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SSH hardening guide bonus edition: Disable password login if you can, leave the algorithm settings as they are and use an up to date version of OpenSSH. OpenSS

by hannob 5y ago

SSH hardening guide bonus edition: Disable password login if you can, leave the algorithm settings as they are and use an up to date version of OpenSSH. OpenSSH already agressively deprecates algorithms that are problematic. None of the algorithms enabled by default has any known security issue. But your manual tweaks from a random document you read on the Internet may enable an algorithm that we may later learn to be problematic.

ipaddr 5y ago
Safest setup disable password login. disable ssh login. Put the computer back in the box and put the box under your bed.
- 0xdeadb00f 5y ago
  Then, using aluminum foil and unfolded crisp packets make your room into a Faraday cage. Never open the door for any reason whatsoever. In fact, remove the door altogether.
  - 0xFFFE 5y ago
    Ensure lead bricks are used to build the said room.
    - doubled112 5y ago
      Lead is good, but I think it'd be easy to melt through. Better add another layer of something more temperature resistant. Defense in depth.
  - lizknope 5y ago
    I absolutely disable sshd on machines where I never need to login remotely like my laptops. My servers of course run sshd.
acatton 5y ago
In the same vein, protecting your SSH server with spiped[1] does 99% of the job. (= No need to setup fail2ban, password auth is not a big deal anymore, protects against out-of-date SSH servers and/or zero-days exploits, ...) [1] https://www.tarsnap.com/spiped.html https://www.tarsnap.com/spiped.html
- tiffanyh 5y ago
  Is Spiped similar in-concept to a VPN?
  - cpach 5y ago
    Yes. When spiped was released (2011) there were no really good VPN solutions out there. Now there is WireGuard, but it wasn’t launched until 2016.
    - amarshall 5y ago
      OpenVPN may have its issues (complicated setup vs. e.g. Wireguard, but not vs. e.g. IPsec), but I wouldn’t call it “not good” and it predates spiped by a decade.
      - cpach 5y ago
        Ok. I don’t agree there. What I’ve heard from security experts is that WireGuard is vastly superior to OpenVPN. Addendum: OpenVPN was released in 2001 and there where lots of cryptography-related systems from that era that certainly didn’t age well – IMO OpenVPN is one of those examples.
        LukeShu 5y ago
        OpenVPN's encryption is just TLS. It uses OpenSSL for this, not rolling their own implementation. Yes, there are parts of SSL/TLS that haven't aged well, but... it's good enough for the world's web traffic.
        5y ago
BelenusMordred 5y ago
> None of the algorithms enabled by default has any known security issue. For the tinfoil among us, jump on the post-quantum key exchange train, there's little overhead, it still uses traditional elliptic curve crypto, best of both worlds. The jump-off: sntrup4591761x25519-sha512@tinyssh.org
- ilaksh 5y ago
  What's a post-quantum key exchange? I assume this is a real thing and not a reference to Devs or Lapsis or something?
  - tialaramex 5y ago
    So. All of today's practical public key crypto could be broken by a sufficiently powerful quantum computer - if one existed which today it does not - thanks to a trick called Shor's Algorithm. However, there are new public key algorithms that aren't affected by Shor's algorithm. Two problems. 1. They're all worse, they have huge keys for example, or they're slow, so that sucks. 2. We don't know if they actually work, beyond that Shor's algorithm doesn't break them on hypothetical Quantum Computers. Even if you decide you don't care about (1) and you're very scared of the hypothetical quantum computers (after all once upon a time the Atom Bomb was also hypothetical) you need to deal with (2). Post-quantum schemes like this for SSH generally arrange that by doing two things, they have the shiny new Quantum Resistant algorithms, but they also have an old-fashioned public key algorithm, and you need to break both to break their security. Either alone won't help you.
    - da_chicken 5y ago
      > All of today's practical public key crypto could be broken by a sufficiently powerful quantum computer - if one existed which today it does not That we know of. There are commercially available quantum computers [0] and there are roadmaps for commercial technology ramp up significantly [1]. Remember, that's a roadmap to projected commercial viability. It's hard to say what state actors are capable of right now. [0]: https://azure.microsoft.com/en-us/services/quantum/ https://azure.microsoft.com/en-us/services/quantum/ [1]: https://venturebeat.com/2020/12/09/ionq-roadmap-quantum-machine-learning-2023-broad-quantum-advantage-2025/ https://venturebeat.com/2020/12/09/ionq-roadmap-quantum-mach...
drclau 5y ago
Also, configure sshd to use blacklistd: https://docs.freebsd.org/en/books/handbook/firewalls/#firewalls-blacklistd https://docs.freebsd.org/en/books/handbook/firewalls/#firewa...

by hannob 5y ago

ipaddr 5y ago

Safest setup disable password login. disable ssh login. Put the computer back in the box and put the box under your bed.

0xdeadb00f 5y ago
Then, using aluminum foil and unfolded crisp packets make your room into a Faraday cage. Never open the door for any reason whatsoever. In fact, remove the door altogether.
- 0xFFFE 5y ago
  Ensure lead bricks are used to build the said room.
  - doubled112 5y ago
    Lead is good, but I think it'd be easy to melt through. Better add another layer of something more temperature resistant. Defense in depth.
- lizknope 5y ago
  I absolutely disable sshd on machines where I never need to login remotely like my laptops. My servers of course run sshd.

acatton 5y ago

In the same vein, protecting your SSH server with spiped[1] does 99% of the job. (= No need to setup fail2ban, password auth is not a big deal anymore, protects against out-of-date SSH servers and/or zero-days exploits, ...) [1] https://www.tarsnap.com/spiped.html https://www.tarsnap.com/spiped.html

tiffanyh 5y ago
Is Spiped similar in-concept to a VPN?
- cpach 5y ago
  Yes. When spiped was released (2011) there were no really good VPN solutions out there. Now there is WireGuard, but it wasn’t launched until 2016.
  - amarshall 5y ago
    OpenVPN may have its issues (complicated setup vs. e.g. Wireguard, but not vs. e.g. IPsec), but I wouldn’t call it “not good” and it predates spiped by a decade.
    - cpach 5y ago
      Ok. I don’t agree there. What I’ve heard from security experts is that WireGuard is vastly superior to OpenVPN. Addendum: OpenVPN was released in 2001 and there where lots of cryptography-related systems from that era that certainly didn’t age well – IMO OpenVPN is one of those examples.
      - LukeShu 5y ago
        OpenVPN's encryption is just TLS. It uses OpenSSL for this, not rolling their own implementation. Yes, there are parts of SSL/TLS that haven't aged well, but... it's good enough for the world's web traffic.
      - 5y ago

BelenusMordred 5y ago

> None of the algorithms enabled by default has any known security issue. For the tinfoil among us, jump on the post-quantum key exchange train, there's little overhead, it still uses traditional elliptic curve crypto, best of both worlds. The jump-off: sntrup4591761x25519-sha512@tinyssh.org

ilaksh 5y ago
What's a post-quantum key exchange? I assume this is a real thing and not a reference to Devs or Lapsis or something?
- tialaramex 5y ago
  So. All of today's practical public key crypto could be broken by a sufficiently powerful quantum computer - if one existed which today it does not - thanks to a trick called Shor's Algorithm. However, there are new public key algorithms that aren't affected by Shor's algorithm. Two problems. 1. They're all worse, they have huge keys for example, or they're slow, so that sucks. 2. We don't know if they actually work, beyond that Shor's algorithm doesn't break them on hypothetical Quantum Computers. Even if you decide you don't care about (1) and you're very scared of the hypothetical quantum computers (after all once upon a time the Atom Bomb was also hypothetical) you need to deal with (2). Post-quantum schemes like this for SSH generally arrange that by doing two things, they have the shiny new Quantum Resistant algorithms, but they also have an old-fashioned public key algorithm, and you need to break both to break their security. Either alone won't help you.
  - da_chicken 5y ago
    > All of today's practical public key crypto could be broken by a sufficiently powerful quantum computer - if one existed which today it does not That we know of. There are commercially available quantum computers [0] and there are roadmaps for commercial technology ramp up significantly [1]. Remember, that's a roadmap to projected commercial viability. It's hard to say what state actors are capable of right now. [0]: https://azure.microsoft.com/en-us/services/quantum/ https://azure.microsoft.com/en-us/services/quantum/ [1]: https://venturebeat.com/2020/12/09/ionq-roadmap-quantum-machine-learning-2023-broad-quantum-advantage-2025/ https://venturebeat.com/2020/12/09/ionq-roadmap-quantum-mach...

drclau 5y ago

Also, configure sshd to use blacklistd: https://docs.freebsd.org/en/books/handbook/firewalls/#firewalls-blacklistd https://docs.freebsd.org/en/books/handbook/firewalls/#firewa...