Creating Private Key and Public Key

What Is ssh-keygen?

Ssh-keygen is a tool for creating new authentication key pairs for SSH. Such key pairs are used for automating logins, single sign-on, and for authenticating hosts.

SSH Keys and Public Key Authentication

The SSH protocol uses public key cryptography for authenticating hosts and users. The authentication keys, called SSH keys, are created using the keygen program.

SSH introduced public key authentication as a more secure alternative to the older .rhosts authentication. It improved security by avoiding the need to have password stored in files, and eliminated the possibility of a compromised server stealing the user's password.

However, SSH keys are authentication credentials just like passwords. Thus, they must be managed somewhat analogously to user names and passwords. They should have a proper termination process so that keys are removed when no longer needed.

Creating an SSH Key Pair for User Authentication 





PuTTYgen is normally installed as part of the normal PuTTY .msi package installation. There is no need for a separate PuTTYgen download. Download the PuTTY installation package. For detailed installation instructions, see PuTTY installation instructions.

Runing PuTTYgen

PuTTYgen started

Creating a new key pair for authentication

To create a new key pair, select the type of key to generate from the bottom of the screen (using SSH-2 RSA with 2048 bit key size is good for most people; another good well-known alternative is ECDSA).

Then click Generate, and start moving the mouse within the Window. Putty uses mouse movements to collect randomness. The exact way you are going to move your mouse cannot be predicted by an external attacker. You may need to move the mouse for some time, depending on the size of your key. As you move it, the green progress bar should advance.

Once the progress bar becomes full, the actual key generation computation takes place. This may take from several seconds to several minutes. When complete, the public key should appear in the Window. You can now specify a passphrase for the key.

You should save at least the private key by clicking Save private key. It may be advisable to also save the public key, though it can be later regenerated by loading the private key (by clicking Load).

PuTTYgen generating RSA SSH key

We strongly recommended using a passphrase be for private key files intended for interactive use. If keys are needed for automation (e.g., with WinSCP, then they may be left without a passphrase.

puttygen created key and asking for passphase to save private key

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