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Why does SSH send 100 packets per keystroke?

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Re: Why does SSH send 100 packets per keystroke?

#61

Post by diath »

Veserv wrote: post #21

The really mysterious part is how ~10,000 packets per second costs ~20% of a core. That would mean SSH is bottlenecking in its code at ~50,000 packets per second per core which would be ~500 Mbps per core (assuming full packets) which is ludicrously slow. It is trivial to do 10x that packet per second rate. Is SSH really that poorly designed?

> 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?

Re: Why does SSH send 100 packets per keystroke?

#62

Post by [deleted] »

convolvatron wrote: post #36
ycombinatrix wrote: post #33

Earlier quoted context omitted.

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.

its not really a question of 'udp performs better'. in tcp we have to live to head-of-line blocking on losses and congestion control. if you don't care about receiving every packet, but only the most recent, then udp is a good choice. running without congestion control means that you avoid slowstart. but at a certain rate you run into poorly defined 'fairness' issues where you can easily negatively impact other flows…

[deleted]

Re: Why does SSH send 100 packets per keystroke?

#63

Post by simplicio »

dathinab wrote: post #10

> Keystroke obfuscation can be disabled client-side. please never do that (in production) if anyone half way serious tries they _will_ be able to break you encryption end find what you typed this isn't a hypothetical niche case obfuscation mechanism, it's a people broke SSH then a fix was found case. I don't even know why you can disable it tbh.

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.

Re: Why does SSH send 100 packets per keystroke?

#64

Post by observationist »

snowmobile wrote: post #2

> That 20ms is a smoking gun - it lines up perfectly with the mysterious pattern we saw earlier! Speaking of smoking guns, anybody else reckon Claude overuses that term a lot? Seems anytime I give it some debugging question, it'll claim some random thing like a version number or whatever, is a "smoking gun"

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?

Re: Why does SSH send 100 packets per keystroke?

#65

Post by nurettin »

snowmobile wrote: post #2

> That 20ms is a smoking gun - it lines up perfectly with the mysterious pattern we saw earlier! Speaking of smoking guns, anybody else reckon Claude overuses that term a lot? Seems anytime I give it some debugging question, it'll claim some random thing like a version number or whatever, is a "smoking gun"

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

Re: Why does SSH send 100 packets per keystroke?

#66

Post by lokar »

PaulHoule wrote: post #37

I find it disturbing. One thing you notice if you have ADSL is that some services are built as if slower connections matter and others are not. Like Google's voice and audio chat services work poorly but most of the others work well. Uploading images to Mastodon, Bluesky, Facebook, LinkedIn, Instagram and Nextdoor is reliable, but for Tumblr you have to try it twice. I don't what they are doing wrong but they are doi…

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.

Re: Why does SSH send 100 packets per keystroke?

#67

Post by MonkeyClub »

dave78 wrote: post #18
yread wrote: post #9

Earlier quoted context omitted.

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

Same with Gemini.

You can absolutely see this pattern in Gemini in 2026.

Btw, is the injection of "absolutely" and "in $YEAR" prevalent in other LLMs as well, or is it just in Gemini's dialect?

Re: Why does SSH send 100 packets per keystroke?

#68

Post by bergen »

PaulHoule wrote: post #37

I find it disturbing. One thing you notice if you have ADSL is that some services are built as if slower connections matter and others are not. Like Google's voice and audio chat services work poorly but most of the others work well. Uploading images to Mastodon, Bluesky, Facebook, LinkedIn, Instagram and Nextdoor is reliable, but for Tumblr you have to try it twice. I don't what they are doing wrong but they are doi…

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

Re: Why does SSH send 100 packets per keystroke?

#69

Post by cristoperb »

MonkeyClub wrote: post #67
dave78 wrote: post #18

Earlier quoted context omitted.

Same with Gemini.

You can absolutely see this pattern in Gemini in 2026. Btw, is the injection of "absolutely" and "in $YEAR" prevalent in other LLMs as well, or is it just in Gemini's dialect?

It's just Gemini. I'm guessing they changes the system prompt for the new year or something, but it's pretty annoying.

Re: Why does SSH send 100 packets per keystroke?

#70

Post by bot403 »

simplicio wrote: post #63
dathinab wrote: post #10

> Keystroke obfuscation can be disabled client-side. please never do that (in production) if anyone half way serious tries they _will_ be able to break you encryption end find what you typed this isn't a hypothetical niche case obfuscation mechanism, it's a people broke SSH then a fix was found case. I don't even know why you can disable it tbh.

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.

I'm just guessing but this chaff sounds like it wouldn't actually change the latency or delivery of your actual keystrokes while buffering or jitter would.

So the "real" keystrokes are 100% the same but the fake ones which are never seen except as network packets are what is randomized.

It's actually really clever.

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