Generate A Private Key On Linux
Several tools exist to generate SSH public/private key pairs. The following sections show how to generate an SSH key pair on UNIX, UNIX-like and Windows platforms.
Generate Public Key Linux
Generating an SSH Key Pair on UNIX and UNIX-Like Platforms Using the ssh-keygen Utility
UNIX and UNIX-like platforms (including Solaris and Linux) include the ssh-keygen utility to generate SSH key pairs.
The -y option will read a private SSH key file and prints an SSH public key to stdout. The public key part is redirected to the file with the same name as the private key but with the.pub file extension. If the key has a password set, the password will be required to generate the public key. I have a file server.key generated by openssl genrsa -out server.key 2048, which contains both public and private key. I searched and fount that I can get public key by openssl rsa -in server.key.
- Navigate to your home directory:
- Run the ssh-keygen utility, providing as
filename
your choice of file name for the private key:The ssh-keygen utility prompts you for a passphrase for the private key.
- Enter a passphrase for the private key, or press Enter to create a private key without a passphrase:
Note:
While a passphrase is not required, you should specify one as a security measure to protect the private key from unauthorized use. When you specify a passphrase, a user must enter the passphrase every time the private key is used.
The ssh-keygen utility prompts you to enter the passphrase again.
- Enter the passphrase again, or press Enter again to continue creating a private key without a passphrase:
- The ssh-keygen utility displays a message indicating that the private key has been saved as
filename
and the public key has been saved asfilename
.pub
. It also displays information about the key fingerprint and randomart image.
Generating an SSH Key Pair on Windows Using the PuTTYgen Program
The PuTTYgen program is part of PuTTY, an open source networking client for the Windows platform.
- Download and install PuTTY or PuTTYgen.
To download PuTTY or PuTTYgen, go to http://www.putty.org/ and click the You can download PuTTY here link.
- Run the PuTTYgen program.
- Set the Type of key to generate option to SSH-2 RSA.
- In the Number of bits in a generated key box, enter 2048.
- Click Generate to generate a public/private key pair.
As the key is being generated, move the mouse around the blank area as directed.
- (Optional) Enter a passphrase for the private key in the Key passphrase box and reenter it in the Confirm passphrase box.
Note: /windows-10-product-key-generator-tool.html.
While a passphrase is not required, you should specify one as a security measure to protect the private key from unauthorized use. When you specify a passphrase, a user must enter the passphrase every time the private key is used.
- Click Save private key to save the private key to a file. To adhere to file-naming conventions, you should give the private key file an extension of
.ppk
(PuTTY private key).Note:
The.ppk
file extension indicates that the private key is in PuTTY's proprietary format. You must use a key of this format when using PuTTY as your SSH client. It cannot be used with other SSH client tools. Refer to the PuTTY documentation to convert a private key in this format to a different format. - Select all of the characters in the Public key for pasting into OpenSSH authorized_keys file box.
Make sure you select all the characters, not just the ones you can see in the narrow window. If a scroll bar is next to the characters, you aren't seeing all the characters.
- Right-click somewhere in the selected text and select Copy from the menu.
- Open a text editor and paste the characters, just as you copied them. Start at the first character in the text editor, and do not insert any line breaks.
- Save the text file in the same folder where you saved the private key, using the
.pub
extension to indicate that the file contains a public key. - If you or others are going to use an SSH client that requires the OpenSSH format for private keys (such as the
ssh
utility on Linux), export the private key:- On the Conversions menu, choose Export OpenSSH key.
- Save the private key in OpenSSH format in the same folder where you saved the private key in
.ppk
format, using an extension such as.openssh
to indicate the file's content.
If you want to convert your website from HTTP to HTTPS, you need to get a SSL certificate from a valid organization like Verisign or Thawte. You can also generate self signed SSL certificate for testing purpose.
In this article, let us review how to generate private key file (server.key), certificate signing request file (server.csr) and webserver certificate file (server.crt) that can be used on Apache server with mod_ssl.
Key, CSR and CRT File Naming Convention
I typically like to name the files with the domain name of the HTTPS URL that will be using this certificate. /company-of-heroes-cd-key-generator.html. This makes it easier to identify and maintain.
- Instead of server.key, I use www.thegeekstuff.com.key
- Instead of server.csr, I use www.thegeekstuff.com.csr
- Instead of server.crt, I use www.thegeekstuff.com.crt
1. Generate Private Key on the Server Running Apache + mod_ssl
First, generate a private key on the Linux server that runs Apache webserver using openssl command as shown below.

The generated private key looks like the following.
2. Generate a Certificate Signing Request (CSR)
Using the key generate above, you should generate a certificate request file (csr) using openssl as shown below.
3. Generate a Self-Signed SSL Certificate
For testing purpose, you can generate a self-signed SSL certificate that is valid for 1 year using openssl command as shown below.
You can use this method to generate Apache SSL Key, CSR and CRT file in most of the Linux, Unix systems including Ubuntu, Debian, CentOS, Fedora and Red Hat.
4. Get a Valid Trial SSL Certificate (Optional)
Instead of signing it youself, you can also generate a valid trial SSL certificate from thawte. i.e Before spending the money on purchasing a certificate, you can also get a valid fully functional 21 day trial SSL certificates from Thawte. Once this valid certificate works, you can either decide to purchase it from Thawte or any other SSL signing organization.
This step is optional and not really required. For testing purpose, you can always use the self-signed certificate that was generated from the above step.
Go to Thwate trial certificate request page and do the following:
- Select “SSL Web Server Certificate (All servers)” under the “select your trial certificate”.
- Do not check the PKCS #7 check-box under the “configure certificate”
- Copy/Paste the *.csr file that you generate above in the textbox under “certificate signing request (CSR)”
- Click on next at the bottom, which will give you a 21-day free trial certificate.
Copy/Paste the trial certificate to the www.thegeekstuff.com.crt file as shown below.
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