PuTTY's authentication agent Pageant (see http://the.earth.li/~sgtatham/putty/latest/htmldoc/Chapter9.html) keeps the decrypted private keys in the memory and, if required, generates signatures and handles the authentication procedure.
You list the keys stored by Pageant as follows:
> | Start the Pageant program. |
> | Right-click the Pageant icon in the taskbar. A menu opens. |
> | Select View Keys. Pageant’s main window opens, which incorporates a list box containing all the private keys currently stored by Pageant. |
If the required key is not yet included, enter it as follows:
> | Click Add Key. Pageant then opens the dialog box Select Private Key File. |
> | From this dialog box select the file which belongs to your private key and click Open. Pageant then loads the private key into the memory. If the key is protected by a passphrase, Pageant requests this passphrase. As soon as the key is loaded, it appears in the list box of the main Pageant window. |
You can now start PuTTY and open an SSH connection to a system which accepts your key. PuTTY recognizes that Pageant is running, fetches the key automatically from Pageant, and uses it for authentication purposes. You can now open further PuTTY connections without having to type in the passphrase each time.