To create a remote session, you specify the target computer with the HostName parameter and provide the user name with UserName. When running the cmdlets interactively, you're prompted for a password. You can also use SSH key authentication using a private key file with the KeyFilePath parameter. Ssh client can use many authentication methods like password, keys. On a server, I set password-less log in with private/public key. Now, I want to try whether the new password is set correctly by log on using ssh. The sshpass utility is designed to run SSH using the keyboard-interactive password authentication mode, but in a non-interactive way. SSH uses direct TTY access to ensure that the password is indeed issued by an interactive keyboard user. Sshpass runs SSH in a dedicated TTY, fooling SSH into thinking it is getting the password from an.

The ssh program on Linux allows you to specify a program or script from where it should get a passphrase when it needs one. This allows you to, for instance, hookup it up to your password manager to feed it the passphrase. You can do this by specifying the path to the program to execute in the SSH_ASKPASS environment variable.

I use the pass password manager (which installs the pass command). Check it out, it’s pretty awesome. Here’s how to hook up pass to ssh:

First, create a simple bash script to feed pass the path to the password in my password store that I want it to display (let’s say I save it in ~/ssh-pass-passphrase.sh and forward the input to it):

Then, make sure your user is the only one allowed to edit the script:

Now set the SSH_ASKPASS environment variable:

You should now be able to use it with any ssh command that needs a passphrase (e.g ssh-add) like this:

Please note that this will not work if the ssh command is called directly on the terminal (is attached to a terminal). A workaround is to call it after a pipe. In the command above, I’ve used the pipe to pass the path to the passphrase in pass to ssh-add. ssh-add will eventually call ~/ssh-pass-passphrase.sh and provide the path when read is fired in the script.

Here’s text from the ssh manual detailing what SSH_ASKPASS does:

If ssh needs a passphrase, it will read the passphrase from the current terminal if it was run from a terminal. If ssh does not have a terminal associated with it but DISPLAY and SSH_ASKPASS are set, it will execute the program specified by SSH_ASKPASS and open an X11 window to read the passphrase. This is particularly useful when calling ssh from a .xsession or related script. (Note that on some machines it may be necessary to redirect the input from /dev/null to make this work.)

Using an ssh-agent, or how to type your ssh password once, safely.

If you work a lot on linux and use ssh often, you quicklyrealize that typing your password every time you connect to a remotehost gets annoying.

Not only that, it is not the best solution in terms of security either:

• Every time you type a password, a snooper has an extra chance to see it.
• Every host you ssh to with which you use your password, well, has to know your password. Or a hash of your password. In any case, you probably have typed your password on that host once or twice in your life (even if just for passwd, for example).
• If you are victim of a Man In The Middle attack, your password may get stolen. Sure, you can verify the fingerprint of every host you connect to, and disable authentication without challenge and response in your ssh config. But what if there was a way you didn't have to do that?

This is where key authentication comes into play: instead of using a passwordto log in a remote host, you can use a pair of keys, and well, ssh-agent.

Using ssh keys

All you have to do is: Docker on raspberry.

1. generate a pair of keys with ssh-keygen. This will create two files: a public key (normally .pub), and a private key. The private key is normally kept encrypted on disk. After all, it's well, supposed to be private. ssh-keygen will ask you to insert a password. Note that this password will be used to decrypt this file from your local disk, and never sent to anyone. And again, as the name suggest, you should never ever disclose your private key.

2. copy your public key into any system you need to have access to. You can use rsync, scp, type it manually, or well, use the tool provided with openssh: ssh-copy-id. Note that you could even publish your public key online: there is no (known) way to go from a public key to your private key and to get access to any of your systems. And if there was a way, well, public key encryption would be dead, and your bank account likely empty.

and .. done! That's it, really, just try it out:

So.. what are the advantages of using keys? There are many:

1. Your passphrase never leaves your local machine. Which generally makes it harder to steal.
2. You don't have a password to remember for each different host. Or..
3. .. you don't have the same password for all hosts you connect to (depending on your password management philosophies).
4. If somebody steals your passphrase, there's not much he can do without your private key.
5. If you fear somebody has seen your passphrase, you can change it easily. Once. And for all.
6. If there is a 'man in the middle', he may be able to hijack your session. Once (and well, feast on your machine, but that's another story). If a 'man in the middle' got hold of your password instead, he could enjoy your machine later, more stealthy, for longer, and may be able to use your password on other machines.
7. They just work. Transparently, most of the times. With git, rsync, scp, and all their friends.
8. You can use an agent to make your life happier and easier.

And if you're wondering what an agent is, you can go to the next section.

Your agent friend

Ok. So you have read this much of the article, and still we have not solved theproblem of having to type your password every freaking time, have we?

That's where an agent comes in handy. Think of it as a safe box you have tostart in the background that holds your keys, ready to be used.

You start an ssh-agent by running something like:

in your shell. You can then feed it keys, with ssh-add like:

or, if your key is in the default location, you can just:

ssh-add will ask your passphrase, and store your private key into thessh-agent you started earlier. ssh, and all its friends (including git,rsync, scp..) will just magically use your agent friend when you try tossh somewhere. Convenient, isn't it?

Assuming you added all the keys you need, you can now ssh to any host,as many times as you like, without ever ever having to retype your password.

Not only that, but you can exploit agent forwarding to jump from one hostto another seamlessly.

Let me give you an example:

• Let's say you have to connect to a server at your office.
• Let's say this server is firewalled. In order to ssh there, you first need to ssh into another gateway. Sounds familiar, doesn't it? This means you end up doing:

On this second ssh, what happens? Well, if you type your password, yourcleartext password is visible to the gateway. Yes, it is sent encrypted,decrypted, and then through the console driver fed to the ssh process.If a keylogger was running, your password would be lost.

Worst: we are back to our original problem, we have to type our passwordmultiple times!

We could, of course, store our private key on the company gateway and runan agent there. But that would not be a good idea, would it? Remember:your private key never leaves your private computer, you don't wantto store it on a remote server.

So, here's a fancy feature of ssh and ssh-agent: agent forwarding.

On many linux systems, it is enabled by default: but if you pass -A tothe first ssh command (or the second, or the third, ..), ssh willensure that your agent running on your local machine is usable from theremote machine as well.

For example:

The second ssh here, run from the company gateway, will not ask youfor a password. Instead, it will detect the presence of a remote agent,and use your private key instead, and ask for no password.

Sounds dangerous? Well, there are some risks associated with it, whichwe'll discuss in another article. But here is the beauty of the agent:

Your private key never leaves your local computer. That's right.By design, the agent never ever discloses your private key, itnever ever hands it over to a remote ssh or similar. Instead,ssh is designed such as when an agent is detected, the informationthat needs to be encrypted or verified through the agent is forwardedto the agent. That's why it is called agent forwarding, andthat's why it is considered a safer option.

Configuring all of this on your machine

So, let's summarize the steps:

1. Generate a set of keys, with ssh-keygen.
2. Install your keys on remote servers, with ssh-copy-id.
3. Start an ssh-agent to use on your machine, with eval ssh-agent.
4. ssh-add your key, type your password once.
5. Profit! You can now ssh to any host that has your public key without having to enter a password, and use ssh -A to forward your agent.

Easy, isn't it? Where people generally have problems is on how andwhere to start the ssh-agent, and when and how to start ssh-add.

The long running advice has been to start ssh-agent from your .bashrc,and run ssh-add similarly.

In today's world, most distributions (including Debian and derivatives),just start an ssh-agent when you first login. So, you really don't haveanything to do, except run ssh-add when you need your keys loaded,and be done with it.

Still many people have snippets to the extent of:

in their .bashrc, which basically says 'is there an ssh-agent already running? no? start one, and add my keys'.

Ubiquiti Ssh Password

This is still very annoying: for each console or each session you login into, youend up with a new ssh-agent. Worse: this agent will run forever with your privatekeys loaded! Even long after you logged out. Nothing and nobody will ever kill your agent.

So, your three lines of .bashrc snippet soon becomes 10 lines (to cache agents on disk),then it breaks the first time you use NFS or any other technology to share your homedirectory, and then.. more lines to load only some keys, some magic in .bash_logout tokill your agent, and your 4 lines of simple .bashrc get out of control

Conclusion

I promised myself to talk about the pitfalls of using an agent and common approachesto solving the most common problems in a dedicated article. My suggestion for now?

• Use the ssh-agent tied with your session, and managed by your distro, when one is available (just try ssh-add and see if it works!).

• Use -t to ssh-add and ssh-agent, so your private key is kept in the agent for a limited amount of time. One hour? 5 miutes? you pick. But at the end of that time, your key is gone.

• Use something like ssh-ident, to automatically maintain one or more agents, and load ssh keys on demand, so you don't even have to worry about ssh-add.

1password Ssh Keys

For full disclosure, I wrote ssh-ident. Surprisingly, that still doesn't preventme from liking it.