Linux is very sensitive to permissions settings.
From your home directory, you should have the following:
user@server:~$ ls -alF .ssh/
drwxr-xr-x 2 user user 4096 Oct 30 04:39 ./
drwxr-x--- 5 user user 4096 Nov 5 15:50 ../
-rw------- 1 user user 1457 Oct 30 00:55 authorized_keys
