To generate public (e,n) key from the private key using openssl you can use the following command: openssl rsa -in private.pem -out public.pem -pubout To dissect the contents of the private.pem private RSA key generated by the openssl command above run the following (output truncated to labels here).
Aug 19, 2019 1. Start by logging into the source machine (local server) and creating a 2048-bit RSA key pair using the command. Ssh-keygen -t rsa. If you want to tighten up security measures, you can create a 4096-bit key by adding the -b 4096 flag. Ssh-keygen -t rsa -b 4096. How to Generate SSH Public/Private Keys on Windows By Alexandru Andrei – Posted on Sep 17, 2019 Sep 17, 2019 in Windows If you ever managed a Linux server from Windows, you probably used PuTTY or at least heard about it. To generate these keys, simply type ssh-keygen -t rsa -b 2048 and follow the prompts. To install the keys to the default location, just press enter when prompted for a file name. We strongly encourage the use of a passphrase. Some machines may put these files in a different spot. How can I find the private key for my SSL certificate. If you just got an issued SSL certificate and are having a hard time finding the corresponding private key, this article can help you to find that one and only key for your certificate. Sep 26, 2019 Open the PuTTYgen program. For Type of key to generate, select SSH-2 RSA. Click the Generate button. Move your mouse in the area below the progress bar.
This article covers a version of Ubuntu that is no longer supported. If you are currently operate a server running Ubuntu 12.04, we highly recommend upgrading or migrating to a supported version of Ubuntu:
Reason:Ubuntu 12.04 reached end of life (EOL) on April 28, 2017 and no longer receives security patches or updates. This guide is no longer maintained.
See Instead:
This guide might still be useful as a reference, but may not work on other Ubuntu releases. If available, we strongly recommend using a guide written for the version of Ubuntu you are using. You can use the search functionality at the top of the page to find a more recent version.
When configuring a large amount of servers that have many users, keeping SSH access in line for your infrastructure can get complicated. There are quite a few ways of implementing a centralized authentication authority, such as LDAP, but these are sometimes overkill.
SSH actually has the functionality to use a certificate authority to authenticate servers and clients. This works both ways. Using this system, you can authenticate a host to a client, avoiding confusing messages about being unable to validate the authenticity of the host. You can also validate the client to the host, allowing you to register a new SSH key in one place and allow access across your organization.
We’ll discuss how to leverage these certificates in both of the ways discussed above. We’ll be demoing this on three Ubuntu 12.04 VPS instances. One will serve as the host, another as the client, and the third will function as the certificate authority.
We will start by configuring certificates that will authenticate our servers to our clients. This will allow our clients to connect to our servers without needing to question the authenticity of the server.
We begin on the machine that we will be using as the certificate authority. In this example, we’ll refer to this as “auth.example.com”.
First, we need to generate some RSA keys that will function as the signing keys. Use any user you’d like, but the root user is probably a good idea. We will be creating keys called “server_ca” and “server_ca.pub” since these will be used to authenticate our servers.
Generate ethereum private key javascript. 2019-11-10 I need to generate Ethereum wallets for each user of my site. I need to get private and public keys. How to do it using PHP or Javascript? For Ethereum I found web3.js library which I can use for getting access to an ethereum nodes, but I see examples only for checking balances or sending transactions for existed wallets.
Let’s create these keys in our home directory:
You will be asked if you’d like to create a passphrase. This will add an additional layer of protection to your key in the event that it falls into the wrong hands. Once this is finished, you’ll have a private and public key in your home directory:
Now that we have our keys, we can begin signing our host keys.
We should start by signing the host key of the certificate authority itself. We can do this using the following syntax:
Let’s go over what all of this means.
Afterwards we specify the key that we want to sign.
In our case, to sign our own host RSA key, we will use a line that looks like this. We are going to identify this server as “host_auth_server”. We will be prompted for the passphrase we used when creating the signing key:
As you can see from the output, our certificate is valid for one year. It has been created in the same directory as our server host key (/etc/ssh/) and is called “ssh_host_rsa_key-cert.pub”.
Now that we have signed our host key on the certificate authority itself, we can sign the host key for the separate SSH server we’re trying to authenticate to clients.
Copy the host key from our SSH server. We’ll refer to this machine as “sshserver.example.com”. You can do this using scp:
Now, we can create a certificate from this file using the same method we used above. We’ll need to change some values to refer to the new host we’re signing:
Now, we need to copy the generated certificate file back onto the host. Again, we can use scp for this:
Afterwards, we can delete both the SSH server’s public key and certificate from our authentication server:
We now have the signed certificates in place, we just need to configure our components to use them.
First, we need to continue with both of our servers (auth.example.com and sshserver.example.com) to make them aware of the certificate files we created.
On both of these machines, we’ll have to edit the main SSH daemon configuration file. Make sure you are editing the sshd_config file, not the ssh_config file:
If you can find a HostCertificate line, modify it. Otherwise, add this to the bottom of the file. We need to establish to path to our host certificate file:
Save and close the file when you are finished.
Now, restart the SSH daemon to make these changes happen:
Do this on all of the servers you are configuring host certificates for.
Now, our servers are configured to use the certificate, but our client does not know how to check the certificate that the server will present.
On our client machine, which we’ll be referring to as “client.example.com”, open or create the “~/.ssh/known_hosts” file:
We need to remove any entries that have to do with the servers we’re configuring for certificate entry. It may be best to delete everything.
Afterwards, we need to add a special entry that specifies the public key that we should use to check the certificate that our hosts will give us during login. Start it off with @cert-authority. Afterwards, it can include a domain restriction where the key will be applied, followed by the public certificate authority key that we’ve been signing everything with.
On your certificate authority machine, you can get the public certificate signing key by typing:
Using this information, the line in your ~/.ssh/known_hosts file should look like:
Save and close the file when you’re done.
Now, when you visit the SSH server for the first time from your client (using the full hostname), you should not be asked whether you trust the remote host. This is because the host has presented its host certificate to you, signed by the certificate authority. You’ve checked your known_hosts file and verified that the certificate is legitimate.
Now that we’ve learned how to authenticate servers to our users, we can also configure our certificate authority to authenticate our users to our servers.
As before, this process will start on our certificate authority server. We will need to generate a new set of keys, this time, to sign user certificates:
Again, select a passphrase so that your key will be protected if someone gains access.
When you are done, you will need to copy the public key onto each of your SSH servers that need to validate user authenticity. We will do this using scp as usual:
We need to modify our SSH daemon configuration on our SSH server to look for this key.
On our “sshserver.example.com” host, open the configuration file:
At the bottom, below our HostCertificate line, we need to add another line that references the file we just copied over:
Again, we’ll need to restart the SSH daemon for these changes to take place:
Now that the servers are configured to trust keys signed by the users_ca key, we need to actually sign the users’ authentication keys so that this scheme will work.
First, we need to get our client key onto the certificate authority server with scp. From the cert server, type:
Now that we have the key on the cert machine, we can sign it using our users_ca key. This will be very similar to last time we signed keys using the server_ca keys, only now, we don’t include the -h parameter, because these are user keys.
The command we want is something like this. Change the “username” value to reflect the name of the user you’re signing for easier management:
You will be prompted for the users_ca passphrase that set during the key’s creation. Now, we have an id_rsa-cert.pub file in our directory that we need to transfer back onto our client machine:
Now, when you log into sshserver.example.com from your client computer, you should not be asked for your authentication details, even if you’ve never before logged into this server as this user.
By signing your host and user keys, you can create a more flexible system for user and server validation. This allows you to set up one centralized authority for your entire infrastructure, in order to validate your servers to your user, and your users to your servers.
While perhaps not the most powerful way of creating centralized authentication, it is easy to set up and leverages existing tools without requiring a lot of time and configuration. It also has the advantage of not requiring the CA server to be online to check the certificates.
Contents
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Parent page: Internet and Networking >> SSH
Public key authentication is more secure than password authentication. This is particularly important if the computer is visible on the internet. If you don't think it's important, try logging the login attempts you get for the next week. My computer - a perfectly ordinary desktop PC - had over 4,000 attempts to guess my password and almost 2,500 break-in attempts in the last week alone.
With public key authentication, the authenticating entity has a public key and a private key. Each key is a large number with special mathematical properties. The private key is kept on the computer you log in from, while the public key is stored on the .ssh/authorized_keys file on all the computers you want to log in to. When you log in to a computer, the SSH server uses the public key to 'lock' messages in a way that can only be 'unlocked' by your private key - this means that even the most resourceful attacker can't snoop on, or interfere with, your session. As an extra security measure, most SSH programs store the private key in a passphrase-protected format, so that if your computer is stolen or broken in to, you should have enough time to disable your old public key before they break the passphrase and start using your key. Wikipedia has a more detailed explanation of how keys work.
Public key authentication is a much better solution than passwords for most people. In fact, if you don't mind leaving a private key unprotected on your hard disk, you can even use keys to do secure automatic log-ins - as part of a network backup, for example. Different SSH programs generate public keys in different ways, but they all generate public keys in a similar format:
Key-based authentication is the most secure of several modes of authentication usable with OpenSSH, such as plain password and Kerberos tickets. Key-based authentication has several advantages over password authentication, for example the key values are significantly more difficult to brute-force, or guess than plain passwords, provided an ample key length. Other authentication methods are only used in very specific situations.
SSH can use either 'RSA' (Rivest-Shamir-Adleman) or 'DSA' ('Digital Signature Algorithm') keys. Both of these were considered state-of-the-art algorithms when SSH was invented, but DSA has come to be seen as less secure in recent years. RSA is the only recommended choice for new keys, so this guide uses 'RSA key' and 'SSH key' interchangeably.
Key-based authentication uses two keys, one 'public' key that anyone is allowed to see, and another 'private' key that only the owner is allowed to see. To securely communicate using key-based authentication, one needs to create a key pair, securely store the private key on the computer one wants to log in from, and store the public key on the computer one wants to log in to.
Using key based logins with ssh is generally considered more secure than using plain password logins. This section of the guide will explain the process of generating a set of public/private RSA keys, and using them for logging into your Ubuntu computer(s) via OpenSSH.
The first step involves creating a set of RSA keys for use in authentication.
This should be done on the client.
To create your public and private SSH keys on the command-line:
You will be prompted for a location to save the keys, and a passphrase for the keys. This passphrase will protect your private key while it's stored on the hard drive:
Your public key is now available as .ssh/id_rsa.pub in your home folder.
Congratulations! You now have a set of keys. Now it's time to make your systems allow you to login with them
You need to change all your locks if your RSA key is stolen. Otherwise the thief could impersonate you wherever you authenticate with that key.
An SSH key passphrase is a secondary form of security that gives you a little time when your keys are stolen. If your RSA key has a strong passphrase, it might take your attacker a few hours to guess by brute force. That extra time should be enough to log in to any computers you have an account on, delete your old key from the .ssh/authorized_keys file, and add a new key.
Your SSH key passphrase is only used to protect your private key from thieves. It's never transmitted over the Internet, and the strength of your key has nothing to do with the strength of your passphrase.
The decision to protect your key with a passphrase involves convenience x security. Note that if you protect your key with a passphrase, then when you type the passphrase to unlock it, your local computer will generally leave the key unlocked for a time. So if you use the key multiple times without logging out of your local account in the meantime, you will probably only have to type the passphrase once.
If you do adopt a passphrase, pick a strong one and store it securely in a password manager. You may also write it down on a piece of paper and keep it in a secure place. If you choose not to protect the key with a passphrase, then just press the return when ssh-keygen asks.
Note: The default is a 2048 bit key. You can increase this to 4096 bits with the -b flag (Increasing the bits makes it harder to crack the key by brute force methods).
The main problem with public key authentication is that you need a secure way of getting the public key onto a computer before you can log in with it. If you will only ever use an SSH key to log in to your own computer from a few other computers (such as logging in to your PC from your laptop), you should copy your SSH keys over on a memory stick, and disable password authentication altogether. If you would like to log in from other computers from time to time (such as a friend's PC), make sure you have a strong password.
The key you need to transfer to the host is the public one. If you can log in to a computer over SSH using a password, you can transfer your RSA key by doing the following from your own computer:
Where <username> and <host> should be replaced by your username and the name of the computer you're transferring your key to.
Due to this bug, you cannot specify a port other than the standard port 22. You can work around this by issuing the command like this: ssh-copy-id '<username>@<host> -p <port_nr>'. If you are using the standard port 22, you can ignore this tip.
Another alternative is to copy the public key file to the server and concatenate it onto the authorized_keys file manually. It is wise to back that up first:
You can make sure this worked by doing:
You should be prompted for the passphrase for your key:
Enter passphrase for key '/home/<user>/.ssh/id_rsa': |
Enter your passphrase, and provided host is configured to allow key-based logins, you should then be logged in as usual.
If you have an encrypted home directory, SSH cannot access your authorized_keys file because it is inside your encrypted home directory and won't be available until after you are authenticated. Therefore, SSH will default to password authentication.
To solve this, create a folder outside your home named /etc/ssh/<username> (replace '<username>' with your actual username). This directory should have 755 permissions and be owned by the user. Move the authorized_keys file into it. The authorized_keys file should have 644 permissions and be owned by the user.
Then edit your /etc/ssh/sshd_config and add:
Finally, restart ssh with:
The next time you connect with SSH you should not have to enter your password.
If you are not prompted for the passphrase, and instead get just the
prompt as usual with password logins, then read on. There are a few things which could prevent this from working as easily as demonstrated above. On default Ubuntu installs however, the above examples should work. If not, then check the following condition, as it is the most frequent cause:
On the host computer, ensure that the /etc/ssh/sshd_config contains the following lines, and that they are uncommented;
If not, add them, or uncomment them, restart OpenSSH, and try logging in again. If you get the passphrase prompt now, then congratulations, you're logging in with a key!
If you're sure you've correctly configured sshd_config, copied your ID, and have your private key in the .ssh directory, and still getting this error:
Permission denied (publickey). |
Chances are, your /home/<user> or ~/.ssh/authorized_keys permissions are too open by OpenSSH standards. You can get rid of this problem by issuing the following commands:
This error occurs when the ssh-agent on the client is not yet managing the key. Issue the following commands to fix:
This command should be entered after you have copied your public key to the host computer.
The permissions of files and folders is crucial to this working. You can get debugging information from both the client and server.
if you think you have set it up correctly , yet still get asked for the password, try starting the server with debugging output to the terminal.
To connect and send information to the client terminal
No matter how your public key was generated, you can add it to your Ubuntu system by opening the file .ssh/authorized_keys in your favourite text editor and adding the key to the bottom of the file. You can also limit the SSH features that the key can use, such as disallowing port-forwarding or only allowing a specific command to be run. This is done by adding 'options' before the SSH key, on the same line in the authorized_keys file. For example, if you maintain a CVS repository, you could add a line like this:
When the user with the specified key logged in, the server would automatically run /usr/bin/cvs server, ignoring any requests from the client to run another command such as a shell. For more information, see the sshd man page. /755