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Old 04-15-2008, 05:56 AM
Clint Dilks
 
Default SSH Question relating to Public and Private Keys

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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Old 04-15-2008, 06:06 AM
Morten Nilsen
 
Default SSH Question relating to Public and Private Keys

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 ?


Certainly, adding passphrases nudges the security up a step, as
otherwise a compromised account means the offender can log onto any
other system - or in the case of compromised root, can log in anywhere
as anyone..


It comes down to, like all security measures, a balancing act between
security and ease-of-use.. You need to take into consideration what data
is around the systems, and what the worst case scenario would be..


--
Cheers,
Morten
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Old 04-15-2008, 08:23 AM
"Daniel de Kok"
 
Default SSH Question relating to Public and Private Keys

On Tue, Apr 15, 2008 at 7:56 AM, Clint Dilks <clintd@scms.waikato.ac.nz> 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 ?

Sure. In the first case someone would only need the key to get into a
machine, in the second case you need a key and a passphrase.

Of course, that's stating the obvious, but it clearly adds a layer of
security. So, do you want to trade security for comfort? I wouldn't,
but that's your choice to make.

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

While asymmetric cryptography is slow, the RSA keys are used to
exchange keys for (fast) symmetric cryptography. So, it's usually a
good idea to create large keys. Fortunately, the default in OpenSSH is
2048, which seems to be a fair key size.

-- Daniel
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Old 04-15-2008, 09:13 AM
"William L. Maltby"
 
Default SSH Question relating to Public and Private Keys

On Tue, 2008-04-15 at 17:56 +1200, 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 ?

Keeping in mind what the other responders have said, you need to do at
least an informal risk analysis to determine whether it is worth the
effort. Without going into all the formalities of assessment, reduction,
acceptance, assignment, ...

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.).

How effectively will the enhanced procedures be used? Will users
frequently try to bypass them because it is inconvenient etc.?

OT: does the political environment (e.g. management) support increased
security or does it view increased security as an inconvenient thing
they view as really unnecessary in their situation?

>From a purely technical POV, it is as the other responders have said.
Having *decent* pass phrases is certainly worthwhile.

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

Unless you are in an environment that is a desirable target for
espionage (corporate, military, ...) the default sizes are sufficient
IMO.

>
>
> Thanks for any thoughts, and have a nice day
> <snip sig stuff>

--
Bill

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