What is the randomart image for?

https://bytes.zone/posts/what-is-the-randomart-image-for/

by susam • 3 years ago

158 44 3 years ago

graderjs• 3 years ago

I loved this!

Thank you for this:

and it turns out it worked! For example, I've started seeing the GitHub fingerprint (above) as something like the Statue of Liberty if it were a cat (don't ask why; that's just how my brain sees it)

Lol I’m switching this thing on!

folli2• 3 years ago

Tangentially related: does any one know any nice libraries/tools to generate images (PNGs or whatever, doesn't need to be terminal compatible, colors even preferred) from hashes?

isoprophlex• 3 years ago

You're looking for an Identicon, probably

https://en.m.wikipedia.org/wiki/Identicon

See some github repos:

https://github.com/topics/identicon-generator

folli2• 3 years ago

Right on, that's very close to what I'm looking for! Thanks!

3-cheese-sundae• 3 years ago

I know of robohash: https://robohash.org

kaoD• 3 years ago

and see if I started to be able to recognize the randomart images in the way the manual implies I'd be able to, and it turns out it worked!

How computationally expensive is it to generate a key with randomart that kinda-resembles a known randomart?

I've always ignored randomart since I always assumed it's easy to get a close-enough "collision".

EDIT: algorithm explained here https://pthree.org/2013/05/30/openssh-keys-and-the-drunken-b...

eat_veggies• 3 years ago

Seems to be pretty doable ("collisions" in the last section): https://blog.benjojo.co.uk/post/ssh-randomart-how-does-it-wo...

Drakim• 3 years ago

The same question goes for how computationally expensive it is to generate a key that kinda-resembles a known key? If you are just eyeballing the key "yeah that looks like Github's key" when the terminal ask you, you might fall for a fake one that merely begins with the same characters.

The neat trick is that it's others of magnitude harder to find a key that kinda-resembles a known key and kinda-resmbles it's randomart, so if both are presented at the same time, you'd be safer.

RamRodification• 3 years ago

All in all, I think I'd recommend doing this. Even if the keys never change, it's pleasing to see the art show up in your terminal.

If someone uses "the keys never change" as an argument against this, I think they have completely missed the point. (Not saying OP has).

cmeacham98• 3 years ago

The real argument is that if the keys change, you'll know about it, because OpenSSH will yell very loudly about it.

The random art is intended for _first time_ connections, where OpenSSH has to trust your judgement of the key's legitimacy because it has never connected to that host before.

It's not like it will hurt anything, but turning it on for every connection doesn't make a security difference.

xp84• 3 years ago

yeah, i guess syncing around your known_hosts file to everyplace you originate an ssh connection from, would make more of a difference. So that way you minimize the making of first-time connections as much as possible.

jrm4• 3 years ago

I always understood the option, but seems like a little color would go a LONG way in making them much more usable? I never got around to paying attention to them and I think that's why.

csears• 3 years ago

Is it safe to publicly post the randomart visualization of keys like this?

demodifier• 3 years ago

Good question. I would assume that with the visualization being defined by the public-key of the server, this cannot be use to reverse-engineer the private key. Also, the linked paper (I just read the summary) does try to attempt this and partially succeeds and talks more about the implication.

coldpie5• 3 years ago

I think you should treat it as posting the key itself. In other words, it's probably possible to transform from the randart back to the key (else it wouldn't be unique per key, right?). So for a public key that is intended to be public, yes, it should be fine. For keys which you do not want public, it's probably not a good idea to post it publicly.

duskwuff2• 3 years ago

It's not even a representation of the public key itself; it's the SHA256 fingerprint of the key. There's no practical way to transform that back into the key -- and, in any case, the server will send that key to any client that connects, so it's not like recovering it from a screenshot accomplishes anything.

benjojo12• 3 years ago

Yes, Not only is it a visualisation of a SHA256 hash of the public key, but it's hard to turn the visualisation back into a SHA256 hash itself.

jhbadger• 3 years ago

Maybe they could use something like Chernoff faces (a method in which data is converted into images of a human face on the grounds that people are better at distinguishing faces than other images).

https://en.wikipedia.org/wiki/Chernoff_face

dark-star• 3 years ago

How much of a face would you recognize if it is rendered with ASCII on a console though? Which is probably the default use-case for SSH for 99% of people.

Darkphibre2• 3 years ago

Heh... as someone with prosopagnosia, this wouldn't help too much. But I agree it'd help most people!!

comefho• 3 years ago

What's the point when the server, if it's one you're logging into regularly (or even just more than once), will already be in your known_hosts file? Let the computer do the checking for you.

coldpie5• 3 years ago

Good question. Perhaps it's useful if you're logging in from many machines/users without populated known_hosts? So if you spin up a new machine and push to Github, you can recognize it visually by its randart which you saw many times before on other machines.

Eduard• 3 years ago

Showing the random art can help to notice if you connected to the wrong server by accident, e.g. Incorrectly connecting to staging.example.com when you actually wanted to connect to live.example.com

vmoore• 3 years ago

Needs this for SHA256 sums

I often compare SHA256 sums of software and have to trust my eyes that the two hashes are the same. Most of the time I just look at the first 5 characters, alongside the last five characters, but I don't look at the middle, and I really should.

Some hashes could deliberately look the same but have 2-3 characters different, and I wouldn't know, unless I look at each character individually, but who does that?

coldpie5• 3 years ago

It is a bit of effort, but you can make the computer do the verification for you by writing (or generating) a simple text file. Using Perl shasum because I'm on a mac at the moment, but Linux sha256sum works the same:

    $ echo hi > some_file
    $ shasum -a 256 some_file > check
    $ cat check
    98ea6e4f216f2fb4b69fff9b3a44842c38686ca685f3f55dc48c5d3fb1107be4  some_file
    $ shasum -a 256 -c check
    some_file: OK
    $ echo $?
    0
    $ echo bye > some_file
    $ shasum -a 256 -c check
    some_file: FAILED
    shasum: WARNING: 1 computed checksum did NOT match
    $ echo $?
    1

Edit: Oh cool, at least perl's shasum allows reading from stdin so you can even skip the file if you're just copying some check file off the software's website:

    $ shasum -a 256 -c - <<EOF
    > 98ea6e4f216f2fb4b69fff9b3a44842c38686ca685f3f55dc48c5d3fb1107be4  some_file
    > EOF
    some_file: OK

radlad• 3 years ago

Something like this also works:

    hash="4e575a5ee4af2925477c9eea887ff560d23a586dbaf90b616d26c47ec429ca13"
    [[ "$hash" == "$(shasum -a 256 file | awk '{print $1 }')" ]] && echo "Valid" || echo "Invalid checksum"

I use that little if-statement in some build systems.

jpdaigle• 3 years ago

Any hash calculations using a "read from stdin or a pipe" strategy, in my experience, is fraught with issues caused by an extra newline at the end of the input possibly being there today, and not in later checks, or vice-versa.

When people claim they wrote a prediction at some later date, they always have to document the EXACT command used to avoid this, e.g. `echo "smart prediction" | md5sum`

remram2• 3 years ago

It is weird that this doesn't exist. The algorithm is pretty simple and there are libraries for it, but I couldn't find a generic command-line tool that shows one after hashing any file.

This might be a cool contribution to coreutils (which contains the `sha256sum`, `sha1sum`, `md5sum`, ... programs)

refuse• 3 years ago

I'm asking this in the wrong place, but does anyone know why coreutils doesn't include sha3 or derivatives?

r1ch• 3 years ago

Malware that replaces crypto addresses on webpages is already aware of this - they try to generate addresses with similar starting and ending characters since most people aren't checking the whole thing.

rzzzt• 3 years ago

There is one method that might help, the "astronomer's blink": open two editor tabs, paste the expected and the actual hash in either tab, then quickly switch between tabs using the keyboard (eg. Ctrl+PgUp/Dn if your editor supports this). Can also be used for comparing ordered JSON output when in a hurry.

(The term comes from https://en.wikipedia.org/wiki/Blink_comparator and someone wrote about this in a tech context as well, but I forgot where I read it. I'm seeing one search hit with the exact expression, so it could have been something close as well.)

Too• 3 years ago

If you are going to take the effort to paste into an editor you might as well paste both hashes into same tab, put the cursor on one and let the ide highlight all occurances. Ctrl-c + Ctrl-f for those with less sophisticated editors.

Heck, most editors even come with a “compare selection with clipboard” option.

saul_goodman• 3 years ago

In my head I've always read that as rando-mart. I have a mental image of a small high-density city street shop with anything you could possibly want to buy including small ascii art images of my ssh keys.

Joker_vD• 3 years ago

Reminds me of a slide from one of Peter Gutmann's lectures on PKI and related stuff: a mock up of a title page for a proposed conference paper, titled "Do SSH Fingerprints Increase Security?", with abstract consisting of just "No."

Yes, it follows other slides that describe precisely the attack in TFA, only for traditional SSH fingerprints, and the real world surveys on the "how many users have called or emailed to verify the SSH key fingerprint whenever the key changed?" question (answer: literally zero), so it seems sadly accurate.

syntheticcorp• 3 years ago

Found it, pg 47 https://www.cs.auckland.ac.nz/~pgut001/pubs/defending.pdf

2b3a51• 3 years ago

Slackware displays the randomart images for some kind of public key when you boot. I always wondered what these were, so thanks for posting.

lagniappe• 3 years ago

I just want a random art that has shallow minerals, low savagery, and a temperate climate.

DoItToMe81• 3 years ago

I want high savagery and lots of giant animals, so I don't have to rely on elves.

What is the randomart image for?

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