Skip to content

Generating RSA Keys✯

An SSH key consists of

  • a public key that is intended to be distributed. This is the one to be placed on the target server
  • a private key that is confidential. This is the one that will be used by the SSH client
  • learn more about asymmetric encryption

Linux & Mac✯

  • Open a terminal - Enter the following command to generate an SSH key with a length of 4096 bytes:
ssh-keygen -b 4096

"Size matters", use a size of at least 4096.

  • You will get the following result; the command will ask you to modify the location of the private key:
Generating public/private rsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa):

While it is recommended to define a passphrase to protect the private key, keep in mind that this information will be requested each time the private key is used. This is also what we aim to avoid by using public/private keys...

Your identification has been saved in /home/user/.ssh/id_rsa.
Your public key has been saved in /home/user/.ssh/id_rsa.pub.
The key fingerprint is:
0a:3a:a4:ac:d1:40:6d:63:6d:fd:d9:fa:d6:b2:e0:36 user@host
The keys randomart image is:
+---[RSA 4096]----+
|      .          |
|                 |
| .               |
|. . . .          |
|. .=.o .S.       |
| =o.o. ..   .    |
|o +   .  . o ..  |
|.. .      oEoo . |
|o.        .o+oo  |
+-----------------+

  • The public key is stored in ~/.ssh/id_rsa.pub. This is the file to send when asked for your public key.

  • The private key is stored in ~/.ssh/id_rsa.

WARNING: The private part of the key must be kept securely, and access must be limited to authorized personnel only

On Windows✯

With PuTTY

PuTTY is the most widely used SSH client for Windows.

  • Download the PuTTYgen software to generate the key
  • Run the key generation software
  • In the field Number of bits in a generated key, specify the value 4096

PuTTY Key Generator

  • Click Generate (move the mouse in the gray area during the operation)
  • You can specify a passphrase if you wish
  • Save the private key by clicking on Save private key, give a name to this file (e.g., key.rsa)
  • Copy the public key displayed in the frame

Copying the public key