Linux ssh-keygen and openssl commands

• ssh-keygen
  This command will create a pair of private and public keys.
  It will ask for the location of the key and whether to use a passphrase.

  
  [oren@localhost ~]$ ssh-keygen 
  Generating public/private rsa key pair.
  Enter file in which to save the key (/home/oren/.ssh/id_rsa): 
  /home/oren/.ssh/id_rsa already exists.
  Overwrite (y/n)? y
  Enter passphrase (empty for no passphrase): 
  Enter same passphrase again: 
  Your identification has been saved in /home/oren/.ssh/id_rsa.
  Your public key has been saved in /home/oren/.ssh/id_rsa.pub.
  The key fingerprint is:
  89:17:86:82:6c:7f:8b:b2:2c:0f:d3:52:30:e0:20:86 oren@localhost.localdomain
  The key's randomart image is:
  +--[ RSA 2048]----+
  |=.               |
  |E. .   .         |
  |o.+ . . o        |
  | + . . o o       |
  |  . . o S        |
  | o   o o         |
  |+ o . .          |
  |.= o             |
  | o+              |
  +-----------------+

  By default, it creates a key with a strength of 2048 bits.
  The two key files are:
  ~/.ssh/id_rsa  this is the private key
  ~/.ssh/id_rsa.pub this is the public key, you upload this key to the server you want to connect with ssh.

• if we want key stronger than 2048 bits, we can use the -b option.
  4096 bits is usually supported by most of the server, we create a key with this strength by running the following:

  ssh-keygen -b 4096

• ssh-keygen -p
  we can use the -p option to remove or change the passphrase of the key file, as long as we know the passphrase.
• ssh-keygen -l
  will display the ssh key fingerprint which is a unique cryptographic identifier.
• openssl dhparam <bitSize> -text 
  find a prime number with the size of bitSize.