Keys are generally produced with auxiliary tools. Ssh-keygen is defacto tool used by ssh and other applications to create different type of keys. In this tutorial we will look how it works. Public Cryptography. Generating a SSH key pair. OpenSSH comes with a tool called ssh-keygen to generate key pairs. By default, it uses 2048-bit RSA keys, although this can be changed (more on that later). We will generate our first key pair with the command: ssh-keygen. When you run this command, it will ask you where you want to save the key. Generate an DSA SSH keypair with a 2048 bit private key. Ssh-keygen -t dsa -b 1024 -C 'DSA 1024 bit Keys' Generate an ECDSA SSH keypair with a 521 bit private key. Ssh-keygen -t ecdsa -b 521 -C 'ECDSA 521 bit Keys' Generate an ed25519 SSH keypair- this is a new algorithm added in OpenSSH. Ssh-keygen -t ed25519 Extracting the public key from an. Being a Sudo user, is it possible to create a SSH key for an user in the same Linux server? This Sudo user doesn't have a Switch user privilege. I have a server where I Login as sudo user say 'adm.
Ssh is a secure and popular protocol for managing different type of IT devices like Linux systems, Network devices etc. What makes ssh secure is the encryption of the network traffic. Network traffic is encrypted with different type of encryption algorithms. There is also user authentication done with encryption algorithms. These algorithms needs keys to operate. Keys are generally produced with auxiliary tools. ssh-keygen is defacto tool used by ssh and other applications to create different type of keys. In this tutorial we will look how it works.
Ssh-keygen Generate Server Keys 2017
We will look some terms and concepts about public cryptography in this part. In public cryptography there is two keys. These keys are called public and private. Public keys are known by others to create encrypted data. Private keys are only known by its owner. Data are encrypted by public keys by anyone but only the private key owner can decrypt the message. So keeping private key is important. ssh-keygen is used to create different type of public-private keys.
There are some configurations files those used by ssh. We will look the public private keys related configuration files.
~/.ssh/identity.pubcontains the protocol version 1 RSA public key~/.ssh/id_dsa contains the protocol version 2 DSA authentication identity of the user.~/.ssh/id_dsa.pub contains the protocol version 2 DSA public key for authentication~/.ssh/id_rsa contains the protocol version 2 RSA authentication identity of the user~/.ssh/id_rsa.pub contains the protocol version 2 RSA public key for authentication
Generating key without any parameter is very easy. This will generate with default values and options a key. This will take 3 step just enter after issuing the sshkeygen command.
Now we will specify the path key files to be saved. We do not enter a path if we want to use default path which is ~/.ssh/id_rsa
Now we will enter passphrase but we will not. Where our private key will
Again do not enter passphrase
In previous example we have generated ssh key with default settings. The default settings was like below.
- RSA
- 2048 bit
But we can specify the public key algorithm explicitly by using -t option like below.
DSA is less popular but useful public key algorithm. DSA keys can be generated by specifying key types with -t dsa
Keys have different size for different purposes. Bigger size means more security but brings more processing need which is a trade of. We can specify the size of the keys according to our needs with -s option and the length of key. The size count specifies bits in a key. So following example will create 1024 bit key.
Created keys will be written to the ~/.ssh with related name. This default behavior can be changed with -foption and file with path. In this example we will write keys to the current users home directory.
As we can see the path is not asked to us because we have all ready provided explicitly.
Private keys must be protected. There are different ways to protect privates. We should use symmetric cryptography to crypt private key. ssh-key all ready provide this feature. We will set password to access to the private key. In interactive run the passphrase is asked but we can also specify explicitly while calling command with -N option like below. We will provide passphrase in clear text. This passphrase also saved in bash history file which will create a security vulnerability. Keep these while using option based encryption of public keys.
Most authentication in Windows environments is done with a username-password pair.This works well for systems that share a common domain.When working across domains, such as between on-premise and cloud-hosted systems, it becomes more difficult.
By comparison, Linux environments commonly use public-key/private-key pairs to drive authentication.OpenSSH includes tools to help support this, specifically:
- ssh-keygen for generating secure keys
- ssh-agent and ssh-add for securely storing private keys
- scp and sftp to securely copy public key files during initial use of a server
This document provides an overview of how to use these tools on Windows to begin using key authentication with SSH.If you are unfamiliar with SSH key management, we strongly recommend you review NIST document IR 7966 titled 'Security of Interactive and Automated Access Management Using Secure Shell (SSH).'
Add the following line:Device=ANSI.SYSSave the file and start 'Command' (START = Run. = type 'command' and press 'Enter').Start the editor by typing 'edit' and press 'Enter'.See the following link to view all ANSI commands and how to use them. What key combination generates a backspace character in cmd.
About key pairs
Key pairs refer to the public and private key files that are used by certain authentication protocols.
SSH public-key authentication uses asymmetric cryptographic algorithms to generate two key files – one 'private' and the other 'public'. The private key files are the equivalent of a password, and should protected under all circumstances. If someone acquires your private key, they can log in as you to any SSH server you have access to. The public key is what is placed on the SSH server, and may be shared without compromising the private key.
When using key authentication with an SSH server, the SSH server and client compare the public key for username provided against the private key. If the public key cannot be validated against the client-side private key, authentication fails.
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Multi-factor authentication may be implemented with key pairs by requiring that a passphrase be supplied when the key pair is generated (see key generation below).During authentication the user is prompted for the passphrase, which is used along with the presence of the private key on the SSH client to authenticate the user.
Host key generation
Public keys have specific ACL requirements that, on Windows, equate to only allowing access to administrators and System.To make this easier,
- The OpenSSHUtils PowerShell module has been created to set the key ACLs properly, and should be installed on the server
- On first use of sshd, the key pair for the host will be automatically generated. If ssh-agent is running, the keys will be automatically added to the local store.
To make key authentication easy with an SSH server, run the following commands from an elevated PowerShell prompt:
Since there is no user associated with the sshd service, the host keys are stored under ProgramDatassh.
User key generation
To use key-based authentication, you first need to generate some public/private key pairs for your client.From PowerShell or cmd, use ssh-keygen to generate some key files.
This should display something like the following (where 'username' is replaced by your user name)
You can hit Enter to accept the default, or specify a path where you'd like your keys to be generated.At this point, you'll be prompted to use a passphrase to encrypt your private key files.The passphrase works with the key file to provide 2-factor authentication.For this example, we are leaving the passphrase empty.
Now you have a public/private ED25519 key pair(the .pub files are public keys and the rest are private keys):
Remember that private key files are the equivalent of a password should be protected the same way you protect your password.To help with that, use ssh-agent to securely store the private keys within a Windows security context, associated with your Windows login.To do that, start the ssh-agent service as Administrator and use ssh-add to store the private key.
After completing these steps, whenever a private key is needed for authentication from this client, ssh-agent will automatically retrieve the local private key and pass it to your SSH client.
Note
It is strongly recommended that you back up your private key to a secure location,then delete it from the local system, after adding it to ssh-agent.The private key cannot be retrieved from the agent.If you lose access to the private key, you would have to create a new key pairand update the public key on all systems you interact with.
Deploying the public key
To use the user key that was created above, the public key needs to be placed on the server into a text file called authorized_keys under usersusername.ssh.The OpenSSH tools include scp, which is a secure file-transfer utility, to help with this.
To move the contents of your public key (~.sshid_ed25519.pub) into a text file called authorized_keys in ~.ssh on your server/host.
This example uses the Repair-AuthorizedKeyPermissions function in the OpenSSHUtils module which was previously installed on the host in the instructions above.
These steps complete the configuration required to use key-based authentication with SSH on Windows.After this, the user can connect to the sshd host from any client that has the private key.