It sort of already is. This behavior is only applied to sessions with a TTY and then the client can disable it, which is a sensible default. This specific use case is tripping it up obviously since the server knows ahead of time that the connection is not important enough to obfuscate and this isn't a typical terminal session, but in almost any other scenario there is no way to make that determination and the client expects its ObscureKeystrokeTiming to be honored.

Yes, but I wouldn't be surprised if the change is rejected. The crypto library is very opinionated, you're also not allowed to configure the order of TLS cipher suites, for example.

+1... Given how much SSH is used for computer-to-computer communication it seems like there really should be a way to disable this when it isn't necessary.

Threats exist in both trusted and untrusted environments though.

This feels like a really niche use case for SSH. Exposing this more broadly could lead to set-it-and-forget-it scenarios and ultimately make someone less secure.

It made the front page when it was added.

https://news.ycombinator.com/item?id=37307708

Even if the chatbot served only as a Rubber Ducky [1], that's already valuable.

I've used Claude for debugging system behavior, and I kind of agree with the author. While Claude isn't always directly helpful (hallucinations remain, or at least outdated information), it helps me 1) spell out my understanding of the system (see [1]) and 2) help me keep momentum by supplying tasks.

[1] https://en.wikipedia.org/wiki/Rubber_duck_debugging

AIs are exceptional at sensing personalities from text. Claude nailed it here, the author felt so good about the "holy cow" comments that he even included them in the blog post. I'm not just poking this, but saying that the bots are fantastic sycophants.

I'm anti-LLM in most cases, but:

> I bet this mystery could gave been solved much quicker by simply looking at the packet capture in Wireshark.

For some people who are used to using Wireshark and who know what to look for, probably yes. For the vast majority of even technical people, probably not.

In my case, I did a packet capture of a single keystroke using tcpdump and imported it into Wireshark and I get just over 200 'Client: encrypted packet' and 'Server: encrypted packet' entries. Nothing useful there at all. If I tcpdump the entire SSH connection setup from scratch I get just as much useful information - nothing - but, oddly, fewer packets than my one keystroke triggered.

So yeah, I dislike LLMs entirely and dislike the reliance on LLMs that we see today, but in this case the author learned a lot of interesting stuff and shared it with us, whereas without LLMs he might have just shrugged and moved on.

Unfortunately with SSH specifically, the dissectors aren't very mature - you only get valid parsing up to the KeX completion messages (NEWKEYS), and after that, even if the encryption is set to `none` via custom patches, the rest of the message flow is not parsed.

Seems because dumping the session keys is not at all a common thing. It's just a matter of effort though - if someone put in the time to improve the SSH story for dissectors, most of the groundwork is there.

Asking an LLM about SSH (hint: the two S-es stand for security) would tell you why only having packet capture in Wireshark isn't going to reveal shit.

obviously OPs empirical and analytical rigor are top notch. He applied LLMs in the best way possible: fill gaps with clumsy command line flags or protocol implementations. Those aren't things one needs to keep in their head all the time.

Way to gatekeep. God forbid people use tools to help them investigate instead of knowing the exact approach to take.

How much are you staking on that bet?

Oh wow - I've never heard of TCP_CORK before. Without disabling pings I'd still pay the cost of receiving way more packets, but maybe that'd be tolerable if I didn't have to send so many pongs. This is super handy; excited to play around with it.

I am aware of TCP_NODELAY (funny enough I recently posted about TCP_NODELAY to HN[1] when I was thinking about it for the same game that I wrote about here). But I think the latency hit from disabling it just doesn't work for me.

[1] https://news.ycombinator.com/item?id=46359120

Can you explain how TCP_CORK helps here? The chaff packets are spaced 20ms apart and sent per socket, so I don’t see how TCP_CORK could help unless it coalesced across 20ms intervals? But coalescing is clearly not an option for the intended obfuscation effect of the original feature.

Haven't heard of TCP_CORK, very interesting.

For people who don't feel like googling it:

1. You TCP_CORK a socket

2. You put data into it and the kernel buffers it

3. If you uncork the socket, or if the buffer hits MSS, the kernel sends the packet

Basically, the kernel waits until it has a full packet worth of data, or until you say you don't have any more data to send, and then it sends. Sort of an extreme TCP_YESDELAY.

See https://catonmat.net/tcp-cork for where I learned it all from.

I seem to hit this logic often recently for some reason.

There are two issues with it:

- a primary is not a totality: if "security is the #1 consideration for SSH", that implies there's a #2, maybe even a #3 and so on consideration. So the question that follows becomes tautological: "but if the author doesn't need security, why use ssh?" -> surely for one or more of the #2, #3, etc. considerations, right?

- overabstraction (*): you ended up strawmanning the author. What they had issue with was keystroke timing obfuscation, which is a privacy feature. Timing attacks are (in part) a privacy concern, and privacy is a security concern, yes, but security is not just privacy concern, and privacy concerns are not just about timing attacks; these groups are not equal. For example, they might very well want the transmitted keypresses themselves to remain confidential, or they might very well want to retain cryptographic assurance of their integrity. These are security features they can continue to utilize by sticking with SSH.

All of this is to say, it's not even necessarily them using SSH for a hypothetical #2 or #3 (...etc...) reason, but likely because they still very much want to make use of large chunks of #1, which disabling keypress obfuscation does not actually rid SSH of, only at most weakens it in ways they clearly seem to be okay with.

(*) although if I zoom out enough, this is once again just "a primary is not a totality", just implicitly

> For example, "nc" (netcat) is pre-installed on all platforms where ssh is.

This is technically incorrect, because Windows now includes SSH too!

Typing with an extra 50ms latency will be fairly unpleasant.

> send all typed characters at 50ms intervals

Wouldn't this just change the packet interval from 20ms to 50ms? Or did you mean a constant stream of packets at 50ms intervals, nonstop?

I think the idea behind the current implementation is that the keystrokes are batched in 20ms intervals, with the optimization that a sufficiently long silence stops the chaff stream, so the keystroke timing is obfucated with an increased error bar of 20ms multiplied by number of chaff packets.

Yes! While this post was written entirely by me, I wouldn't be surprised if I had "smoking gun" ready to go because I spent so much time debugging with Claude last night.

ChatGPT too. And "lines up perfectly" when it doesnt actually line up with anything

Or the "Eureka! That's not just a smoking gun, it's a classic case of LLMspeak."

Grok, ChatGPT, and Claude all have these tics, and even the pro versions will use their signature phrases multiple times in an answer. I have to wonder if it's deliberate, to make detecting AI easier?

I'm working on a little SRE agent to pre-load tickets with information to help our on-call and I'm already tired of Claude finding 'smoking guns'.

I've love to delve into that.

https://pshapira.net/2024/03/31/delving-into-delve/

Without knowing how LLM's personality tuning works, I'd just hazard a guess that the excitability (tendency to use excided phrases) is turned up. "smoking gun" must be highly rated as a term of excitability. This should apply to other phrases like "outstanding!" or "good find!" "You're right!" etc.

They love clichés, and hate repeating the same words for something (repetition penalty) so they'll say something like "cause" then it's a "smoking gun" then it's something else

You might see certain phrases and mdashes ;-) rather often, because … these programs are trained on data written by people (or Microsoft's spelling correction) which overused them in the last n years? So what should these poor LLMs generate instead?

I don't think claude has even once used this in my conversations (Claude Desktop, Claude Code, Voice conversations...) Sycophancy, yes absolutely!

Maybe it has something to do with your profile/memories?

smoking gun, you're absolutely right, good question, em dash, "it isn't just foo, it's also bar", real honest truth, brutal truth, underscores the issue, delves into, more em dashes, <20 different hr/corporate/cringe phrases>.

It's nauseating.

Yes, it’s kind of a corpus delicti. ;)

At this I'm just so glad that "you're absolutely right!" phase is over.

I see it from GPT5 too a lot

It's a smoking gun of Claude usage.

> Speaking of smoking guns

Oh shoot! A shooting.

So the TL;DR of this post is: don't change this setting unless you know what you're doing.

Chastise it with a reminder that you're using smokeless powder.

the obtuseness is the point! This is true of a lot of my work[1][2][3].

The problems you run into when doing things you shouldn't do are often really fun.

[1] https://news.ycombinator.com/item?id=42342382

[2] https://news.ycombinator.com/item?id=37810144

[3] https://news.ycombinator.com/item?id=42674116

Yea UDP is technically more performant, but then you need a crypto layer + reliable message delivery layer + bespoke client. Using a plain old SSH client is cool.

However, there are existing libraries for exactly this use case - see https://github.com/ValveSoftware/GameNetworkingSockets

I guess QUIC libraries would also work.

https://news.ycombinator.com/item?id=37307708

2023 discussion about it here.

> It is trivial to do 10x that packet per second rate.

When making this statement, are you taking into account that SSH encrypts the traffic by default?

You surely mean the latency in its embedded terminal and not the code editor, right? I use VSCode’s remote SSH specifically so that code editing doesn’t suck. It really does not.

That doesn't sound right to me. This obfuscation isn't about a side-channel on a crypto implementation, this is about literally when your keystrokes happen. In the right circumstances, keystroke timing can reduce the search space for bruteforcing a password [1] but it's overstating to describe that as broken encryption.

[1] https://people.eecs.berkeley.edu/~daw/papers/ssh-use01.pdf

They literally explain the mechanism in the post and then explain why the security tradeoff made sense for their ssh game………

It is to prevent timing attacks but there are many ssh use cases where it is 100% computer to computer communications where there is no key based timing attack possible.

The fix seems kind of crazy though, adding so much traffic overhead to every ssh session. I assume there's a reason they didn't go that route, but on a first pass seems weird they didn't just buffer password strokes to be sent in one packet, or just add some artificial timing jitter to each keystroke.

But they'd have to be on the same network as me to do that attack, right?

Is it possible that this is on your end?

The extension is "ping@openssh.com." It shows up in the blog reliably for me across several browsers and devices.

It's vibe coded

I agree with your general point that most companies/projects do a terrible job optimizing for slow computers/networks, but OpenSSH is from the OpenBSD people, who are well-known for supporting ancient hardware [0]. Picking a random architecture, they fully support a system with only 64MB of memory [1], and the base install includes SSH. So I suspect that OpenSSH is fairly well tested on crappy computers/networks.

[0]: https://www.openbsd.org/plat.html

[1]: https://www.openbsd.org/landisk.html#hardware

There's a good chance you have other options. Regardless of how you feel about the company's head, Starlink would probably be one of them, with likely better performance than you're dealing with on ADSL.

But you cannot just sue a company because their network connected software doesn't work well on slow networks. Let alone a project like OpenSSH. It would be like me suing a game studio because my PC doesn't meet their listed minimum requirements to play the game.

You're not ok with a security/privacy tool using defensive techniques because of ... the lack of fiber in Africa?

The openssh team does not owe you anything.

If you want a “1990s” mode, add it yourself or pay some to do it for you.

> One thing you notice if you have ADSL

This is funny to me, because ADSL used to be the fast thing, as opposed to dialup modems.

You just opened a huge nostalgia portal, never thought that Dreamweaver would still be around, I used that somewhere around 2003 I believe. Good memories

Telnet nowadays typically isn’t available by default for security reasons, and OP wants people to be able to play the game just by typing “ssh thegamehost”.

Why not? If it's high-performance, it's fine.