brew update permission error yosemite

Question

When I run brew update I get the following error message

$ brew update
Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
Error: Failure while executing: git pull -q origin refs/heads/master:refs/remotes/origin/master

I am on OS X Yosemite.

Answer 1

GitHub isn't able to authenticate you. So, either you aren't setup with an SSH key, because you haven't set one up on your machine, or your key isn't associated with your GitHub account.