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Old 04-15-2008, 09:48 AM
Fajar Priyanto
 
Default SSH Question relating to Public and Private Keys

On Tuesday 15 April 2008 16:13:55 William L. Maltby wrote:
> How sensitive is the data and how critical are the functions that that
> could be disrupted? What is the scope of exposure to intrusion from
> outside the organization (LAN, firewalls, in place, etc.).

For example rsync functions.
It won't work automatically anymore in cron if we use passphrase.

--
Fajar Priyanto | Reg'd Linux User #327841 | Linux tutorial
http://linux2.arinet.org
16:48:28 up 8:02, 2.6.22-14-generic GNU/Linux
Let's use OpenOffice. http://www.openoffice.org
The real challenge of teaching is getting your students motivated to learn.
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Old 04-15-2008, 12:08 PM
Peter Kjellstrom
 
Default SSH Question relating to Public and Private Keys

On Tuesday 15 April 2008, Fajar Priyanto wrote:
> On Tuesday 15 April 2008 16:13:55 William L. Maltby wrote:
> > How sensitive is the data and how critical are the functions that that
> > could be disrupted? What is the scope of exposure to intrusion from
> > outside the organization (LAN, firewalls, in place, etc.).
>
> For example rsync functions.
> It won't work automatically anymore in cron if we use passphrase.

Then please do use a restricted key. More specifically, add the key to the
authorized_keys with restrictions (see man pages)

/Peter
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Old 04-15-2008, 12:12 PM
Peter Kjellstrom
 
Default SSH Question relating to Public and Private Keys

On Tuesday 15 April 2008, Clint Dilks wrote:
> 1. Currently all of the key pairs we are using have empty passphrases is
> it worth the effort of changing this and setting up ssh-agent compared
> to what you gain in security by doing this ?

To get a clear idea of what keys with no passphrases are like consider the
idea that users put their regular password in /home/$USER/my_passwd.txt

We try our very best to stop any use of key-pairs without passphrase. All
modern distros have ssh-agents. Using it is trivial, not using it is lazy.
For extra security use "ssh-add -c" and you'll know when your agent is
actually signing stuff.

/Peter
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Old 04-15-2008, 03:24 PM
Ingemar Nilsson
 
Default SSH Question relating to Public and Private Keys

Fajar Priyanto wrote:

On Tuesday 15 April 2008 16:13:55 William L. Maltby wrote:

How sensitive is the data and how critical are the functions that that
could be disrupted? What is the scope of exposure to intrusion from
outside the organization (LAN, firewalls, in place, etc.).


For example rsync functions.
It won't work automatically anymore in cron if we use passphrase.


Do you know what command rsync will run on the remote host? If you do,
you can create a key pair without a passphrase and add the public key to
the remote host, along with a forced command. This will allow the client
with the corresponding private key to run this command only.


Regards
Ingemar
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Old 04-15-2008, 10:53 PM
Clint Dilks
 
Default SSH Question relating to Public and Private Keys

Clint Dilks wrote:

Hi People,

The Linux Environment I am responsible for is using ssh key pairs to
allow access to a number or accounts on a number Linux Servers. I
currently have the opportunity to re-design some of this. So I would
like to tap into peoples experiences to see what might be some good
changes to make. Specifically I have a couple of questions


1. Currently all of the key pairs we are using have empty passphrases
is it worth the effort of changing this and setting up ssh-agent
compared to what you gain in security by doing this ?


2. At this stage I am going to use RSA Keys of the default size, is
this generally the best approach?



Thanks for any thoughts, and have a nice day
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Hi Again people, thank you for all the responses. You have definitely
given me something to think about. Much appreciated


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Old 04-17-2008, 12:15 AM
"Brian Mathis"
 
Default SSH Question relating to Public and Private Keys

On Tue, Apr 15, 2008 at 8:12 AM, Peter Kjellstrom <cap@nsc.liu.se> wrote:
> On Tuesday 15 April 2008, Clint Dilks wrote:
> > 1. Currently all of the key pairs we are using have empty passphrases is
> > it worth the effort of changing this and setting up ssh-agent compared
> > to what you gain in security by doing this ?
>
> To get a clear idea of what keys with no passphrases are like consider the
> idea that users put their regular password in /home/$USER/my_passwd.txt
>
> We try our very best to stop any use of key-pairs without passphrase. All
> modern distros have ssh-agents. Using it is trivial, not using it is lazy.
> For extra security use "ssh-add -c" and you'll know when your agent is
> actually signing stuff.
>
> /Peter
>

This is a HUGE step backwards in security! Now when your system in
compromised, the attacker will be able to get into ALL of the systems
that user has used that password on. Face it, users often use the
same password everywhere. This is really a bad, bad idea.

With password-less SSH keys, at least they only gain access to the
systems with the corresponding key.

Using an ssh-agent is often not feasible for system-level functions
that need to SSH. Who's going to be there at 2AM to type in the
passphrase when the system reboots? If you script it, then you just
put the plaintext password in a script file again, and now have the
same problem.

Remember, the old way of doing this was with rsh and .rhosts files,
and those were a problem because DNS could more easily be compromised,
and the system tricked into letting you in. SSH keys are meant to get
around THAT problem. Otherwise, all the secret keyfiles are protected
using restrictive permissions, which is what you have to rely on for
this security.
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Old 04-17-2008, 12:16 AM
"Brian Mathis"
 
Default SSH Question relating to Public and Private Keys

On Wed, Apr 16, 2008 at 8:15 PM, Brian Mathis <brian.mathis@gmail.com> wrote:
>
> On Tue, Apr 15, 2008 at 8:12 AM, Peter Kjellstrom <cap@nsc.liu.se> wrote:
> > On Tuesday 15 April 2008, Clint Dilks wrote:
> > > 1. Currently all of the key pairs we are using have empty passphrases is
> > > it worth the effort of changing this and setting up ssh-agent compared
> > > to what you gain in security by doing this ?
> >
> > To get a clear idea of what keys with no passphrases are like consider the
> > idea that users put their regular password in /home/$USER/my_passwd.txt
> >
> > /Peter
> >
>
> This is a HUGE step backwards in security! Now when your system in
> compromised, the attacker will be able to get into ALL of the systems
> that user has used that password on. Face it, users often use the
> same password everywhere. This is really a bad, bad idea.

OK, I misread this part Sorry.
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Old 04-17-2008, 03:28 AM
"Andreas Pedersen"
 
Default SSH Question relating to Public and Private Keys

On Tue, Apr 15, 2008 at 11:48 AM, Fajar Priyanto <fajarpri@cbn.net.id> wrote:
> On Tuesday 15 April 2008 16:13:55 William L. Maltby wrote:
> > How sensitive is the data and how critical are the functions that that
> > could be disrupted? What is the scope of exposure to intrusion from
> > outside the organization (LAN, firewalls, in place, etc.).
>
> For example rsync functions.
> It won't work automatically anymore in cron if we use passphrase.

Use restricted shells if your doing cronjobs with rsync, You sould
take a look at rssh http://dragontoe.org/rssh/.

Andreas Pedersen

>
> --
> Fajar Priyanto | Reg'd Linux User #327841 | Linux tutorial
> http://linux2.arinet.org
> 16:48:28 up 8:02, 2.6.22-14-generic GNU/Linux
> Let's use OpenOffice. http://www.openoffice.org
> The real challenge of teaching is getting your students motivated to learn.
>
> _______________________________________________
> CentOS mailing list
> CentOS@centos.org
> http://lists.centos.org/mailman/listinfo/centos
>
>
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Old 04-17-2008, 12:56 PM
Peter Kjellstrom
 
Default SSH Question relating to Public and Private Keys

On Thursday 17 April 2008, Brian Mathis wrote:
> On Tue, Apr 15, 2008 at 8:12 AM, Peter Kjellstrom <cap@nsc.liu.se> wrote:
> > On Tuesday 15 April 2008, Clint Dilks wrote:
> > > 1. Currently all of the key pairs we are using have empty passphrases
> > > is it worth the effort of changing this and setting up ssh-agent
> > > compared to what you gain in security by doing this ?
> >
> > To get a clear idea of what keys with no passphrases are like consider
> > the idea that users put their regular password in
> > /home/$USER/my_passwd.txt
> >
> > We try our very best to stop any use of key-pairs without passphrase.
> > All modern distros have ssh-agents. Using it is trivial, not using it is
> > lazy. For extra security use "ssh-add -c" and you'll know when your agent
> > is actually signing stuff.
> >
> > /Peter

First, I'm not sure what point (if any) you're trying to make. Did you agree
with me, the OP, neither?

> This is a HUGE step backwards in security!

What is? Not writing comments inline where they belong is confusing.

> Now when your system in
> compromised, the attacker will be able to get into ALL of the systems
> that user has used that password on. Face it, users often use the
> same password everywhere. This is really a bad, bad idea.

Exactly, very very bad, that was my point.

> With password-less SSH keys, at least they only gain access to the
> systems with the corresponding key.

Just as bad, why would users re-user ssh-keys more often than passwords?

> Using an ssh-agent is often not feasible for system-level functions
> that need to SSH.

Wow, context switch. First we were talking users, now system automation tasks.
Quite clearly very different tasks with very different security aspects and
trade-offs.

IMO this is best done with either a suitable restriction in the
authorized_keys file (effectively limiting what you can do with the
corresponding private key) or a restricted shell setup (see other post in
thread).

> Who's going to be there at 2AM to type in the
> passphrase when the system reboots? If you script it, then you just
> put the plaintext password in a script file again, and now have the
> same problem.
>
> Remember, the old way of doing this was with rsh and .rhosts files,

Trusting the host is quite different, this can also be done with ssh (in a
much more secure fashion relying on the host-keys, not just the name).

> and those were a problem because DNS could more easily be compromised,
> and the system tricked into letting you in. SSH keys are meant to get
> around THAT problem.

No they are not.

> Otherwise, all the secret keyfiles are protected
> using restrictive permissions,

Wrong again, keys are typically protected by encryption. Unix file access bits
are just a dumb<tm> idea.

/Peter
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