Your only real option at this stage is look at hardware key storage such a a yubikey. This means that key material can't be removed but you can still auth to the backed up systems via the hardware key. This limits the attack to being started from the system with the hardware module, this only moves the problem about in your example as physical access and password resets can be used to backdoor the backup server fairly quickly.

It is quite easy to reset your user password in ubuntu if you have physical access to the machine. See https://help.ubuntu.com/community/LostPassword. This is why I wanted to encrypt the ssh keys. That way if someone resets the password they can't access the keys.

On Thursday, 28 July 2016, 14:23, Bowie Bailey <Bowie_Bailey AT BUC DOT com> wrote:

"if someone had physical access to backuppc server they could easily logon as backuppc user by resetting the password"

How would that work?  Unless you leave the backuppc user logged in, they would still need to either know the password or use some sort of hack to get access before being able to reset the password (such as rebooting with a live cd and accessing the OS partition directly).

Always protect physical access to important computers.  If someone has physical access to your server, all bets are off.  Also, if a user account has passwordless ssh keys giving root access to any of your systems, then you should make sure that the account has a strong password (at the least), or that the ssh keys that give access do require (strong) passwords.

Bowie

On 7/28/2016 9:01 AM, lanceh1412-business AT yahoo.co DOT uk wrote:

I hadn't really thought about the danger from a restore. I guess that would require quite a bit of technical knowledge of backuppc to engineer an attack on a server? It would require significantly less knowledge to steal the ssh keys on an unencrypted server and then have root access. 

On Thursday, 28 July 2016, 13:11, Carl Wilhelm Soderstrom <chrome AT real-time DOT com> wrote:

On 07/28 10:53 , lanceh1412-business AT yahoo.co DOT uk wrote:

> Just trying to harden security. My concern is if someone had physical access to backuppc server they could easily logon as backuppc user by resetting the password and therefore gain access to the ssh keys. Now I see it is possible to put the ssh keys in an encrypted private directory (See EncryptedPrivateDirectory - Community Help Wiki). This would mean that even if someone could reset the password and logon as backuppc they wouldn't have access to the keys.
> Has anyone done this or would recommend this way or got any other suggestions?

My logic for my setup is:
if someone has access to the BackupPC server, they have all the data on all
the computers being backed up. At that point, the risk is whether they could
modify data on the live server.

To avoid that risk, I don't allow the BackupPC server write access to the
machines being backed up, only read access. The restores aren't really much
more inconvenient (I tend to use tar+netcat for restores on Linux boxen, and
zipfile downloads on Windows boxen), and I feel like I have more confidence
that I'm not going to accidentally clobber the wrong data.

--
Carl Soderstrom
Systems Administrator
Real-Time Enterprises
www.real-time.com

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