LinuxQuestions.org - Questions about SSH

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LinuxQuestions.org (/questions/)

- Linux - Newbie (https://www.linuxquestions.org/questions/linux-newbie-8/)

- - Questions about SSH (https://www.linuxquestions.org/questions/linux-newbie-8/questions-about-ssh-4175573213/)

RobInRockCity

02-26-2016 11:57 AM

Quote:

Originally Posted by lazydog (Post 5506575)

@OP: From what I have read the disconnect is between the keyboard and the seat. Not understanding how key-pairs work properly and what key you should be seeing. I would suggest you contact your hosting and work out your confusion with them. They can tell you exactly what you should be seeing.

If I thought my web host was able to competently help, I wouldn't be here...

RobInRockCity

02-26-2016 12:02 PM

Quote:

Originally Posted by cliffordw (Post 5506375)

You can see the server's key as a non-root user by running

Code:

ssh-keyscan localhost > /tmp/x && ssh-keygen -lf /tmp/x && rm /tmp/x

Can you explain what that code does and where I would run it? (Sorry, I'm not a system admin)

Quote:

Originally Posted by cliffordw (Post 5506375)

There is a server key, used by sshd to identify the server. Separate from that individual users can have user keys, which allows them to authenticate
without passwords.
The command above created a key pair for your user on the server. This is not the same thing as the server's host key. This key would only be of any use if you want to connect from the server to somewhere else, and plays no role at all in the connection from your laptop to the server.

So my web host gave me the wrong info...

Quote:

Originally Posted by cliffordw (Post 5506375)

This is where the confusion lies, yes. You're still off the mark, though ;-) The fingerprint you get asked to confirm is the HOST key, not the USER key.

You would not need their help to get the fingerprint for the key you generated anyway; simply run "ssh-keygen -lf ~/.ssh/id-rsa.pub" on your laptop for that.

What do I need to do to get a fingerprint that I can compare against the fingerprint I see when I first try to SSH in to my server?

Quote:

Originally Posted by cliffordw (Post 5506375)

Getting back to your real concern, I'd suggest you ask your hosting provider to send you a copy of the /etc/ssh/ssh_host_rsa_key.pub file. This should match the entry in your ~/.ssh/known_hosts file for that server.

Is it safe to do that via email?

Would I be giving away details of my server or keys that I shouldn't?

suicidaleggroll

02-26-2016 12:48 PM

Quote:

Originally Posted by RobInRockCity (Post 5506633)

What do I need to do to get a fingerprint that I can compare against the fingerprint I see when I first try to SSH in to my server?

That would the command cliffordw just gave you:

Code:

ssh-keyscan localhost > /tmp/x && ssh-keygen -lf /tmp/x && rm /tmp/x

Run it on the VPS, it will print out the fingerprint that you were shown, and accepted, when you first tried to ssh into the system.

If you want to know what it does, there are three parts:
1) ssh-keyscan localhost > /tmp/x
This dumps out the server key for the system on which you run the command into a file called "x" located in /tmp/. This would be the same as running "cp /etc/ssh/ssh_host_rsa_key.pub /tmp/x", which is the file I asked you to look at earlier and you just assumed you wouldn't be able to and didn't try...the public key files are world-readable, you don't need to be root.

2) ssh-keygen -lf /tmp/x
The -f flag tells it to read from the provided file, the -l flag tells it to print the fingerprint

3) rm /tmp/x
Cleans up the temporary file that you created with #1.

All of which could be shortened to simply:

Code:

ssh-keygen -lf /etc/ssh/ssh_host_rsa_key.pub

RobInRockCity

02-26-2016 02:32 PM

suicidaleggroll,

I was trying to follow your instructions, but I have the following issue in Terminal when I try to ssh into my VPS. Here is what is happening...

Code:

user1s-MacBook-Pro:~ user1$ ssh vps-user@111.222.333.44 -p 22



The authenticity of host '111.222.333.44' can't be established.

RSA key fingerprint is 3c:91:bb:81:ef:23:f1:b2:87:a5:2a:10:e8.



Are you sure you want to continue connecting (yes/no)? yes



Warning: Permanently added '111.222.333.44' (RSA) to the list of known hosts.



vps-user@111.222.333.44's password:

Why is it asking for a password?? The whole point of setting up a public/private key pair was so I just have to type in my passphrase on the private key, and NOT enter my cpanel password.

This is all very frustrating...

suicidaleggroll

02-26-2016 02:48 PM

Permissions are the usual cause.

On the remote server, run the following:

Code:

chmod 600 ~/.ssh/authorized_keys

chmod 700 ~/.ssh

chmod 750 ~

I'm assuming you already put your laptop's public key into ~/.ssh/authorized_keys on the server.

RobInRockCity

02-26-2016 05:52 PM

Quote:

Originally Posted by suicidaleggroll (Post 5506747)

Permissions are the usual cause.

On the remote server, run the following:

Code:

chmod 600 ~/.ssh/authorized_keys

chmod 700 ~/.ssh

chmod 750 ~

Dumb question, but how do I do that??

I have a VPS with CentOS6 and cPanel, but no Root access of my own. I thought the way I would execute your code above for the server key was supposed to be done after I SSH'ed into my VPS, but then I got that password issue.

So where and how do I run the chmod commands you recommend?

Quote:

Originally Posted by suicidaleggroll (Post 5506747)

I'm assuming you already put your laptop's public key into ~/.ssh/authorized_keys on the server.

No. I generated the key pair on my MacBook, and then I imported the public key into cPanel > Security > SSH Access > Manage Keys

So I can see my public key in cPanel, but I didn't do anything with ~/.ssh/authorized_keys

You'll have to help explain this to me as I learn all about Sys Admin stuff!

suicidaleggroll

02-26-2016 07:05 PM

I know nothing about cPanel, can't help you there.

You said you were prompted for a password, did you enter it? Do you know it?

RobInRockCity

02-26-2016 07:14 PM

Quote:

Originally Posted by suicidaleggroll (Post 5506867)

I know nothing about cPanel, can't help you there.

You said you were prompted for a password, did you enter it? Do you know it?

Yes, I know my cPanel password, but I didn't enter anything for fear my SSH connection is broken and a hacker might see it - or maybe I have already been hacked. :(

suicidaleggroll

02-26-2016 07:38 PM

The chances of that are incredibly low. Are you connecting using the domain name or IP address? If the IP, then the chances are practically non-existent.

RobInRockCity

02-26-2016 08:18 PM

Quote:

Originally Posted by suicidaleggroll (Post 5506882)

The chances of that are incredibly low. Are you connecting using the domain name or IP address? If the IP, then the chances are practically non-existent.

Think I am making some progress...

I took a chance and entered my password into SSH since my key pair stopped working.

At the command prompt on my server, I did this...

vps-user@111.222.333.44 [~}# ls

I see...

etc/
.ssh/

In etc/ is a directory called mydomain.com but there is nothing in it.

In .ssh/ I see...
authorized_keys
authorized_keys2
id_rsa.pub

I think this is one problem. Why do I have 2 authorized_key files?

I built a spreadsheet with two input fields (i.e. "Fingerprint from Web-Host" and "Fingerprint from Terminal") and created a formula to show MATCH/NO MATCH.

From there I went into TextWrangler and pasted the KEY from my MacBook's ~/.ssh/known_hosts file into "Fingerprint from Terminal".

Then I proceeded to run...

cat authorized_keys
cat authorized_keys2
cat id_rsa.pub

...and pasted the contents of each into the "Fingerprint from Web-Host" field. (In this case I am comparing KEYS and not fingerprints.)

There was NO MATCH in any of the three comparisons?!

So what is going on here???

suicidaleggroll

02-27-2016 07:56 AM

The fingerprint is not the public key. The fingerprint is calculated from the public key, and you've been given the command to do this calculation THREE TIMES already.

And as has already been explained to you, nothing you will find in ~/.ssh on the server has anything to do with this question, at all. The key you are looking for, the one that has to do with the server proving it is who it says it is, is in /etc/ssh.

pan64

02-27-2016 08:05 AM

authorized_keys2 is not used by default by any tool, it can only be a backup or something like that.

RobInRockCity

02-27-2016 10:56 AM

Quote:

Originally Posted by suicidaleggroll (Post 5507093)

The fingerprint is not the public key. The fingerprint is calculated from the public key,

When have I ever said that the keys were the fingerprint??

Quote:

Originally Posted by suicidaleggroll (Post 5507093)

and you've been given the command to do this calculation THREE TIMES already.

And I ran it.

Quote:

Originally Posted by suicidaleggroll (Post 5507093)

And as has already been explained to you, nothing you will find in ~/.ssh on the server has anything to do with this question, at all. The key you are looking for, the one that has to do with the server proving it is who it says it is, is in /etc/ssh.

Nothing personal, but the conversation would work better if people answered questions before moving on.

The conversation as evolved as I learn more, and I am taking people's advice and asking questions along the way to learn more.

RobInRockCity

02-27-2016 11:01 AM

Quote:

Originally Posted by cliffordw (Post 5506028)

Hi again,

As mentioned in your other question, this is the MD5 hash of the server's public key.

The server keys are usually in /etc/ssh/ssh_host_{dsa,rsa}. You can obtain the fingerprint by running:

Code:

ssh-keygen -lf /etc/ssh/ssh_host_rsa_key.pub

# and

ssh-keygen -lf /etc/ssh/ssh_host_dsa_key.pub

Which of these keys get used, and thus which fingerprint you get presented with, is determined by a negotiation between the client and server, depending on a number of configuration settings on both ends.

I ran this code - after spent Friday night trying to figure out how to do command line - and it worked.

What I don't understand is why I can't see this path in Terminal?

(I explained this in another post, but it seems like my questions and comments get skipped a lot.)

How can I run that command when there is no visiable directory structure or file there?

suicidaleggroll

02-27-2016 11:31 AM

Quote:

Originally Posted by RobInRockCity (Post 5507174)

When have I ever said that the keys were the fingerprint??

Sorry, I misread your post. I thought you were comparing the keys in authorized_keys, known_hosts, etc. to the fingerprint the web host sent you. I see now that is not the case.

Quote:

Originally Posted by RobInRockCity

What I don't understand is why I can't see this path in Terminal?

(I explained this in another post, but it seems like my questions and comments get skipped a lot.)

How can I run that command when there is no visiable directory structure or file there?

I just re-read the thread and I do not see where you asked this earlier. If I missed it I apologize, but I'm not seeing it anywhere.
That said, I don't understand the question. What can't you see in the terminal? There's no directory structure or file where? Best guess at interpreting your question is that you're confused about the difference between relative and absolute paths:
http://www.linuxnix.com/abslute-path...-in-linuxunix/

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