revoking ssh-cert.pub with serial revokes also younger certs

[Jakob Schürz]

Thank you for your answer.

Am 17.09.19 um 02:02 schrieb Damien Miller:
> On Mon, 16 Sep 2019, Jakob Schürz 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