OpenSSH encryption - How to create and configure a public key in Linux

Setting up a public key

First of all, regardless if our Linux is a Debian, Red Hat, SuSe, etc, we must ensure that OpenSSH is the SSH application installed on the client system. The key generation varies under different implementation of SSH. Ssh-V command should display a line containing OpenSSH, followed by other details

 mail: ~ # ssh-V OpenSSH_4.3p2 Debian-9, OpenSSL 0.9.8c 05 Sep 2006 

Key generation

The RSA key pair must be generated on the client system. The public part of this key will be stored on servers to which we connect, while the private part of the key must be stored in a secure area of ​​the client system, by default in ~ / .ssh / id_rsa.

The key pair generation can be done with the ssh-keygen (1).

  fher98 @ deathbian: ~ $ mkdir ~ /. ssh
 fher98 @ deathbian: ~ $ chmod 700 ~ /. ssh
 fher98 @ deathbian: ~ $ ssh-keygen-q-f ~ / .ssh / id_rsa-t rsa
 Enter passphrase (empty for no passphrase):
 Enter passphrase Same again:

Do not use as your user password passphrase or leave it blank. The password should be at least 16 characters long, and not a simple prayer. A good option is a paragraph of a song or poem, using all possible grammatical symbols. During the configuration of ssh-agent will reduce the revenue required a password, so I recommend using a long passphrase.

File permissions should ensure that other users can not read data from the key pair. You may not permit the use OpenSSH public-key authentication if the file permissions are not sure. These changes must be made in all the systems involved.

  fher98 @ deathbian: ~ $ chmod go-w ~ /
 fher98 @ deathbian: ~ $ chmod 700 ~ /. ssh
 fher98 @ deathbian: ~ $ chmod go-rwx ~ /. ssh / *

Key distribution

The public part of RSA key pair must be copied to all servers that will be accessed by the client. The public key information to be copied can be found in the file ~ / .ssh / id_rsa.pub client. Assuming that all servers use OpenSSH instead of another different implementation of SSH public key must be added to the file ~ / .ssh / authorized_keys in each server.

Copy the public key from client to server

  fher98 @ deathbian: ~ $ scp ~ / .ssh / id_rsa.pub servidor.guatewireless.org:

 id_rsa.pub 100% 395 0.4KB / s 00:00

Now the public key is configured on the server

  server $ mkdir ~ /. ssh
 server $ chmod 700 ~ /. ssh
 server $ cat ~ / id_rsa.pub>> ~ / .ssh / authorized_keys
 server $ chmod 600 ~ / .ssh / authorized_keys
 server $ rm ~ / id_rsa.pub

Remember that you need to add new data from public keys in the authorized_keys file, so you can use multiple public keys on the same server. Each record in public key must be in a different line of the file.

To verify that connections to the server public keys are working properly engage in the following test;
From the client

  fher98 @ deathbian: ~ $ ssh-o = publickey servidor.guatewireless.org PreferredAuthentications
 Enter passphrase for key '/ ï ¿½ / .ssh / id_rsa': ï ¿½
 ï ¿½
 $ server

In a future article I'll show you how to configure ssh-agent process.

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