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Poll HN: Do you use SSH certificates (not mere public-key authentication)?

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Re: Poll HN: Do you use SSH certificates (not mere public-key authentication)?

#111

Post by chociej »

bongobingo1 wrote: post #89
iambvk wrote: post #68

Earlier quoted context omitted.

What is the benefit?

I think, 1) You don't have to ssh-copy-id to new boxes, which is nice. 2) You can de-auth a key for all machines by changing the DNS record. This would depend on some propagation time but perhaps you can point the resolver at your nameserver directly which would avoid that.

You could simply choose a short TTL, or your tool could check for e.g. "some-name._sshkeys.whatever.tld" as well as "_revoked.some-name._sshkeys.whatever.tld" to handle revocation instantly

Re: Poll HN: Do you use SSH certificates (not mere public-key authentication)?

#112

Post by gunapologist99 »

tptacek wrote: post #56
jerf wrote: post #16

We looked into them once at work for our "conventional" SSH infrastructure, but immediately rammed into the wall that a certificate can sign a key, but you can't have a full PKI infrastructure like SSL where certs can sign certs that can sign keys. Without the ability to delegate, the logistics of needing to create an absolutely centralized authority to do the useful things we wanted to do within the organization rai…

Essentially the whole point of modern SSH CAs is to centralize authentication and authorization for servers, and to keep long-lived keys off your developer machine fleet. If "no long-lived keys on laptops" and "central authority for who gets access to what with which credentials" aren't principles for your security practice, then you're right: there's not much of a win to switching to a CA model.

Sarcastic remarks like "if [mostly good things] aren't principles for your security practice" an strawman arguments seem a bit provocative for this type of debate.

Re: Poll HN: Do you use SSH certificates (not mere public-key authentication)?

#113

Post by egberts1 »

dotwaffle wrote: post #20

I store my authorized_keys in DNS TXT records, that are DNSSEC signed, with a validating resolver on the box. I then just use "/usr/bin/hesinfo %u ssh" as my AuthorizedKeysCommand in OpenSSH. I wrote a little tool that allowed you to "#include" other DNS records etc, but "hesinfo" is generally easily installable/available so it's just easier.

Yes. Hesiod is safer than DNS TXT once secured by DNSSEC, because I envision mass blocking of DNS TXT in the near future.

Re: Poll HN: Do you use SSH certificates (not mere public-key authentication)?

#114

Post by gunapologist99 »

tptacek wrote: post #98
Fnoord wrote: post #91

Earlier quoted context omitted.

DNSSEC is top-down securing chain, DNSCrypt bottom-up. Each has their pros and cons. Relying on your government to keep you secure can be a valuable factor, depending on your threat model.

Ok, these are words, but again I'm not talking about DNS security here, I'm talking about SSH key distribution. Why would you elect to have your key distribution controlled by the DNS PKI? What's the upside? The downside is, an actor with control over the DNS PKI (there are many of those; see, for instance, every DOJ seizure of a domain) gets a degree of control over your SSH authorized keys. Seems... bad?

Agreed completely. The threat model for DNSSEC is vast; why would you diminish the security of a perfectly good end-to-end model in SSH keys or certificates, as long as you control 100% of that infrastructure.

Introducing any outside actors at all objectively diminishes the security of the whole model by becoming another link in the chain, even if that link isn't necessarily the weakest (and I certainly believe it would be, because both DNSSEC and the public Certificate Authority industry are object lessons for the abject failure of highly centralized global, government-wide, or even just company-wide security), but simply increasing any of the surface area is enough to decrease the security of the system.

Re: Poll HN: Do you use SSH certificates (not mere public-key authentication)?

#116

Post by tptacek »

gunapologist99 wrote: post #112
tptacek wrote: post #56

Earlier quoted context omitted.

Essentially the whole point of modern SSH CAs is to centralize authentication and authorization for servers, and to keep long-lived keys off your developer machine fleet. If "no long-lived keys on laptops" and "central authority for who gets access to what with which credentials" aren't principles for your security practice, then you're right: there's not much of a win to switching to a CA model.

Sarcastic remarks like "if [mostly good things] aren't principles for your security practice" an strawman arguments seem a bit provocative for this type of debate.

There was absolutely nothing sarcastic about that remark. I wouldn't snark at 'jerf. Most security practices don't have those principles for SSH.

Thanks for calling it out though; if you read it that way, they might have too, which would be a little mortifying.

Re: Poll HN: Do you use SSH certificates (not mere public-key authentication)?

#117

Post by tehno »

Has anyone here implemented Google's HIBA (https://github.com/google/hiba) in addition to SSH CA/certs for the extra identity and grant checks?

I'm thinking about implementing HIBA with Vault managed SSH certs, and would appreciate anyone's comments about this approach.

Re: Poll HN: Do you use SSH certificates (not mere public-key authentication)?

#118

Post by blablabla123 »

xyzzyz wrote: post #103
blablabla123 wrote: post #97

Earlier quoted context omitted.

By doing a Certificate Signing Request (CSR) from the client. Not sure when it's actually worth doing this extra effort but with the right automation (e.g. with Ansible) it's doable. Never tried this for ssh though. Additional security if you use HSMs.

That actually doesn’t answer my question (though the actual addressee answered it already quite satisfactorily). First, there is no such thing as CSR in context of ssh certificates: ssh certificates are not x.509 certificates (known for their use in TLS). Second, even assuming that they were, a client creates a CSR with their key, and then what? Where is the root of trust? Who processes these CSRs? How is it deciding…

I mean ssh certificates can be x509, Azure VMs used to be provisioned with PEM actually, also PGP can be used. Not sure, I guess a use case could be to create client certificates remotely that are part of a certificate hierarchy. Obviously this doesn't solve any root of trust issues if the creation is initiated by the client.

Re: Poll HN: Do you use SSH certificates (not mere public-key authentication)?

#119

Post by cubesnooper »

xyzzyz wrote: post #104
cubesnooper wrote: post #41

Earlier quoted context omitted.

I have a Raspberry Pi dedicated to generating certificates. It serves the files to my LAN statically via a webserver, and is otherwise heavily firewalled. I don't run any other software on the Pi, so barring an exploit in the webserver, I’m not worried about the signing key getting compromised. Compared to my desktop, where over the years I ran all kinds of stuff from the package manager, downloaded Python scripts an…

So anyone on your LAN can visit the URL and download the CA private key? Isn’t it only marginally more secure than just keeping the private key on your workstation in the first place, and foregoing the entire rigamarole with certificates? I mean, if you are worried about your something compromising your workstation and stealing your individual private keys, nothing is stopping whoever compromised your workstation fro…

> So anyone on your LAN can visit the URL and download the CA private key?

No, the only files served to the LAN are the certificates, which contain the signatures by the CA of the public keys of other machines. Those are safe to distribute openly because they’re useless without the private key of the public key that was signed.

Re: Poll HN: Do you use SSH certificates (not mere public-key authentication)?

#120

Post by cubesnooper »

gunapologist99 wrote: post #88
cubesnooper wrote: post #42

Earlier quoted context omitted.

Rotation is actually a lot easier with certificates. I just generate a new key on the client, copy the public key to the CA, and I’m done, with no need to repopulate authorized_keys on all my other machines. In another comment I went into more detail about how I keep the CA secure.

> Rotation is actually a lot easier with certificates. I just generate a new key on the client, copy the public key to the CA, and I’m done, with no need to repopulate authorized_keys on all my other machines. Or, just paste your public key into your Userify profile and the same thing happens in seconds for every server that you have authorization for. Even better, there's no dependency on having a CA up and running…

I’m glad Userify works well for you. For my purposes, whipping up a couple of cronjobs involving curl and OpenSSH is more appropriate than relying on an external cloud service.

> But I've been burned before when a central auth server was down and I couldn't log into my servers

There is no central auth server involved here. My servers check login credentials against the CA’s public key, which is installed alongside my sshd config file. I make my certificates valid for three weeks, but regenerate them every two, so if some failure happens with creating or fetching certificates I have a week to notice and fix the problem.

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