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points by Ecco 2 days ago | 0 comments

How is password auth weaker than key auth? Bugs in auth code can happen in both pathways. And apart from stupidly short passwords both should be equally impossible to brute-force.

In other words, conceptually, at the end if the day, isn’t a key just another name for a password, really?

[–] minitech 2 days ago

Password gets sent to the server. Private key does not get sent to the server, and authentication protocol can be forwarded safely, enabling things like ssh-agent, FIDO SSH keys. This is solvable with passwords (see: augmented PAKE), but `PasswordAuthentication` isn’t that. But there are also settings where none of this really matters, yes, to be fair if that’s what you’re referring to.

SSH certificates are cool too.

[–] TZubiri 2 days ago

password doesn’t get sent to the server, hash does.

but I guess that the hash is always the same unlike with pub priv key mechanism.

[–] mkj 2 days ago

No. The password gets sent to the server. That said, I still enable passwords on servers, but don't ever share passwords between trust domains.

[–] traceroute66 2 days ago

> password doesn’t get sent to the server, hash does.

Kind of irrelevant what gets sent to the server and what happens on the server.

Password is already easily defeatable long before it even leaves your computer, thanks to keyloggers and/or password manager breaches and/or old-school shoulder surfing (assisted in the 2026 era by covert filming and AI).

All of which are not vulnerabilities with hardware-backed keys which you don't even need a Yubikey for these days since most modern computers and smartphones have secure enclaves and/or TPMs. (Yubikeys are still great though).

[–] Borealid 2 days ago

What people think of as a very strong password often has <100 "security bits" of entropy.

Keys are usually at least 128 bits of entropy, and it's easy to take them up to 256.

Yes, both are a shared secret, but password auth - even with challenge-response - is weaker than key auth exactly because key auth provides more guess resistance.

[–] Elucalidavah 2 days ago

But the SSH keys are based on asymmetric crypto, not shared secrets.

[–] dagss 2 days ago

That makes it impossible to steal the key if you MITM, but there is still the same chance of guessing it. (Assuming password has as many bits of pure randomness, such as machine generated password.)

[–] traceroute66 2 days ago

> What people think of as a very strong password often has <100 "security bits" of entropy.

The best password in the world will still be defeated by a simple keylogger or breach of your password manager.

[–] Borealid 21 hours ago

The best cryptographic key in the world would be defeated by a breach of your filesystem.

The comparison here is between in-memory cryptographic keys and in-memory passwords. Yeah typing a password into a keyboard adds a vulnerability in between the keyboard and the computer, but it's not a huge difference in security posture. If the device using the secret is compromised, so is the secret, whether it came from the user's mind or not, whether it was stored encrypted before the user used it or not.

A physically separate hardware security module does add protection but I think that's a different conversation.

[–] scotty79 2 days ago

2^100 is a lot of things to try though

[–] jandrese 2 days ago

Especially if you have Fail2Ban set up.

[–] traceroute66 2 days ago

> if you have Fail2Ban set up.

Worth noting that if you are running a remotely recent version of SSH it has everything you need built-in. No need for Fail2Ban on SSH these days if your config is fully modernised.

[–] Borealid 1 day ago

Could you maybe explain a bit more about how one sets up OpenSSH to block brute-force login attempts with only its built-in features?

[–] traceroute66 1 day ago

> Could you maybe explain a bit more about how one sets up OpenSSH to block brute-force login attempts with only its built-in features?

There are various ways, but you will probably want to start by investigating a combination of the below tuned for your environment :

      - PerSourceMaxStartups
      - PerSourceNetBlockSize
      - PerSourcePenalties
      - Match Invalid-User + RefuseConnection

`PerSourcePenaltyExemptList` is also worth a mention if its the sort of thing you like, we don't use it at $work as whitelisting IP ranges is not really in-line with modern security best-practice (zero trust etc.).

[–] belorn 2 days ago

Fail2Ban is kind of required unless one like running out of sockets and are unburden by high cpu and disk load.

[–] jandrese 2 days ago

There is regular bot traffic attacking SSH, but it's not "saturate your downlink" level of traffic. If you're getting attacked that heavily then you're being specifically targeted.

[–] Aachen 2 days ago

Huh? I run ssh (OpenSSH) on port 22 with root login enabled and no fail2ban on a single-core laptop cpu from fifteen years ago. The load average is 0.00 even with the small mail and web server that runs on it

What cpu and especially what disk load are you talking about? Also not running out of sockets, not sure if that's RAM-dependent (the box has 2GB)

[–] belorn 2 days ago

Working as a sysadmin, and with disk encryption the constant log writes generated from ssh was enough to cause heavy load on severs. Long lasting connections from bots also forced us to increase the maximum number of sockets, as some scan waves was enough to hit the maximum and block other connections. Fail2ban has mitigated those issues to the point where neither has been an issue.

[–] teddyh 2 days ago

I believe this depends on your exposure level. If you have one, or maybe no, domain names pointed at your server, you are probably fine. If you have tens, or hundreds, of domains pointed at your server (i.e. you are a web site hoster), you will probably need something like fail2ban.

[–] Aachen 1 day ago

On another server with the same setup, there's various services and websites running, so load average is never zero there (due to scrapers) but ssh has yet to catch my eye in htop. Whenever I've looked, even the amount of cpu that a Windows VM uses constantly while idle is many times higher than what ssh uses

[–] 8organicbits 2 days ago

Password reuse is the problem. The password hash is stolen from some other site and brute forced offline.

[–] dwedge 2 days ago

Same issue with key reuse. Unless you have a policy to rotate them and verify which host they login from, someone's unencrypted hard drive from 5 years ago is more likely to have a key than password.

[–] traceroute66 2 days ago

> someone's unencrypted hard drive from 5 years ago is more likely to have a key than password.

Even 5+ years ago, hardware-backed SSH keys were a thing (Yubikey). The only difference today is that its 100% easier to do keys properly because of the widespread commoditisation of secure enclaves in desktops and smartphones to support FIDO, its basically free of charge now because you're not obliged to buy a Yubikey.

[–] epihelix 2 days ago

> How is password auth weaker than key auth?

Well, it's a heck of a lot weaker in this instance (at least when `PasswordAuthentication no`)

[–] ahepp 1 day ago

In this specific instance yes, but it seems like it could have about as easily been a perfect cascade of failures in janky libc routines for checking keys as opposed to janky libc routines checking passwords.

[–] ant0ni 2 days ago

you claimed my favorite game's character name!