-\versionid $Id: pubkey.but,v 1.11 2001/12/06 20:05:39 simon Exp $
-
-\# FIXME: passphrases, examples (e.g what does a key for pasting into
-\# authorized_keys look like?), index entries, links.
+\versionid $Id: pubkey.but,v 1.12 2001/12/12 18:45:56 simon Exp $
\C{pubkey} Using public keys for SSH authentication
disk. Many people feel this is a good compromise between security
and convenience. See \k{pageant} for further details.
-\S{pubkey-types} Different types of public key
+There is more than one public-key algorithm available. The most
+common is RSA, but others exist, notably DSA (otherwise known as
+DSS), the USA's federal Digital Signature Standard. The key types
+supported by PuTTY are described in \k{puttygen-keytype}.
+
+\H{pubkey-puttygen} Using PuTTYgen, the PuTTY key generator
+
+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: \q{Generate}, to generate a new public/private key pair, or
+\q{Load} to load in an existing private key.
+
+\S{puttygen-generating} Generating a new key
+
+This is a general outline of the procedure for generating a new key
+pair. The following sections describe the process in more detail.
+
+\b First, you need to select which type of key you want to generate,
+and also select the strength of the key. This is described in more
+detail in \k{puttygen-keytype} and
+\k{puttygen-strength}.
+
+\b Then press the \q{Generate} button, to actually generate the key.
+\K{puttygen-generate} describes this step.
+
+\b Once you have generated the key, select a comment field
+(\k{puttygen-comment}) and a passphrase (\k{puttygen-passphrase}).
+
+\b Now you're ready to save the private key to disk; press the
+\q{Save private key} button. (See \k{puttygen-savepriv}).
+
+Your key pair is now ready for use. You may also want to copy the
+public key to your server, either by copying it out of the \q{Public
+key for pasting into authorized_keys file} box (see
+\k{puttygen-pastekey}), or by using the \q{Save public key} button
+(\k{puttygen-savepub}). However, you don't need to do this
+immediately; if you want, you can load the private key back into
+PuTTYgen later (see \k{puttygen-load}) and the public key will be
+available for copying and pasting again.
-The PuTTY key generator, described in \k{pubkey-puttygen}, offers
-you the opportunity to generate several types of key pair:
+\k{pubkey-gettingready} describes the typical process of configuring
+PuTTY to attempt public-key authentication, and configuring your SSH
+server to accept it.
+
+\S{puttygen-keytype} Selecting the type of key
+
+\cfg{winhelp-topic}{puttygen.keytype}
+
+Before generating a public key using PuTTYgen, you need to select
+which type of key you need. PuTTYgen currently supports three types
+of key:
\b An RSA key for use with the SSH 1 protocol.
using the SSH 1 protocol, you must select the first key type or your
key will be completely useless.
-SSH 2 supports more than one key type. The two types supported by
-PuTTY are RSA and DSA.
+The SSH 2 protocol supports more than one key type. The two types
+supported by PuTTY are RSA and DSA.
The PuTTY developers \e{strongly} recommend you use RSA. DSA has an
intrinsic weakness which makes it very easy to create a signature
DSA, we recommend you do not use the same key to authenticate with
more than one server.
-\H{pubkey-puttygen} PuTTYgen: Key generator for PuTTY
+\S{puttygen-strength} Selecting the size (strength) of the key
-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.
+\cfg{winhelp-topic}{puttygen.bits}
-When you run PuTTYgen you will see a window where you have two
-choices: \q{Generate}, to generate a new public/private key pair, or
-\q{Load} to load in an existing private key.
+The \q{Number of bits} input box allows you to choose the strength
+of the key PuTTYgen will generate.
+
+Currently 1024 bits should be sufficient for most purposes.
+
+\S{puttygen-generate} The \q{Generate} button
+
+\cfg{winhelp-topic}{puttygen.generate}
+
+Once you have chosen the type of key you want, and the strength of
+the key, press the \q{Generate} button and PuTTYgen will begin the
+process of actually generating the key.
+
+First, a progress bar will appear and PuTTYgen will ask you to move
+the mouse around to generate randomness. Wave the mouse in circles
+over the blank area in the PuTTYgen window, and the progress bar
+will gradually fill up as PuTTYgen collects enough randomness. You
+don't need to wave the mouse in particularly imaginative patterns
+(although it can't hurt); PuTTYgen will collect enough randomness
+just from the fine detail of \e{exactly} how far the mouse has moved
+each time Windows samples its position.
+
+When the progress bar reaches the end, PuTTYgen will begin creating
+the key. The progress bar will reset to the start, and gradually
+move up again to track the progress of the key generation. It will
+not move evenly, and may occasionally slow down to a stop; this is
+unfortunately unavoidable, because key generation is a random
+process and it is impossible to reliably predict how long it will
+take.
+
+When the key generation is complete, a new set of controls will
+appear in the window to indicate this.
+
+\S{puttygen-fingerprint} The \q{Key fingerprint} box
-\S{pubkey-puttygen-generate} Generate a new key
-
-Before generating a new key you have to choose the strength of the
-encryption, and the type of the key (see \k{pubkey-types}). With
-\q{Parameters} you define the strength of the key. The default of
-1024 should be OK for most users.
-
-Pressing the \q{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 \q{Key} part of the PuTTYgen
-window.
-
-Now you can change the \q{Key comment} field 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 passphrase in the
-\q{Key passphrase} and \q{Confirm passphrase} fields, to protect
-your keys.
-
-(Choosing a good passphrase is difficult. Just as you shouldn't use
-a dictionary word as a password because it's easy for an attacker to
+\cfg{winhelp-topic}{puttygen.fingerprint}
+
+The \q{Key fingerprint} box shows you a fingerprint value for the
+generated key. This is derived cryptographically from the \e{public}
+key value, so it doesn't need to be kept secret.
+
+The fingerprint value is intended to be cryptographically secure, in
+the sense that it is computationally infeasible for someone to
+invent a second key with the same fingerprint, or to find a key with
+a particular fingerprint. So some utilities, such as the Pageant key
+list box (see \k{pageant-mainwin-keylist}) and the Unix \c{ssh-add}
+utility, will list key fingerprints rather than the whole public key.
+
+\S{puttygen-comment} Setting a comment for your key
+
+\cfg{winhelp-topic}{puttygen.comment}
+
+If you have more than one key and use them for different purposes,
+you don't need to memorise the key fingerprints in order to tell
+them apart. PuTTY allows you to enter a \e{comment} for your key,
+which will be displayed whenever PuTTY or Pageant asks you for the
+passphrase.
+
+The default comment format, if you don't specify one, contains the
+key type and the date of generation, such as \c{rsa-key-20011212}.
+Another commonly used approach is to use your name and the name of
+the computer the key will be used on, such as \c{simon@simons-pc}.
+
+To alter the key comment, just type your comment text into the
+\q{Key comment} box before saving the private key. If you want to
+change the comment later, you can load the private key back into
+PuTTYgen, change the comment, and save it again.
+
+\S{puttygen-passphrase} Setting a passphrase for your key
+
+\cfg{winhelp-topic}{puttygen.passphrase}
+
+The \q{Key passphrase} and \q{Confirm passphrase} boxes allow you to
+choose a passphrase for your key. The passphrase will be used to
+encrypt the key on disk, so you will not be able to use the key
+without first entering the passphrase.
+
+When you save the key, PuTTY will check that the \q{Key passphrase}
+and \q{Confirm passphrase} boxes both contain exactly the same
+passphrase, and will refuse to save the key otherwise.
+
+If you leave the passphrase fields blank, the key will be saved
+unencrypted. You should \e{not} do this without good reason; if you
+do, your private key file on disk will be all an attacker needs to
+gain access to any machine configured to accept that key. If you
+want to be able to log in without having to type a passphrase every
+time, you should consider using Pageant (\k{pageant}) so that your
+decrypted key is only held in memory rather than on disk.
+
+Under special circumstances you may genuinely \e{need} to use a key
+with no passphrase; for example, if you need to run an automated
+batch script that needs to make an SSH connection, you can't be
+there to type the passphrase. In this case we recommend you generate
+a special key for each specific batch script (or whatever) that
+needs one, and on the server side you should arrange that each key
+is \e{restricted} so that it can only be used for that specific
+purpose. The documentation for your SSH server should explain how to
+do this (it will probably vary between servers).
+
+Choosing a good passphrase is difficult. Just as you shouldn't use a
+dictionary word as a password because it's easy for an attacker to
run through a whole dictionary, you should not use a song lyric,
quotation or other well-known sentence as a passphrase. DiceWare
(\W{http://www.diceware.com/}\cw{www.diceware.com}) recommends using
which gives over 2^64 possible passphrases and is probably not a bad
scheme. If you want your passphrase to make grammatical sense, this
cuts down the possibilities a lot and you should use a longer one as
-a result.)
+a result.
+
+\e{Do not forget your passphrase}. There is no way to recover it.
+
+\S{puttygen-savepriv} Saving your private key to a disk file
+
+\cfg{winhelp-topic}{puttygen.savepriv}
+
+Once you have generated a key, set a comment field and set a
+passphrase, you are ready to save your private key to disk.
+
+Press the \q{Save private key} button. PuTTYgen will put up a dialog
+box asking you where to save the file. Select a directory, type in a
+file name, and press \q{Save}.
-Finally save the key by pressing the \q{Save} button. Do not close the
-window but proceed with step \k{pubkey-gettingready}, otherwise you
-will have to load the private key again (as described below).
+This file is the one you will need to tell PuTTY to use for
+authentication (see \k{config-ssh-privkey}) or tell Pageant to load
+(see \k{pageant-mainwin-addkey}).
-\S{pubkey-puttygen-load} Load and modify a key
+\S{puttygen-savepub} Saving your public key to a disk file
-PuTTYgen does not store the public key in a file by default. If you
-have to distribute the public key you can press the \q{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 save the key.
+\cfg{winhelp-topic}{puttygen.savepub}
-\S{pubkey-gettingready} Getting ready for public key authentication
+The SSH 2 protocol drafts specify a standard format for storing
+public keys on disk. Some SSH servers (such as \cw{ssh.com}'s)
+require a public key in this format in order to accept
+authentication with the corresponding private key. (Others, such as
+OpenSSH, use a different format; see \k{puttygen-pastekey}.)
+
+To save your public key in the SSH 2 standard format, press the
+\q{Save public key} button in PuTTYgen. PuTTYgen will put up a
+dialog box asking you where to save the file. Select a directory,
+type in a file name, and press \q{Save}.
+
+You will then probably want to copy the public key file to your SSH
+server machine. See \k{pubkey-gettingready} for general instructions
+on configuring public-key authentication once you have generated a
+key.
+
+If you use this option with an SSH 1 key, the file PuTTYgen saves
+will contain exactly the same text that appears in the \q{Public key
+for pasting} box. This is the only existing standard for SSH 1
+public keys.
+
+\S{puttygen-pastekey} \q{Public key for pasting into authorized_keys
+file}
+
+\cfg{winhelp-topic}{puttygen.pastekey}
+
+All SSH 1 servers require your public key to be given to it in a
+one-line format before it will accept authentication with your
+private key. The OpenSSH server also requires this for SSH 2.
+
+The \q{Public key for pasting into authorized_keys file} gives the
+public-key data in the correct one-line format. Typically you will
+want to select the entire contents of the box using the mouse, press
+Ctrl+C to copy it to the clipboard, and then paste the data into a
+PuTTY session which is already connected to the server.
+
+See \k{pubkey-gettingready} for general instructions on configuring
+public-key authentication once you have generated a key.
+
+\S{puttygen-load} Reloading a private key
+
+\cfg{winhelp-topic}{puttygen.load}
+
+PuTTYgen allows you to load an existing private key file into
+memory. If you do this, you can then change the passphrase and
+comment before saving it again; you can also make extra copies of
+the public key.
+
+To load an existing key, press the \q{Load} button. PuTTYgen will
+put up a dialog box where you can browse around the file system and
+find your key file. Once you select the file, PuTTYgen will ask you
+for a passphrase (if necessary) and will then display the key
+details in the same way as if it had just generated the key.
+
+\H{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
with your favorite editor. (You may have to create this file if this
is the first key you have put in it). Then switch to the PuTTYgen
window, select all of the text in the \q{Public key for pasting into
-authorized_keys file} box, and copy it to the clipboard
-(\c{Ctrl+C}). Then, switch back to the PuTTY window and insert the
-data into the open file, making sure it ends up all on one line.
-Save the file.
+authorized_keys file} box (see \k{puttygen-pastekey}), and copy it
+to the clipboard (\c{Ctrl+C}). Then, switch back to the PuTTY window
+and insert the data into the open file, making sure it ends up all
+on one line. Save the file.
\b If your server is OpenSSH and is using the SSH 2 protocol, you
-should follow the same instructions except that the file will be
-called \c{authorized_keys2}.
+should follow the same instructions, except that in earlier versions
+of OpenSSH 2 the file might be called \c{authorized_keys2}. (In
+modern versions the same \c{authorized_keys} file is used for both
+SSH 1 and SSH 2 keys.)
\b If your server is \cw{ssh.com}'s SSH 2 product, you need to save
-a \e{public} key file from PuTTYgen, and copy that into the
-\c{.ssh2} directory on the server. Then you should go into that
-\c{.ssh2} directory, and edit (or create) a file called
-\c{authorization}. In this file you should put a line like \c{Key
-mykey.pub}, with \c{mykey.pub} replaced by the name of your key
-file.
+a \e{public} key file from PuTTYgen (see \k{puttygen-savepub}), and
+copy that into the \c{.ssh2} directory on the server. Then you
+should go into that \c{.ssh2} directory, and edit (or create) a file
+called \c{authorization}. In this file you should put a line like
+\c{Key mykey.pub}, with \c{mykey.pub} replaced by the name of your
+key file.
\b For other SSH server software, you should refer to the manual for
that server.
-From now on you should be able to use the private key for
-authentication to this host. Either select the private key in
-PuTTY's \q{Connection}, \q{SSH} panel: \q{Private key file for
-authentication} dialog or use it with Pageant as described in
-\k{pageant}.
+You may also need to ensure that your home directory, your \c{.ssh}
+directory, and any other files involved (such as
+\c{authorized_keys}, \c{authorized_keys2} or \c{authorization}) are
+not group-writable. You can typically do this by using a command
+such as
+
+\c chmod g-w $HOME $HOME/.ssh $HOME/.ssh/authorized_keys
+
+Your server should now be configured to accept authentication using
+your private key. Now you need to configure PuTTY to \e{attempt}
+authentication using your private key. You can do this in either of
+two ways:
+
+\b Select the private key in PuTTY's configuration. See
+\k{config-ssh-privkey} for details.
+
+\b Load the private key into Pageant (see \k{pageant}). In this case
+PuTTY will automatically try to use it for authentication if it can.
~mdw / sgt / putty / commitdiff