[CentOS] ultrasecure sshd server

>> If you want 2 factor authentication, you can add yubikeys. They are 
>> little
>> usb dongle that provides one-time-password. And the server-side for those 
>> is
>> open-source if you don't want to use their authentication servers. And 
>> they
>> are relatively cheap.
>>
>> We use these here on our border servers to increase security.
>
> is this easy to ingrate with openssh server on centos 5.x ?

There is 2 rpm in epel (libyubikey and pam_yubico) that make it pretty easy 
to integrate into openssh (via pam).