openssh unix dev - Dec 2018 - RFE: OpenSSH Support for PKCS11 Funneling to PAM for Kerberos/PKINIT

I know OpenSSH currently supports PKCS11 devices (such as smartcards)
for publickey authentication, but I would love to see PKCS11 extended
further.  It is currently possible to perform PKCS11 certificate
authentication, via pam_krb5.so (on Linux at least and likely something
similar on other *NIX) which allows smartcard auth to a Kerberos
(including AD) server, where a TGT can also be granted.  How difficult
would it be to add functionality to OpenSSH so that it can funnel PKCS11
certs from SSH client to server and on to PAM where it could be used by
Kerberos/PKINIT?  My thought is that this is at least part way there
with the current PKCS11 support but I won't claim to be an expert
regarding the internals of what would be needed.  I would think that a
number of places using smartcards (I currently work for a gov agency
that uses smartcards) would find this approach to have additional
security and management features (given real-time validation against a
kerberos/AD server) over using publickey auth (based on PKCS11) and also
having the added benefit of granting a TGT on sign-in, enabling SSO
(GSSAPI) to additional backend servers.

What are thoughts on this functionality being added to OpenSSH?  Am I
the first to suggest such a thing?


Jim

Hi,

Maybe I am wrong, but I believe you did not get it right.

You should use PKCS#11 to perform PKINIT in order to authenticate
against the KDC to acquire TGT.
Then ssh can use the TGT in order to issue ticket to access remote
sshd using GSSAPI KEX.

If you like to use pam_krb5 locally on your system to issue the TGT,
do it... it yet another method to have TGT in your user context. The
ssh command will use the TGT (or available keytab) to interact with
sshd, without requiring any special pam module at the remote side.

You can delegate your TGT using forwarded TGT into the remote machine
if you need to jump additional hope.

In other words, kerberos is SSO technology, the PK is used at
authentication phase only and if smartcards are being used this phase
is performed on local machine, once TGT is available, the remaining of
the interaction is kerberos only.

Regards,
Alon

On Wed, Dec 19, 2018 at 1:10 AM mailto428496 <mailto628496 at cox.net>
wrote:
>
> I know OpenSSH currently supports PKCS11 devices (such as smartcards)
> for publickey authentication, but I would love to see PKCS11 extended
> further.  It is currently possible to perform PKCS11 certificate
> authentication, via pam_krb5.so (on Linux at least and likely something
> similar on other *NIX) which allows smartcard auth to a Kerberos
> (including AD) server, where a TGT can also be granted.  How difficult
> would it be to add functionality to OpenSSH so that it can funnel PKCS11
> certs from SSH client to server and on to PAM where it could be used by
> Kerberos/PKINIT?  My thought is that this is at least part way there
> with the current PKCS11 support but I won't claim to be an expert
> regarding the internals of what would be needed.  I would think that a
> number of places using smartcards (I currently work for a gov agency
> that uses smartcards) would find this approach to have additional
> security and management features (given real-time validation against a
> kerberos/AD server) over using publickey auth (based on PKCS11) and also
> having the added benefit of granting a TGT on sign-in, enabling SSO
> (GSSAPI) to additional backend servers.
>
> What are thoughts on this functionality being added to OpenSSH?  Am I
> the first to suggest such a thing?
>
>
> Jim
>
> _______________________________________________
> openssh-unix-dev mailing list
> openssh-unix-dev at mindrot.org
> https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev

Alon,

I should have provided more background.  You are assuming that I could
perform the PKINIT prior to connecting to the SSH server.  In this case
(and others) there is an interest in not exposing the kerberos servers
to the world and thus someone connecting remotely would not be able to
obtain a TGT or do a PKINIT.  The goal would be for SSH to handle all
the auth and only after connecting to the SSH gateway server, and doing
a PKINIT as part of the process, then the user would have access to
kerberos and could obtain a TGT.


Jim


On 12/18/2018 06:18 PM, Alon Bar-Lev wrote:
> Hi,
>
> Maybe I am wrong, but I believe you did not get it right.
>
> You should use PKCS#11 to perform PKINIT in order to authenticate
> against the KDC to acquire TGT.
> Then ssh can use the TGT in order to issue ticket to access remote
> sshd using GSSAPI KEX.
>
> If you like to use pam_krb5 locally on your system to issue the TGT,
> do it... it yet another method to have TGT in your user context. The
> ssh command will use the TGT (or available keytab) to interact with
> sshd, without requiring any special pam module at the remote side.
>
> You can delegate your TGT using forwarded TGT into the remote machine
> if you need to jump additional hope.
>
> In other words, kerberos is SSO technology, the PK is used at
> authentication phase only and if smartcards are being used this phase
> is performed on local machine, once TGT is available, the remaining of
> the interaction is kerberos only.
>
> Regards,
> Alon
>
> On Wed, Dec 19, 2018 at 1:10 AM mailto428496 <mailto628496 at
cox.net> wrote:
>> I know OpenSSH currently supports PKCS11 devices (such as smartcards)
>> for publickey authentication, but I would love to see PKCS11 extended
>> further.  It is currently possible to perform PKCS11 certificate
>> authentication, via pam_krb5.so (on Linux at least and likely something
>> similar on other *NIX) which allows smartcard auth to a Kerberos
>> (including AD) server, where a TGT can also be granted.  How difficult
>> would it be to add functionality to OpenSSH so that it can funnel
PKCS11
>> certs from SSH client to server and on to PAM where it could be used by
>> Kerberos/PKINIT?  My thought is that this is at least part way there
>> with the current PKCS11 support but I won't claim to be an expert
>> regarding the internals of what would be needed.  I would think that a
>> number of places using smartcards (I currently work for a gov agency
>> that uses smartcards) would find this approach to have additional
>> security and management features (given real-time validation against a
>> kerberos/AD server) over using publickey auth (based on PKCS11) and
also
>> having the added benefit of granting a TGT on sign-in, enabling SSO
>> (GSSAPI) to additional backend servers.
>>
>> What are thoughts on this functionality being added to OpenSSH?  Am I
>> the first to suggest such a thing?
>>
>>
>> Jim
>>
>> _______________________________________________
>> openssh-unix-dev mailing list
>> openssh-unix-dev at mindrot.org
>> https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev