Putty - Permissions 0644 for key are too open

Ошибка при подключении через приватный ключ:

# ssh -i 1.key root@server_ip
Permissions 0644 for '1.key' are too open.
It is required that your private key files are NOT accessible by others.
This private key will be ignored.
Load key "1.key": bad permissions
root@server_ip: Permission denied (publickey).

Решение - поставить права 400 на приватный ключ:

# chmod 400 1.key

и зайти заново по ssh.