putty-source/doc/pubkey.but

\versionid $Id: pubkey.but,v 1.2 2001/02/06 09:34:42 owen Exp $

\# FIXME: passphrases, examples (e.g what does a key for pasting into
\# authorized_keys look like?), index entries, links.

\C{pubkey} Using public keys for SSH authentication

\H{pubkey-intro} Public key authentication - an introduction

\# Explain the basic principles of public key authentication. Many
\# people don't have the faintest idea what it is or why it's good.

\# Explain the dangers of leaving an unprotected private key around.
\# Explain passphrases, and urge that people NEVER store
\# unpassphrased keys unless they really need to or they can be sure
\# the machine is secure.

\H{pubkey-puttygen} PuTTYgen: RSA key generator for PuTTY

PuTTYgen is a key generator. It generates pairs of public and private
keys to be used with PuTTY, PSCP, and Plink, as well as the PuTTY
authentication agent, Pageant (see \k{pageant}).  PuTTYgen generates
RSA keys.

When you run PuTTYgen you will see a window where you have two
choices: \e{Generate} new public/private key pair or \e{Load} an
existing private key.

\S{pubkey-puttygen-generate} Generate a new key

Before generating a new key you have to chose the strength of the
encryption. With \e{Parameters} you define the strength of the key. The
default of 1024 should be OK for most users.

Pressing the \e{Generate} button starts the process of generating a
new key pair. You then have to move the mouse over the blank area in
order to generate random data for the algorithm. Continue until the
progress bar is complete.

As soon as enough random data is available the key is generated.  This 
may take a little while, especially on slow machines.  Once the key is 
generated, its details appear in the \e{Key} part of the PuTTYgen
window.

Now you can change the \e{Key comment} to something more meaningful
than the default (which is based on the current date).  e.g. add the
name of the host you will use it for. When using multiple keys a
meaningful comment may help you remember which passphrase to use!  You
should always enter a \e{Key passphrase} and \e{Confirm passphrase} to
protect your keys.

\# Mention a good length for a passphrase. (I think Schneier
\# said something about this on counterpane.com once.)

\# In case people don't like the idea of exchanging a short password
\# typed every time for a longer passphrase typed every time, link
\# to the Pageant chapter.

Finally save the key by pressing the \e{Save} button. Do not close the
window but proceed with step \k{pubkey-gettingready}, otherwise you
will have to \e{Load} the private key again as described below.

\S{pubkey-puttygen-load} Load and modify a key

PuTTYgen does not store the public key in a file by default. If you
have to distribute the public key you can press the \e{Load} button,
select the private key file, and PuTTYgen will give you the public key
again.  You can also change the comment and passphrase for your
private key this way. Just modify the values and \e{Save} the key.

\S{pubkey-gettingready} Getting ready for public key authentication

Connect to your SSH server using PuTTY with the SSH protocol. When the
connection succeeds you will be prompted for your user name and
password to login. Once logged in change into the \c{.ssh} directory
and open the file \c{authorized_keys} with your favorite editor (you
may have to create this file if this is the first key to add).

Switch to the PuTTYgen window and select all of the content below
\e{Public key for pasting into authorized_keys file}, copy it to the
clipboard (\c{Ctrl+C}). Then, switch back to the PuTTY window and
insert the data into the open file. Save the file.

From now on you can use the private key for authentication to this
host.  Either select the private key in PuTTY's \e{Connection},
\e{SSH} panel: \e{Private key file for authentication} dialog or use
it with Pageant as described in \k{pageant}.