Unattended remote ssh login
I have numerous remote client machines that perform unattended rsync backups using a private/public key pair. What is the best way to protect the private key? If I use a passphrase then ssh will ask for it everytime it executes from a cron job. This client machine is only on every 20 minutes for about a minute only. Can I respond to the ssh passphrase request using a compiled c program. I know the c program can be reverse engineered but expect this would be too much of a hassle. Any ideas would be greatly appreciated.