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.
Generate SSH Keys on Linux. SSH is a cryptographic network protocol which is used to securely connect to a host over an unsecured connection. By default, any Linux operating system supports SSH; hence using a third party client is unnecessary like in the Windows platform. Dec 07, 2019 SSH works using a key pair; the public key and the private key. The private key is kept on the computer you log in from, while the public key is stored in the.ssh/authorizedkeys file on all the computers you want to log into. The public key.
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.
I'm trying to create an ssh key for another user. I'm logged in as root. If you generate the key for the user you also have to have a secure method of getting the private key and it's pass phrase to the user. Browse other questions tagged linux centos ssh ssh-keys or ask your own question. Ssh-keygen -f anything creates two files in the current directory. Anything.pub is the public key, which you could append to the user's /.ssh/authorizedkeys on any destination server. The other file, just called anything is the private key and therefore should be stored safely for the user.
~/.ssh/identity.pub
contains the protocol version 1 RSA public key~/.ssh/id_dsa c
ontains the protocol version 2 DSA authentication identity of the user.~/.ssh/id_dsa.pub c
ontains the protocol version 2 DSA public key for authentication~/.ssh/id_rsa c
ontains the protocol version 2 RSA authentication identity of the user~/.ssh/id_rsa.pub c
ontains the protocol version 2 RSA public key for authenticationGenerating 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.
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 -f
option 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.
With a secure shell (SSH) key pair, you can create virtual machines (VMs) in Azure that use SSH keys for authentication, eliminating the need for passwords to sign in. This article shows you how to quickly generate and use an SSH public-private key file pair for Linux VMs. You can complete these steps with the Azure Cloud Shell, a macOS or Linux host, the Windows Subsystem for Linux, and other tools that support OpenSSH.
Note
VMs created using SSH keys are by default configured with passwords disabled, which greatly increases the difficulty of brute-force guessing attacks.
For more background and examples, see Detailed steps to create SSH key pairs.
For additional ways to generate and use SSH keys on a Windows computer, see How to use SSH keys with Windows on Azure.
Azure currently supports SSH protocol 2 (SSH-2) RSA public-private key pairs with a minimum length of 2048 bits. Other key formats such as ED25519 and ECDSA are not supported.
Use the ssh-keygen
command to generate SSH public and private key files. By default, these files are created in the ~/.ssh directory. You can specify a different location, and an optional password (passphrase) to access the private key file. If an SSH key pair with the same name exists in the given location, those files are overwritten.
The following command creates an SSH key pair using RSA encryption and a bit length of 4096:
If you use the Azure CLI to create your VM with the az vm create command, you can optionally generate SSH public and private key files using the --generate-ssh-keys
option. The key files are stored in the ~/.ssh directory unless specified otherwise with the --ssh-dest-key-path
option. The --generate-ssh-keys
option will not overwrite existing key files, instead returning an error. In the following command, replace VMname and RGname with your own values:
To create a Linux VM that uses SSH keys for authentication, specify your SSH public key when creating the VM using the Azure portal, Azure CLI, Azure Resource Manager templates, or other methods:
If you're not familiar with the format of an SSH public key, you can display your public key with the following cat
command, replacing ~/.ssh/id_rsa.pub
with the path and filename of your own public key file if needed:
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A typical public key value looks like this example:
If you copy and paste the contents of the public key file to use in the Azure portal or a Resource Manager template, make sure you don't copy any trailing whitespace. To copy a public key in macOS, you can pipe the public key file to pbcopy
. Similarly in Linux, you can pipe the public key file to programs such as xclip
.
The public key that you place on your Linux VM in Azure is by default stored in ~/.ssh/id_rsa.pub, unless you specified a different location when you created the key pair. To use the Azure CLI 2.0 to create your VM with an existing public key, specify the value and optionally the location of this public key using the az vm create command with the --ssh-key-values
option. In the following command, replace VMname, RGname, and keyFile with your own values:
If you want to use multiple SSH keys with your VM, you can enter them in a space-separated list, like this --ssh-key-values sshkey-desktop.pub sshkey-laptop.pub
.
With the public key deployed on your Azure VM, and the private key on your local system, SSH into your VM using the IP address or DNS name of your VM. In the following command, replace azureuser and myvm.westus.cloudapp.azure.com with the administrator user name and the fully qualified domain name (or IP address):
If you specified a passphrase when you created your key pair, enter that passphrase when prompted during the login process. The VM is added to your ~/.ssh/known_hosts file, and you won't be asked to connect again until either the public key on your Azure VM changes or the server name is removed from ~/.ssh/known_hosts. Generating on an ssh2 public key osx windows 7.
If the VM is using the just-in-time access policy, you need to request access before you can connect to the VM. For more information about the just-in-time policy, see Manage virtual machine access using the just in time policy.
For more information on working with SSH key pairs, see Detailed steps to create and manage SSH key pairs.
If you have difficulties with SSH connections to Azure VMs, see Troubleshoot SSH connections to an Azure Linux VM.