openssh unix dev - Sep 2019 - revoking ssh-cert.pub with serial revokes also younger certs

Hi Daminan!


Hmmm... thought about a little...

when i use -vvv with ssh-keygen -Qf i see "debug1:..." So i think,
debug
is compiled in.

ssh-keygen --help gives me

ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number] file ...

so... option -z is not the serial of the certificate, it is the
version-number of the KRL-File...

My openssh-Verision from Debian is 1:7.4p1-10+deb9u7. Maybe, this
openssh-version does not support revoking a certificate by it's
serialnumber. This leads me to the next question... The serial-number of
a certificate is uniq over all certificates, or is it allowed, to
increment serial-numbers for each certificate separate? How is the design?


thank you

jakob

Am 16.09.19 um 04:18 schrieb Damien Miller:
> On Fri, 13 Sep 2019, Jakob Sch?rz wrote:
>
>> Hi there!
>>
>> What am I doing wrong?
>>
>> I created a ssh-certificate
>>
>> id_user_rsa-cert.pub with this dump:
>>
>> id_user_rsa-cert.pub:
>> root at host # ssh-keygen -Lf id_user_rsa-cert.pub
>> ??????? Type: ssh-rsa-cert-v01 at openssh.com user certificate
>> ??????? Public key: RSA-CERT SHA256:kPitwgxblaUH4viBoFoozSPq9Pblubbedk
>> ??????? Signing CA: ED25519
SHA256:8p2foobarQo3Tfcblubb5+I5cboeckvpnktiHdUs
>> ??????? Key ID: "test at myhost.mydomain.example"
>> ??????? Serial: 18
>> ??????? Valid: from 2019-07-29T02:08:00 to 2020-07-28T02:09:43
>> ??????? Principals:
>> ??????????????? test
>> ??????? Critical Options: (none)
>> ??????? Extensions:
>> ??????????????? permit-X11-forwarding
>> ??????????????? permit-agent-forwarding
>> ??????????????? permit-port-forwarding
>> ??????????????? permit-pty
>> ??????????????? permit-user-rc
>>
>>
>> Now i try to revoke this certificate with
>>
>> ssh-keygen -s ../user_ca.pub -kf /etc/ssh/revoked_keys -z 17
>> id_user_rsa-cert.pub
>>
>> The serial is 1 less the serial of my created certificate
>>
>> Check, if my certificate is valid
>>
>> root at host # ssh-keygen -Qf /etc/ssh/revoked_keys
id_user_rsa-cert.pub
>> id_user_rsa-cert.pub (test on myhost - created by ansible
(1564358942)):
>> REVOKED
>>
>> Why? I thougt, when i use -s <Serialnumber> only this specific
>> certificate for a pubkey is revoked...
> If you compile krl.c with -DDEBUG_KRL=1 then you can get some extra
> debugging that might show what is going on. You'll probably need to
> add -vvv to ssh-keygen's flags too.
>
> -d
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> openssh-unix-dev mailing list
> openssh-unix-dev at mindrot.org
> https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
-- 
lore ipsum

On Mon, 16 Sep 2019, Jakob Sch?rz wrote:
> Hi Daminan!
> 
> Hmmm... thought about a little...
> 
> when i use -vvv with ssh-keygen -Qf i see "debug1:..." So i
think, debug
> is compiled in.
debugging is compiled in generally, but the the recipe I mentioned turns
on extra KRL debugging.
> ssh-keygen --help gives me
> 
> ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number] file ...
> 
> so... option -z is not the serial of the certificate, it is the
> version-number of the KRL-File...
oops, yes.
> My openssh-Verision from Debian is 1:7.4p1-10+deb9u7. Maybe, this
> openssh-version does not support revoking a certificate by it's
> serialnumber.
It almost certainly does, but you'd need to use a KRL specification file.
See the "KEY REVOCATION LISTS" section in the ssh-keygen manpage.
> This leads me to the next question... The serial-number of
> a certificate is uniq over all certificates, or is it allowed, to
> increment serial-numbers for each certificate separate? How is the design?
what goes in the serial number is totally up to the CA. OpenSSH doesn't
make any authentication decisions based on it - it's in the certificate
mostly to allow very compact revocation lists.

-d

Thank you for your answer.

Am 17.09.19 um 02:02 schrieb Damien Miller:
> On Mon, 16 Sep 2019, Jakob Sch?rz wrote:
>
>> Hi Daminan!
>>
>> Hmmm... thought about a little...
>>
>> when i use -vvv with ssh-keygen -Qf i see "debug1:..." So i
think, debug
>> is compiled in.
> debugging is compiled in generally, but the the recipe I mentioned turns
> on extra KRL debugging.
I think, it's not necessary now.
>
>> ssh-keygen --help gives me
>>
>> ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number] file
...
>>
>> so... option -z is not the serial of the certificate, it is the
>> version-number of the KRL-File...
> oops, yes.
This means, with -z i can give my KRL-File a serial-number? How can i
dump the revoke-file infos?
>
>> My openssh-Verision from Debian is 1:7.4p1-10+deb9u7. Maybe, this
>> openssh-version does not support revoking a certificate by it's
>> serialnumber.
> It almost certainly does, but you'd need to use a KRL specification
file.
> See the "KEY REVOCATION LISTS" section in the ssh-keygen manpage.
This section is not clear enough. Please add some
examples.
>
>> This leads me to the next question... The serial-number of
>> a certificate is uniq over all certificates, or is it allowed, to
>> increment serial-numbers for each certificate separate? How is the
design?
> what goes in the serial number is totally up to the CA. OpenSSH doesn't
> make any authentication decisions based on it - it's in the certificate
> mostly to allow very compact revocation lists.

I played around a little. I have a bunch of different certificates
(different users, rsa, ecdsa, ed25519-keys...). Some with the same
serial-number, some with different. I set up my CA to increment each
certificate for each pubkey separate. This means, The pubkey
id_userA_rsa.pub and id_userA_ecdsa.pub start with 1 and each counts up
for itself.

Then i tried to revoke the certificate for id_userA_rsa.pub
(id_userA_rsa-cert.pub) with serial 8. The KRL says, i have to fill one
line with

??? serial: 8

i can not add a key-id to the serial-number. Only "serial: 8" is
possible.
When i check, if certificate is revoked with

??? ssh-keygen -Qf ... i get a "REVOKED". It's ok.

id_userA_ecdsa-cert.pub has serial 9, so this certificate is not
revoked. But if it has also serial 8, both certificates are revoked.

If i write

??? id: userA at hostX

in my KRL, all certificates for this pubkey (id) are revoked,
independend from their serial. Its the same effect as if i give the path
to id_userA_rsa-cert.pub or id_userA_rsa.pub.
So if i wand a clean an proper revokation of old certificates, there
MUST be only one incremental-line over all certificates.

This is NOT clear in the man-pages.

Would i be possible, that someone update the docs, that it gets a bit
more understandable for newbies (as me).

thank you


Jakob