Secure Shell
Re: Multi Hopping by sshserver proxy with different keys Sep 27 2010 07:51AM
Nicolas Ferragu (nicolas ferragu laposte fr) (1 replies)
Richard,

Yes of course I could use remote command field but as I said before I
don't want to do a command like "ssh bastion ssh target" since I'd like
to use Putty as if I where connecting directly my target - ie I'd like
to use the bastion in a proxy way. In another words, I don't want
anything but telling Putty to connect to my target in the main field
Hostname.

Moreover, I don't want to deal with password's accounts since key
exchanges are mandatory in the project.

I think I gonna modify putty's code to make a direct remote command
proxy protocol.

Thanks for sharing,
NF

-------- Message original --------
Sujet: Re: Multi Hopping by sshserver proxy with different keys
De : Wilson, Richard <richard.wilson3 (at) hp (dot) com [email concealed]>
Pour : Nicolas Ferragu <nicolas.ferragu (at) laposte (dot) fr [email concealed]>, Stephen Dowdy
<sdowdy (at) ucar (dot) edu [email concealed]>
Copie à : "secureshell (at) securityfocus (dot) com [email concealed]" <secureshell (at) securityfocus (dot) com [email concealed]>
Date : 24/09/2010 21:55

> Nicholas,
>
> You might try using the PuTTY "Remote Command" field in the SSH panel to start a script on the Bastion

host that would check and see if an agent was running, and start one if
not.

I would recommend expect as the scripting language for this -- it
emulates an interactive session and

SSH is designed to not accept passphrases and passwords as parms.

You could pass the passphrase as a parm from the Windows host if your
security allows it and

avoid storing the passphrase on the bastion host.
>
> HTH,
>
> Richard Wilson
> Rich dot Wilson at hp dot com
>
> -----Original Message-----
> From: listbounce (at) securityfocus (dot) com [email concealed] [mailto:listbounce (at) securityfocus (dot) com [email concealed]] On Behalf Of Nicolas Ferragu
> Sent: Friday, September 24, 2010 3:01 AM
> To: Stephen Dowdy
> Cc: secureshell (at) securityfocus (dot) com [email concealed]
> Subject: Re: Multi Hopping by sshserver proxy with different keys
>
> Stephen,
>
> The problem is that my target key is on the gateway bastion host !
> The client don't have it. Moreover, the bastion's keys are protected by passphrases and served by ssh-agent. So can't do any agentforwarding at all..
>
> Otherwise, I've never succeeded in having key exchange between bastion and target while netcating in a proxycommand. It's ending systematically with an interactive password prompt (not passphrase).
>
> Of course the "ssh -t bastion ssh -t target" works well but I don't want to do it like that because I use a putty client which won't behave ergonomically if used that way.
> The same idea applies to your - however excellent - hackery you made with exclamation ! (I'm on Putty... Sorry for that).
>
> Once again this is a schematic view of what I want :
>
> Windows Linux Linux
> | | |
> Putty OpenSSH_5.6p1 Openssh any version
> | | |
> Client ----------> Bastion ----------> Target
> \_________________/ \________________/
> Client's Key bastion's key
> (Pagent) (ssh-agent)
>
> Summarizing my needs taking a similarity view like agentforwarding :
> I'd like to have an ssh-agent hopping.
>
>
>
> -------- Message original --------
> Sujet: Re: Multi Hopping by sshserver proxy with different keys De : Stephen Dowdy <sdowdy (at) ucar (dot) edu [email concealed]> Pour : Nicolas Ferragu <nicolas.ferragu (at) laposte (dot) fr [email concealed]> Copie à : secureshell (at) securityfocus (dot) com [email concealed] Date : 23/09/2010 19:26
>
>> Nicolas,
>>
>> If i understand your request, fully...
>>
>> I'll give you some info for OpenSSH (which you could use via Cygwin on
>> your windows client), but i don't know if PuTTY has similar
>> capability. (clearly, you've discovered plink.exe can do similar
>> things) (while this info may not apply directly to your problem, i
>> figure it'll be of general interest)
>>
>> ----------------
>> Host bastion
>> IdentityFile ~/.ssh/bastionkey
>> User bastionuser
>>
>> Host target
>> IdentityFile ~/.ssh/targetkey
>> User targetuser
>> ProxyCommand ssh bastion nc target 22
>> ----------------
>>
>> If you have both keys on the client, a
>>
>> ssh target
>>
>> will "do the right thing(tm)" here by finding the target directive,
>> indirectly resolving to a bastion connection using the bastion key,
>> then piggy-backing on the established bastion connection's netcat link
>> to the target and applying the target key.
>>
>> OpenSSH 5.5 or so has a builtin 'netcat' like facility using '-W
>> target:port', i haven't started using that yet, as my normal systems
>> (Debian Lenny) don't have that version.
>>
>>
>> Here's some hackery i have in my ~/.ssh/config file:
>>
>> -----------------------
>> # Multi-(user+host) arbitrary gateway hopping
>> # usera%hosta!userb%hostb[!userc%hostc...]
>> # STILL requires using '-l userd' for destination user on command line
>> (i.e. we ignore last # user in specification # e.g. ssh -l root
>> sdowdy@zia!root@umds0-vgw
>> Host *!*
>> GatewayPorts no
>> ProxyCommand
>> $(h="%h";p="%p";ruh=${h##*\!};rh=${ruh##*\%%};ru=${ruh%%\%%*};ru=${ru:
>> -${USER}};luh=${h%%\!*};lh=${luh##*\%%};lu=${luh%%\%%*};lu=${lu:-${USE
>> R}};echo ssh -l ${lu} ${lh} "\`type -p netcat nc | head -1\` ${rh}
>> 22") # h=host, p=port (expanded by openssh cmdline # ruh,rh,ru=remote
>> user+host, remote host, remote user (successively pulled off
>> right-hand-side) # luh,lh,lu=local user+host, local host, local user
>> (pulled off left-hand-side) #
>> -----------------------
>> This directive allows you, if you use a Bourne-Shell/posix-shell to
>> hop via an arbitrary number of [user@]host[!...] connections via
>> iterative deconstruction of the target specified within openssh.
>> If you have any required keys in your client ssh-agent, they'll be
>> appropriately applied down the chain. (be careful of shell
>> meta-character expansion of '!' -- I chose that after initially having
>> chosen '::' as the gateway delimiterd (DECnet style poor-mans
>> routing), and finding that while it worked for 'ssh', it DOESN'T work
>> for scp. '!' works for both ssh and scp.
>> You can use some other separator like "_", which isn't valid DNS.
>>
>> the \`type -p netcat nc | head -1\` is simply used to work on SLES and
>> *ever other* linux distro, since SLES uses 'netcat' (nc on SLES is
>> something else). That whole thing can be replaced with simply 'nc' if
>> you don't need to deal with SLES. (and that's the primary requirement
>> for a Bourne-alike shell.
>>
>>
>> If i'm using the "bastion" (gateway) host frequently for multiple
>> connections (i have a number of systems that have a backend RFC1918
>> network of compute nodes or data servers), i may use ControlMasters
>> like:
>>
>> Host gw1-* gw2-*
>> User blah
>> NumberOfPasswordPrompts 1
>> ConnectTimeout 60
>> ControlMaster auto
>> ControlPath ~/.ssh/%r@%h:%p.sock
>>
>> That way, i only authenticate once on the gateway host and use that
>> ControlMaster connection as the piggyback for subsequent connections
>> to that gateway and any hosts residing behind it. This is mainly
>> useful on systems where i'm required to enter a password, instead of
>> using authorized-key trust.
>>
>> --stephen
>>
>
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>
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>
>

Post-scriptum La Poste

Ce message est confidentiel. Sous reserve de tout accord conclu par
ecrit entre vous et La Poste, son contenu ne represente en aucun cas un
engagement de la part de La Poste. Toute publication, utilisation ou
diffusion, meme partielle, doit etre autorisee prealablement. Si vous
n'etes pas destinataire de ce message, merci d'en avertir immediatement
l'expediteur.

[ reply ]
Re: Multi Hopping by sshserver proxy with different keys Sep 27 2010 03:54PM
Jakub (evaver gmail com)


 

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