-\versionid $Id: pubkey.but,v 1.19 2002/11/01 21:50:35 jacob Exp $
+\define{versionidpubkey} \versionid $Id$
\C{pubkey} Using public keys for SSH authentication
PuTTYgen later (see \k{puttygen-load}) and the public key will be
available for copying and pasting again.
-\k{pubkey-gettingready} describes the typical process of configuring
+\K{pubkey-gettingready} describes the typical process of configuring
PuTTY to attempt public-key authentication, and configuring your SSH
server to accept it.
which type of key you need. PuTTYgen currently supports three types
of key:
-\b An RSA key for use with the SSH 1 protocol.
+\b An RSA key for use with the SSH-1 protocol.
-\b An RSA key for use with the SSH 2 protocol.
+\b An RSA key for use with the SSH-2 protocol.
-\b A DSA key for use with the SSH 2 protocol.
+\b A DSA key for use with the SSH-2 protocol.
-The SSH 1 protocol only supports RSA keys; if you will be connecting
-using the SSH 1 protocol, you must select the first key type or your
+The SSH-1 protocol only supports RSA keys; if you will be connecting
+using the SSH-1 protocol, you must select the first key type or your
key will be completely useless.
-The SSH 2 protocol supports more than one key type. The two types
+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
Currently 1024 bits should be sufficient for most purposes.
+Note that an RSA key is generated by finding two primes of half the
+length requested, and then multiplying them together. For example,
+if you ask PuTTYgen for a 1024-bit RSA key, it will create two
+512-bit primes and multiply them. The result of this multiplication
+might be 1024 bits long, or it might be only 1023; so you may not
+get the exact length of key you asked for. This is perfectly normal,
+and you do not need to worry. The lengths should only ever differ by
+one, and there is no perceptible drop in security as a result.
+
+DSA keys are not created by multiplying primes together, so they
+should always be exactly the length you asked for.
+
\S{puttygen-generate} The \q{Generate} button
\cfg{winhelp-topic}{puttygen.generate}
box asking you where to save the file. Select a directory, type in a
file name, and press \q{Save}.
-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}).
+This file is in PuTTY's native format (\c{*.PPK}); it 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{puttygen-savepub} Saving your public key to a disk file
\cfg{winhelp-topic}{puttygen.savepub}
-The SSH 2 protocol drafts specify a standard format for storing
+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
+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}.
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
+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
+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
\cfg{winhelp-topic}{puttygen.pastekey}
-All SSH 1 servers require your public key to be given to it in a
+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.
+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
\cfg{winhelp-topic}{puttygen.conversions}
-Most SSH1 clients use a standard format for storing private keys on
+Most SSH-1 clients use a standard format for storing private keys on
disk. PuTTY uses this format as well; so if you have generated an
-SSH1 private key using OpenSSH or \cw{ssh.com}'s client, you can use
+SSH-1 private key using OpenSSH or \cw{ssh.com}'s client, you can use
it with PuTTY, and vice versa.
-However, SSH2 private keys have no standard format. OpenSSH and
+However, SSH-2 private keys have no standard format. OpenSSH and
\cw{ssh.com} have different formats, and PuTTY's is different again.
So a key generated with one client cannot immediately be used with
another.
Using the \q{Import} command from the \q{Conversions} menu, PuTTYgen
-can load SSH2 private keys in OpenSSH's format and \cw{ssh.com}'s
+can load SSH-2 private keys in OpenSSH's format and \cw{ssh.com}'s
format. Once you have loaded one of these key types, you can then
-save it back out as a PuTTY-format key so that you can use it with
-PuTTY. The passphrase will be unchanged by this process (unless you
-deliberately change it). You may want to change the key comment
-before you save the key, since OpenSSH's SSH2 key format contains no
-space for a comment and \cw{ssh.com}'s default comment format is
-long and verbose.
+save it back out as a PuTTY-format key (\c{*.PPK}) so that you can use
+it with the PuTTY suite. The passphrase will be unchanged by this
+process (unless you deliberately change it). You may want to change
+the key comment before you save the key, since OpenSSH's SSH-2 key
+format contains no space for a comment and \cw{ssh.com}'s default
+comment format is long and verbose.
PuTTYgen can also export private keys in OpenSSH format and in
\cw{ssh.com} format. To do so, select one of the \q{Export} options
passphrase in beforehand, and you will be warned if you are about to
save a key without a passphrase.
-Note that since only SSH2 keys come in different formats, the export
-options are not available if you have generated an SSH1 key.
+Note that since only SSH-2 keys come in different formats, the export
+options are not available if you have generated an SSH-1 key.
\H{pubkey-gettingready} Getting ready for public key authentication
password to login. Once logged in, you must configure the server to
accept your public key for authentication:
-\b If your server is using the SSH 1 protocol, you should change
+\b If your server is using the SSH-1 protocol, you should change
into the \c{.ssh} directory and open the file \c{authorized_keys}
with your favourite editor. (You may have to create this file if
this is the first key you have put in it). Then switch 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
+\b If your server is OpenSSH and is using the SSH-2 protocol, you
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.)
+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 (see \k{puttygen-savepub}), and
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
+not group-writable or world-writable. You can typically do this by
+using a command such as
-\c chmod g-w $HOME $HOME/.ssh $HOME/.ssh/authorized_keys
+\c chmod go-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}
~mdw / sgt / putty / blobdiff