Keys need to be only readable by you:
chmod 400 ~/.ssh/id_rsa
If Keys need to be read-writable by you:
chmod 600 ~/.ssh/id_rsa
600 appears to be fine as well (in fact better in most cases, because you don’t need to change file permissions later to edit it).
The relevant portion from the manpage (man ssh)
~/.ssh/id_rsa
Contains the private key for authentication. These files contain sensitive
data and should be readable by the user but not
accessible by others (read/write/execute). ssh will simply ignore a private
key file if it is
accessible by others. It is possible to specify a
passphrase when generating the key which will be used to encrypt the sensitive
part of this file using 3DES.
~/.ssh/identity.pub
~/.ssh/id_dsa.pub
~/.ssh/id_ecdsa.pub
~/.ssh/id_rsa.pub
Contains the public key for authentication. These files are not sensitive and
can (but need not) be readable by anyone.
