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).
~/.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/id_rsa.pub Contains the public key for authentication. These files are not sensitive and can (but need not) be readable by anyone.