While Encrypting a File with a Password from the Command Line using OpenSSLis very useful in its own right, the real power of the OpenSSL library is itsability to support the use of public key cryptograph for encrypting orvalidating data in an unattended manner (where the password is not required toencrypt) is done with public keys.
The Commands to Run
Generate a 2048 bit RSA Key
Generate 2048 Bit Key Generate 1024 Bit Key. The less secure key size is 1024 bit. We do not recommend usage of this size of keys but in some situations like old systems we may need this size of keys. Here how we can generate 1024 bit key with ssh-keygen. $ ssh-keygen -b 1024. Unable to use key file 'C: publickey idrsa.ppk' (OpenSSH SSH-2 private key (old PEM format)) login as: Below is the command which i used to generate key pairs on windows 10. C: Users xxxssh-keygen -t rsa -b 2048 -C 'azureuser@vm' Generating public/private rsa key pair. To generate an RSA key pair for version 1 of the SSH protocol, follow these steps: Generate an RSA key pair by typing the following at a shell prompt: $ ssh-keygen -t rsa1 Generating public/private rsa1 key.
You can generate a public and private RSA key pair like this:
openssl genrsa -des3 -out private.pem 2048
That generates a 2048-bit RSA key pair, encrypts them with a password you provideand writes them to a file. You need to next extract the public key file. You willuse this, for instance, on your web server to encrypt content so that it canonly be read with the private key.
Export the RSA Public Key to a File
This is a command that is
openssl rsa -in private.pem -outform PEM -pubout -out public.pem
The
-pubout
flag is really important. Be sure to include it.Next open the
public.pem
and ensure that it starts with-----BEGIN PUBLIC KEY-----
. This is how you know that this file is thepublic key of the pair and not a private key.To check the file from the command line you can use the
less
command, like this:less public.pem
Do Not Run This, it Exports the Private Key
A previous version of the post gave this example in error.
openssl rsa -in private.pem -out private_unencrypted.pem -outform PEM
The error is that the
-pubout
was dropped from the end of the command.That changes the meaning of the command from that of exporting the public keyto exporting the private key outside of its encrypted wrapper. Inspecting theoutput file, in this case private_unencrypted.pem
clearly shows that the keyis a RSA private key as it starts with -----BEGIN RSA PRIVATE KEY-----
.Visually Inspect Your Key Files
It is important to visually inspect you private and public key files to makesure that they are what you expect. OpenSSL will clearly explain the nature ofthe key block with a
-----BEGIN RSA PRIVATE KEY-----
or -----BEGIN PUBLIC KEY-----
.You can use less to inspect each of your two files in turn:
less private.pem
to verify that it starts with a-----BEGIN RSA PRIVATE KEY-----
less public.pem
to verify that it starts with a-----BEGIN PUBLIC KEY-----
The next section shows a full example of what each key file should look like.
The Generated Key Files
The generated files are base64-encoded encryption keys in plain text format.If you select a password for your private key, its file will be encrypted withyour password. Be sure to remember this password or the key pair becomes useless.
The private.pem file looks something like this:
The public key, public.pem, file looks like:
Protecting Your Keys
Depending on the nature of the information you will protect, it’s important tokeep the private key backed up and secret. The public key can be distributedanywhere or embedded in your web application scripts, such as in your PHP,Ruby, or other scripts. Again, backup your keys!
Remember, if the key goes away the data encrypted to it is gone. Keeping aprinted copy of the key material in a sealed envelope in a bank safety depositbox is a good way to protect important keys against loss due to fire or harddrive failure.
Oh, and one last thing.
If you, dear reader, were planning any funny business with the private key that I have just published here. Know that they were made especially for this series of blog posts. I do not use them for anything else.
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How To Generate Ssh Key Pair
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How to Generate Keys and What Are They?
Generating SSH key pair consists of two basic phases. The first phase is generating the key pair on the local side, the second phase is copying it to the remote host, registering in the server and configuring the ssh daemon to make it useful. A key pair consists of two files, id_rsa and id_rsa.pub which are private and public keys respectively. The public key resides on the server side, whereas the private key is used when accessing it over SSH protocol.
In the following example ssh-keygen command is used to generate the key pair. When generating the key pair, the command prompt asks a name for a key, if it’s omitted the default name – id_rsa is used instead.
How to Use the Keys?
Once the key pair is generated on the local side through terminal window, the next step is to prepare them for employing for authentication purpose. The most convenient way to upload and register the public key in the server is using the ssh-copy-id command, what it does is copy the public key to the given user account located in the given host. As seen in the following example when the ssh-copy-id, username, the host name along with the password are all given the public key is copied and registered on the server side. If the username is root, the public key is uploaded to /root/.ssh/ on the server.
That being said, the server still isn’t protected with the SSH key pair as it’s not configured properly. Anyone can still access to the server if the password of the user account is known; hence the password has to be disabled while enabling the key pair verification. To disable the password authentication, edit /etc/ssh/sshd_config file where the settings for the SSH daemon are contained. In the file, the PasswordAuthentication has to be altered to NO, ChallengeResponseAuthentication should be altered to No as well. As the next step the sshd daemon has to be restarted for changes to take effect, which can be done with sudo systemctl reload sshd. Finally, the new key pair authentication method can be tested by giving ssh username@username in the terminal window.
Theory of The Keys and How They Work
The key pair is a part of the SSH standard which is used to connect to a remote host over an unsecured network. As stated earlier, the key pair consists of two keys – public and private keys which are uploaded to the server side and kept on the client side respectively. The public key is denoted by .pub extension, and the private key doesn’t have any extension.
When the user is accessing the server, the SSH daemon installed on the server side requests the user for the SSH private key, if it’s provided the private key is compared against the public key in the server. If the private key corresponds to the public key, authentication is successful, otherwise it rejects the login request. By default, the key pair uses RSA which is a cryptographic algorithm to generate the keys. But there are other popular algorithms as well, such as DSA and ECDSA.
ssh-keygen Command Line Options
ssh-keygen is used to generate keys and it provides a number of options to ease the key pair management, tighten the security and increase the flexibility. The following options are some of the prominent options which may come handy when managing a server.
Passphrase
The Passphrase option is used to provide a secondary protection when a key pair is used to authenticate the user. What it does is to secure the private key with a password and consequently the user is required to provide the passphrase when logging in to the remote host. It asks during the key pair creation.
Change the Bit Strength
Bit strength refers to the key pair’s key size which defines how strong the key pair is. Nowadays the standard size is 2048 bits, but it used to be 1024 bits and is no longer acceptable as it’s speculated that many powerful hardware are capable of cracking anything up to 1024 bits or even above given the right amount of time. Fortunately, ssh-keygen currently supports higher bit strength values such as 2048 and its next fashionable number 4096 which is recommended if it’s possible due to the large bit strength. The bit strength value can be adjusted with –b command, if it’s omitted the default value – 1024 or 2048 depending on the ssh-keygen is used.
Comment Public Key
Linux Generate Ssh Key 2048 Download
Commenting is applicable to the public key, and is useful in organizing the keys if there are a large number of keys involved. The typical usage of commenting is when multiple admins use a server, but still want to distinguish one key from another. The following format is used to add a comment when generating a key pair.
Linux Generate Ssh Key 2048 Free
Change Passphrase of a Private Key
Like adding a passphrase when generating a key pair, the existing passphrase can also be changed. Since the passphrase is applicable to the private key which resides on the client side, the command has to be executed on the client side along with the name of the private key. This option takes 3 parameters, old password, new password and the private key to apply the changes.
Linux Generate Public Key
Change the Cryptographic Algorithm
Linux Generate Ssh Key 2048 Windows 10
The Algorithm defines how the information in the key pair is encrypted in order to verify each other when the connection is being established. Ssh-keygen supports several popular algorithm types which are RSA, ECDSA, DSA, ED25519 and RSA1. Nowadays the popular algorithm among many servers is RSA due to its wide spread usage and relatively good security, however it’s currently being upgraded to the newer version ECDSA which is much lighter, and has a low bit value with a high security compared to RSA. ED25519 is the newest version among these, and therefore not many clients support it, but still server side implementation is possible at the moment. DSA is the oldest version among all these algorithms, and is no longer employed in most of the hosts as it’s not secure anymore. According to OpenSSH 7 standard the support for DSA will no longer be given. The format to use the algorithm is as following.