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Yeah the lack of mentioning a CRL at all really stood out when reading this. I actually didn't know about SSH certificates until I saw this article (I always as
by digitallyfree 5y ago
Yeah the lack of mentioning a CRL at all really stood out when reading this. I actually didn't know about SSH certificates until I saw this article (I always assumed that SSH did not support this), but do run my own CA and authentication for internal web services, EAP-TLS, and VPN. The CRL is your first line of defense in the sense that it blocks the use of that credential instantly when it is revoked.
I will argue though that the use of a short expiry produces slightly better protection than no expiry at all. If an employee leaves the company (with no CRL in place) and their certs expire in 16 hours, then unless their credentials are stolen in that timeframe your systems are still safe.
Likewise, if a CRL is in place and credentials are stolen without you being aware of it, the expiry still provides a form of buffer if the stolen credentials end up being used after the cert expires. In this case the expiry would trigger before you realised that credentials were stolen and updated the CRL. Now yes compromises can happen in seconds, but that's not in every single case.
That being said I definitely agree that the expiry is not a subsitute to a CRL and any certificate system should have revocation systems in place. In the end you really should have both a CRL and expiry date if possible.
- imwillofficial 5y agoIf you didn’t know about SSH certs, you shouldn’t be giving advice. You should study the fundamentals
- OrvalWintermute 5y agoI think you may also have missed the context that he/she used, as they described running an x509 CA first. In an organizational context, many organizations are not going to jump to creating a novel CA type (SSH CA) when in fact regular x509 CAs are well known and the basis for much security, and many in regulated industries are using them already. Additionally, given that he/she is running an x509 CA, telling someone with that experience to study the fundamentals is not very polite. It assumes the author of the comment is not educated, but the very description of his/her use-cases are not simplistic ones. Engineering is all about tradeoffs after all.
- blueflow 5y agoYour pronoun thing makes your text painful to read.
- jjulius 5y ago... it genuinely pains you to read "he/she"?
- deleted 5y ago[deleted]
- egberts1 5y agoThat’s why I use “one”.
- OrvalWintermute 5y agoI just didn't want to assume gender, and didn't want to go through comment history in order to find it.
- rfrey 5y agoYou would seem to have a very low pain threshold.
- imwillofficial 5y agoThat’s a fantastic point. Mea culpa
- digitallyfree 5y agoI'm not familar with SSH certificates, but I do know the fundamentals of certificate-based authentication. If you don't have a way to revoke the cert, then the server will assume that your properly signed unexpired certificate is valid. You will need some way to let the server know that the previously issued cert is not valid anymore. This is how this type of authentication works, and the article did not address the important case of wanting to revoke a user's credentials.
- blueflow 5y agoRookie mistake: SSH has no CRL, it has an KRL. And its actually a separate thing since it operates largely independently from the CA. I have one in place. Used it once to terminate access for someone.
- OrvalWintermute 5y agoIt sounds like you could be making the rookie mistake instead by not reading what he/she actually wrote. > Yeah the lack of mentioning a CRL at all really stood out when reading this. I actually didn't know about SSH certificates until I saw this article (I always assumed that SSH did not support this), but do run my own CA and authentication for internal web services, EAP-TLS, and VPN. The CRL is your first line of defense in the sense that it blocks the use of that credential instantly when it is revoked. This sounds like he/she is running an x509 CA. He/she is generating certs for various use-cases. It is possible to use x509 certs with SSH of course, and so he/she could leverage his/her pre-existing CA for that function. Given above context CRL is completely accurate. And, KRL is not.
- egberts1 5y agoNo, SSL CA certificate are in no way like OpenSSL CA issued ones. The format of the certificate have diverged between two ecospheres about a decade ago.
- pritambaral 5y agoRookie mistake: SSH's KRL is also a CRL. See KEY REVOCATION LISTS in ssh-keygen(1). You can revoke plain keys with it, but also revoke certs (both by serial number and identity) with it. The infrastructure I built for access control using SSH certs used it. I know it works because I tested for it specifically.