macOS Sierra: Why do I have to enter the password for my private key? I recently upgraded my computer to macOS Sierra. Everything went fine, but somewhere along the way something got changed (probably something I did) and now every time I try to ssh into another machine the terminal prompts me to enter my password. If I type the password and enter it the ssh session works as normal. But why do I have to enter my password at all? What can I do to fix this? 

Side note: I have tried changing the file permissions to no avail. They are currently 644 like the public key.
You need add your private key to ssh agent again. I faced same problem after Sierra update.

Here is a guide to add your key.