjam exploit.
Here is Chrome's explanation of the message: https://support.google.com/chrome/answer/6098869?p=dh_error&rd=1#DHkey
Resolution
This is an issue with the SSL certificate that is being used with your JIRA site, so you will need to consult with the vendor who provided the certificate.
For reference, you can learn more from this online guide: https://weakdh.org/sysadmin.html