| 1 | \define{versionidpageant} \versionid $Id$ |
| 2 | |
| 3 | \C{pageant} Using \i{Pageant} for authentication |
| 4 | |
| 5 | \cfg{winhelp-topic}{pageant.general} |
| 6 | |
| 7 | Pageant is an SSH \i{authentication agent}. It holds your \i{private key}s |
| 8 | in memory, already decoded, so that you can use them often |
| 9 | \I{passwordless login}without needing to type a \i{passphrase}. |
| 10 | |
| 11 | \H{pageant-start} Getting started with Pageant |
| 12 | |
| 13 | Before you run Pageant, you need to have a private key in \c{*.\i{PPK}} |
| 14 | format. See \k{pubkey} to find out how to generate and use one. |
| 15 | |
| 16 | When you run Pageant, it will put an icon of a computer wearing a |
| 17 | hat into the \ii{System tray}. It will then sit and do nothing, until you |
| 18 | load a private key into it. |
| 19 | |
| 20 | If you click the Pageant icon with the right mouse button, you will |
| 21 | see a menu. Select \q{View Keys} from this menu. The Pageant main |
| 22 | window will appear. (You can also bring this window up by |
| 23 | double-clicking on the Pageant icon.) |
| 24 | |
| 25 | The Pageant window contains a list box. This shows the private keys |
| 26 | Pageant is holding. When you start Pageant, it has no keys, so the |
| 27 | list box will be empty. After you add one or more keys, they will |
| 28 | show up in the list box. |
| 29 | |
| 30 | To add a key to Pageant, press the \q{Add Key} button. Pageant will |
| 31 | bring up a file dialog, labelled \q{Select Private Key File}. Find |
| 32 | your private key file in this dialog, and press \q{Open}. |
| 33 | |
| 34 | Pageant will now load the private key. If the key is protected by a |
| 35 | passphrase, Pageant will ask you to type the passphrase. When the |
| 36 | key has been loaded, it will appear in the list in the Pageant |
| 37 | window. |
| 38 | |
| 39 | Now start PuTTY and open an SSH session to a site that accepts your |
| 40 | key. PuTTY will notice that Pageant is running, retrieve the key |
| 41 | automatically from Pageant, and use it to authenticate. You can now |
| 42 | open as many PuTTY sessions as you like without having to type your |
| 43 | passphrase again. |
| 44 | |
| 45 | (PuTTY can be configured not to try to use Pageant, but it will try |
| 46 | by default. See \k{config-ssh-tryagent} and |
| 47 | \k{using-cmdline-agentauth} for more information.) |
| 48 | |
| 49 | When you want to shut down Pageant, click the right button on the |
| 50 | Pageant icon in the System tray, and select \q{Exit} from the menu. |
| 51 | Closing the Pageant main window does \e{not} shut down Pageant. |
| 52 | |
| 53 | \H{pageant-mainwin} The Pageant main window |
| 54 | |
| 55 | The Pageant main window appears when you left-click on the Pageant |
| 56 | system tray icon, or alternatively right-click and select \q{View |
| 57 | Keys} from the menu. You can use it to keep track of what keys are |
| 58 | currently loaded into Pageant, and to add new ones or remove the |
| 59 | existing keys. |
| 60 | |
| 61 | \S{pageant-mainwin-keylist} The key list box |
| 62 | |
| 63 | \cfg{winhelp-topic}{pageant.keylist} |
| 64 | |
| 65 | The large list box in the Pageant main window lists the private keys |
| 66 | that are currently loaded into Pageant. The list might look |
| 67 | something like this: |
| 68 | |
| 69 | \c ssh1 1024 22:c3:68:3b:09:41:36:c3:39:83:91:ae:71:b2:0f:04 k1 |
| 70 | \c ssh-rsa 1023 74:63:08:82:95:75:e1:7c:33:31:bb:cb:00:c0:89:8b k2 |
| 71 | |
| 72 | For each key, the list box will tell you: |
| 73 | |
| 74 | \b The type of the key. Currently, this can be \c{ssh1} (an RSA key |
| 75 | for use with the SSH-1 protocol), \c{ssh-rsa} (an RSA key for use |
| 76 | with the SSH-2 protocol), or \c{ssh-dss} (a DSA key for use with |
| 77 | the SSH-2 protocol). |
| 78 | |
| 79 | \b The size (in bits) of the key. |
| 80 | |
| 81 | \b The \I{key fingerprint}fingerprint for the public key. This should be |
| 82 | the same fingerprint given by PuTTYgen, and (hopefully) also the same |
| 83 | fingerprint shown by remote utilities such as \i\c{ssh-keygen} when |
| 84 | applied to your \c{authorized_keys} file. |
| 85 | |
| 86 | \b The comment attached to the key. |
| 87 | |
| 88 | \S{pageant-mainwin-addkey} The \q{Add Key} button |
| 89 | |
| 90 | \cfg{winhelp-topic}{pageant.addkey} |
| 91 | |
| 92 | To add a key to Pageant by reading it out of a local disk file, |
| 93 | press the \q{Add Key} button in the Pageant main window, or |
| 94 | alternatively right-click on the Pageant icon in the system tray and |
| 95 | select \q{Add Key} from there. |
| 96 | |
| 97 | Pageant will bring up a file dialog, labelled \q{Select Private Key |
| 98 | File}. Find your private key file in this dialog, and press |
| 99 | \q{Open}. If you want to add more than one key at once, you can |
| 100 | select multiple files using Shift-click (to select several adjacent |
| 101 | files) or Ctrl-click (to select non-adjacent files). |
| 102 | |
| 103 | Pageant will now load the private key(s). If a key is protected by a |
| 104 | passphrase, Pageant will ask you to type the passphrase. |
| 105 | |
| 106 | (This is not the only way to add a private key to Pageant. You can |
| 107 | also add one from a remote system by using agent forwarding; see |
| 108 | \k{pageant-forward} for details.) |
| 109 | |
| 110 | \S{pageant-mainwin-remkey} The \q{Remove Key} button |
| 111 | |
| 112 | \cfg{winhelp-topic}{pageant.remkey} |
| 113 | |
| 114 | If you need to remove a key from Pageant, select that key in the |
| 115 | list box, and press the \q{Remove Key} button. Pageant will remove |
| 116 | the key from its memory. |
| 117 | |
| 118 | You can apply this to keys you added using the \q{Add Key} button, |
| 119 | or to keys you added remotely using agent forwarding (see |
| 120 | \k{pageant-forward}); it makes no difference. |
| 121 | |
| 122 | \H{pageant-cmdline} The Pageant command line |
| 123 | |
| 124 | Pageant can be made to do things automatically when it starts up, by |
| 125 | \I{command-line arguments}specifying instructions on its command line. |
| 126 | If you're starting Pageant from the Windows GUI, you can arrange this |
| 127 | by editing the properties of the \i{Windows shortcut} that it was |
| 128 | started from. |
| 129 | |
| 130 | If Pageant is already running, invoking it again with the options |
| 131 | below causes actions to be performed with the existing instance, not a |
| 132 | new one. |
| 133 | |
| 134 | \S{pageant-cmdline-loadkey} Making Pageant automatically load keys |
| 135 | on startup |
| 136 | |
| 137 | Pageant can automatically load one or more private keys when it |
| 138 | starts up, if you provide them on the Pageant command line. Your |
| 139 | command line might then look like: |
| 140 | |
| 141 | \c C:\PuTTY\pageant.exe d:\main.ppk d:\secondary.ppk |
| 142 | |
| 143 | If the keys are stored encrypted, Pageant will request the |
| 144 | passphrases on startup. |
| 145 | |
| 146 | If Pageant is already running, this syntax loads keys into the |
| 147 | existing Pageant. |
| 148 | |
| 149 | \S{pageant-cmdline-command} Making Pageant run another program |
| 150 | |
| 151 | You can arrange for Pageant to start another program once it has |
| 152 | initialised itself and loaded any keys specified on its command |
| 153 | line. This program (perhaps a PuTTY, or a WinCVS making use of |
| 154 | Plink, or whatever) will then be able to use the keys Pageant has |
| 155 | loaded. |
| 156 | |
| 157 | You do this by specifying the \I{-c-pageant}\c{-c} option followed |
| 158 | by the command, like this: |
| 159 | |
| 160 | \c C:\PuTTY\pageant.exe d:\main.ppk -c C:\PuTTY\putty.exe |
| 161 | |
| 162 | \H{pageant-forward} Using \i{agent forwarding} |
| 163 | |
| 164 | Agent forwarding is a mechanism that allows applications on your SSH |
| 165 | server machine to talk to the agent on your client machine. |
| 166 | |
| 167 | Note that at present, agent forwarding in SSH-2 is only available |
| 168 | when your SSH server is \i{OpenSSH}. The \i\cw{ssh.com} server uses a |
| 169 | different agent protocol, which PuTTY does not yet support. |
| 170 | |
| 171 | To enable agent forwarding, first start Pageant. Then set up a PuTTY |
| 172 | SSH session in which \q{Allow agent forwarding} is enabled (see |
| 173 | \k{config-ssh-agentfwd}). Open the session as normal. (Alternatively, |
| 174 | you can use the \c{-A} command line option; see |
| 175 | \k{using-cmdline-agent} for details.) |
| 176 | |
| 177 | If this has worked, your applications on the server should now have |
| 178 | access to a Unix domain socket which the SSH server will forward |
| 179 | back to PuTTY, and PuTTY will forward on to the agent. To check that |
| 180 | this has actually happened, you can try this command on Unix server |
| 181 | machines: |
| 182 | |
| 183 | \c unixbox:~$ echo $SSH_AUTH_SOCK |
| 184 | \c /tmp/ssh-XXNP18Jz/agent.28794 |
| 185 | \c unixbox:~$ |
| 186 | |
| 187 | If the result line comes up blank, agent forwarding has not been |
| 188 | enabled at all. |
| 189 | |
| 190 | Now if you run \c{ssh} on the server and use it to connect through |
| 191 | to another server that accepts one of the keys in Pageant, you |
| 192 | should be able to log in without a password: |
| 193 | |
| 194 | \c unixbox:~$ ssh -v otherunixbox |
| 195 | \c [...] |
| 196 | \c debug: next auth method to try is publickey |
| 197 | \c debug: userauth_pubkey_agent: trying agent key my-putty-key |
| 198 | \c debug: ssh-userauth2 successful: method publickey |
| 199 | \c [...] |
| 200 | |
| 201 | If you enable agent forwarding on \e{that} SSH connection as well |
| 202 | (see the manual for your server-side SSH client to find out how to |
| 203 | do this), your authentication keys will still be available on the |
| 204 | next machine you connect to - two SSH connections away from where |
| 205 | they're actually stored. |
| 206 | |
| 207 | In addition, if you have a private key on one of the SSH servers, |
| 208 | you can send it all the way back to Pageant using the local |
| 209 | \i\c{ssh-add} command: |
| 210 | |
| 211 | \c unixbox:~$ ssh-add ~/.ssh/id_rsa |
| 212 | \c Need passphrase for /home/fred/.ssh/id_rsa |
| 213 | \c Enter passphrase for /home/fred/.ssh/id_rsa: |
| 214 | \c Identity added: /home/fred/.ssh/id_rsa (/home/simon/.ssh/id_rsa) |
| 215 | \c unixbox:~$ |
| 216 | |
| 217 | and then it's available to every machine that has agent forwarding |
| 218 | available (not just the ones downstream of the place you added it). |
| 219 | |
| 220 | \H{pageant-security} Security considerations |
| 221 | |
| 222 | \I{security risk}Using Pageant for public-key authentication gives you the |
| 223 | convenience of being able to open multiple SSH sessions without |
| 224 | having to type a passphrase every time, but also gives you the |
| 225 | security benefit of never storing a decrypted private key on disk. |
| 226 | Many people feel this is a good compromise between security and |
| 227 | convenience. |
| 228 | |
| 229 | It \e{is} a compromise, however. Holding your decrypted private keys |
| 230 | in Pageant is better than storing them in easy-to-find disk files, |
| 231 | but still less secure than not storing them anywhere at all. This is |
| 232 | for two reasons: |
| 233 | |
| 234 | \b Windows unfortunately provides no way to protect pieces of memory |
| 235 | from being written to the system \i{swap file}. So if Pageant is holding |
| 236 | your private keys for a long period of time, it's possible that |
| 237 | decrypted private key data may be written to the system swap file, |
| 238 | and an attacker who gained access to your hard disk later on might |
| 239 | be able to recover that data. (However, if you stored an unencrypted |
| 240 | key in a disk file they would \e{certainly} be able to recover it.) |
| 241 | |
| 242 | \b Although, like most modern operating systems, Windows prevents |
| 243 | programs from accidentally accessing one another's memory space, it |
| 244 | does allow programs to access one another's memory space |
| 245 | deliberately, for special purposes such as debugging. This means |
| 246 | that if you allow a virus, trojan, or other malicious program on to |
| 247 | your Windows system while Pageant is running, it could access the |
| 248 | memory of the Pageant process, extract your decrypted authentication |
| 249 | keys, and send them back to its master. |
| 250 | |
| 251 | Similarly, use of agent \e{forwarding} is a security improvement on |
| 252 | other methods of one-touch authentication, but not perfect. Holding |
| 253 | your keys in Pageant on your Windows box has a security advantage |
| 254 | over holding them on the remote server machine itself (either in an |
| 255 | agent or just unencrypted on disk), because if the server machine |
| 256 | ever sees your unencrypted private key then the sysadmin or anyone |
| 257 | who cracks the machine can steal the keys and pretend to be you for |
| 258 | as long as they want. |
| 259 | |
| 260 | However, the sysadmin of the server machine can always pretend to be |
| 261 | you \e{on that machine}. So if you forward your agent to a server |
| 262 | machine, then the sysadmin of that machine can access the forwarded |
| 263 | agent connection and request signatures from your private keys, and |
| 264 | can therefore log in to other machines as you. They can only do this |
| 265 | to a limited extent - when the agent forwarding disappears they lose |
| 266 | the ability - but using Pageant doesn't actually \e{prevent} the |
| 267 | sysadmin (or hackers) on the server from doing this. |
| 268 | |
| 269 | Therefore, if you don't trust the sysadmin of a server machine, you |
| 270 | should \e{never} use agent forwarding to that machine. (Of course |
| 271 | you also shouldn't store private keys on that machine, type |
| 272 | passphrases into it, or log into other machines from it in any way |
| 273 | at all; Pageant is hardly unique in this respect.) |