For SSH to work properly the permissions must be set as follows, according to this:
- .ssh directory: 700 (drwx------)
- public key (.pub file): 644 (-rw-r--r--)
- private key (id_rsa): 600 (-rw-------)
- the HOME should not be writeable by the group or others: at most 755 (drwxr-xr-x)