Add support for most of the ESC[<low number>t sequences, which xterm
[sgt/putty] / doc / faq.but
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ee46ef84 1\A{faq} PuTTY FAQ
2
3This FAQ is published on the PuTTY web site, and also provided as an
4appendix in the manual.
5
6\H{faq-support} Features supported in PuTTY
7
8In general, if you want to know if PuTTY supports a particular
9feature, you should look for it on the
10\W{http://www.chiark.greenend.org.uk/~sgtatham/putty/}{PuTTY web site}.
11In particular:
12
13\b try the
14\W{http://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html}{changes
15page}, and see if you can find the feature on there. If a feature is
16listed there, it's been implemented. If it's listed as a change made
17\e{since} the latest version, it should be available in the
18development snapshots, in which case testing will be very welcome.
19
20\b try the
21\W{http://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist.html}{Wishlist
22page}, and see if you can find the feature there. If it's on there,
23it probably \e{hasn't} been implemented.
24
70706890 25\S{faq-ssh2}{question} Does PuTTY support SSH v2?
ee46ef84 26
27Yes. SSH v2 support has been available in PuTTY since version 0.50.
28However, currently the \e{default} SSH protocol is v1; to select SSH
29v2 if your server supports both, go to the SSH panel and change the
30\e{Preferred SSH protocol version} option.
31
32Public key authentication (both RSA and DSA) in SSH v2 has been
33added since version 0.51.
34
70706890 35\S{faq-ssh2-keyfmt}{question} Does PuTTY support reading OpenSSH or
ee46ef84 36\cw{ssh.com} SSHv2 private key files?
37
38Not at present. OpenSSH and \cw{ssh.com} have totally different
39formats for private key files, and neither one is particularly
40pleasant, so PuTTY has its own. We do plan to write a converter at
41some stage.
42
70706890 43\S{faq-ssh1}{question} Does PuTTY support SSH v1?
ee46ef84 44
45Yes. SSH 1 support has always been available in PuTTY.
46
70706890 47\S{faq-localecho}{question} Does PuTTY support local echo?
ee46ef84 48
49Yes.
50
51In version 0.51 and before, local echo cannot be separated from
52local line editing (where you type a line of text locally, and it is
53not sent to the server until you press Return, so you have the
54chance to edit it and correct mistakes \e{before} the server sees
55it). The two features can be enabled and disabled from the Terminal
56panel, using the checkbox marked \q{Use local terminal line
57discipline}. Note that due to a bug in those versions of PuTTY,
58changing this feature in mid-session will have no effect; you have
59to enable it \e{before} you open the connection.
60
61In later versions, local echo and local line editing are separate
62options, and by default PuTTY will try to determine automatically
63whether to enable them or not, based on which protocol you have
64selected and also based on hints from the server. If you have a
65problem with PuTTY's default choice, you can force each option to be
66enabled or disabled as you choose. The controls are in the Terminal
67panel, in the section marked \q{Line discipline options}.
68
70706890 69\S{faq-disksettings}{question} Does PuTTY support storing its
70settings in a disk file?
ee46ef84 71
72Not at present, although \k{config-file} in the documentation gives
73a method of achieving the same effect.
74
70706890 75\S{faq-fullscreen}{question} Does PuTTY support full-screen mode,
76like a DOS box?
ee46ef84 77
78Not in the 0.51 release, but it has been added since then.
79
70706890 80\S{faq-password}{question} Does PuTTY have the ability to remember
81my password so I don't have to type it every time?
ee46ef84 82
83No, it doesn't.
84
85Remembering your password is a bad plan for obvious security
86reasons: anyone who gains access to your machine while you're away
87from your desk can find out the remembered password, and use it,
88abuse it or change it.
89
90In addition, it's not even \e{possible} for PuTTY to automatically
91send your password in a Telnet session, because Telnet doesn't give
92the client software any indication of which part of the login
93process is the password prompt. PuTTY would have to guess, by
94looking for words like \q{password} in the session data; and if your
95login program is written in something other than English, this won't
96work.
97
98In SSH, remembering your password would be possible in theory, but
99there doesn't seem to be much point since SSH supports public key
100authentication, which is more flexible and more secure. See
101\k{pubkey} in the documentation for a full discussion of public key
102authentication.
103
70706890 104\S{faq-hostkeys}{question} Is there an option to turn off the
105annoying host key prompts?
cad566a9 106
107No, there isn't. And there won't be. Even if you write it yourself
108and send us the patch, we won't accept it.
109
110Those annoying host key prompts are the \e{whole point} of SSH.
111Without them, all the cryptographic technology SSH uses to secure
112your session is doing nothing more than making an attacker's job
113slightly harder; instead of sitting between you and the server with
114a packet sniffer, the attacker must actually subvert a router and
115start modifying the packets going back and forth. But that's not all
116that much harder than just sniffing; and without host key checking,
117it will go completely undetected by client or server.
118
119Host key checking is your guarantee that the encryption you put on
120your data at the client end is the \e{same} encryption taken off the
121data at the server end; it's your guarantee that it hasn't been
122removed and replaced somewhere on the way. Host key checking makes
123the attacker's job \e{astronomically} hard, compared to packet
124sniffing, and even compared to subverting a router. Instead of
125applying a little intelligence and keeping an eye on Bugtraq, the
126attacker must now perform a brute-force attack against at least one
127military-strength cipher. That insignificant host key prompt really
128does make \e{that} much difference.
129
130If you're having a specific problem with host key checking - perhaps
131you want an automated batch job to make use of PSCP or Plink, and
132the interactive host key prompt is hanging the batch process - then
133the right way to fix it is to add the correct host key to the
134Registry in advance. That way, you retain the \e{important} feature
135of host key checking: the right key will be accepted and the wrong
136ones will not. Adding an option to turn host key checking off
137completely is the wrong solution and we will not do it.
138
70706890 139\S{faq-server}{question} Will you write an SSH server for the PuTTY
140suite, to go with the client?
ae915483 141
142No. The only reason we might want to would be if we could easily
143re-use existing code and significantly cut down the effort. We don't
144believe this is the case; there just isn't enough common ground
145between an SSH client and server to make it worthwhile.
146
147If someone else wants to use bits of PuTTY in the process of writing
148a Windows SSH server, they'd be perfectly welcome to of course, but
149I really can't see it being a lot less effort for us to do that than
150it would be for us to write a server from the ground up. We don't
151have time, and we don't have motivation. The code is available if
152anyone else wants to try it.
153
ee46ef84 154\H{faq-ports} Ports to other operating systems
155
156The eventual goal is for PuTTY to be a multi-platform program, able
157to run on at least Windows, MacOS and Unix. Whether this will
158actually ever happen I have no idea, but it is the plan. A Mac port
159has been started, but is only half-finished and currently not moving
160very fast.
161
162Porting will become easier once PuTTY has a generalised porting
163layer, drawing a clear line between platform-dependent and
164platform-independent code. The general intention is for this porting
165layer to evolve naturally as part of the process of doing the first
166port. One particularly nasty part of this will be separating the
167many configuration options into platform-dependent and
168platform-independent ones; for example, the options controlling when
169the Windows System menu appears will be pretty much meaningless
170under X11 or perhaps other windowing systems, whereas Telnet Passive
171Mode is universal and shouldn't need to be specified once for each
172platform.
173
70706890 174\S{faq-wince}{question} Will there be a port to Windows CE?
ee46ef84 175
176Probably not in the particularly near future. Despite sharing large
177parts of the Windows API, in practice WinCE doesn't appear to be
178significantly easier to port to than a totally different operating
179system.
180
181However, PuTTY on portable devices would clearly be a useful thing,
182so in the long term I hope there will be a WinCE port.
183
70706890 184\S{faq-mac}{question} Will there be a port to the Mac?
ee46ef84 185
186A Mac port was started once and is half-finished, but development
187has been static for some time and the main PuTTY code has moved on,
188so it's not clear how quickly development would resume even if
189developer effort were available.
190
70706890 191\S{faq-unix}{question} Will there be a port to Unix?
ee46ef84 192
193I hope so, if only so that I can have an \cw{xterm}-like program
194that supports exactly the same terminal emulation as PuTTY. If and
195when we do do a Unix port, it will have a local-terminal back end so
196it can be used like an \cw{xterm}, rather than only being usable as
197a network utility.
198
70706890 199\S{faq-epoc}{question} Will there be a port to EPOC?
ee46ef84 200
201I hope so, but given that ports aren't really progressing very fast
202even on systems the developers \e{do} already know how to program
203for, it might be a long time before any of us get round to learning
204a new system and doing the port for that.
205
206\H{faq-embedding} Embedding PuTTY in other programs
207
70706890 208\S{faq-dll}{question} Is the SSH or Telnet code available as a DLL?
ee46ef84 209
210No, it isn't. It would take a reasonable amount of rewriting for
211this to be possible, and since the PuTTY project itself doesn't
212believe in DLLs (they make installation more error-prone) none of us
213has taken the time to do it.
214
215Most of the code cleanup work would be a good thing to happen in
216general, so if anyone feels like helping, we wouldn't say no.
217
70706890 218\S{faq-vb}{question} Is the SSH or Telnet code available as a Visual
219Basic component?
ee46ef84 220
221No, it isn't. None of the PuTTY team uses Visual Basic, and none of
222us has any particular need to make SSH connections from a Visual
223Basic application. In addition, all the preliminary work to turn it
224into a DLL would be necessary first; and furthermore, we don't even
225know how to write VB components.
226
227If someone offers to do some of this work for us, we might consider
228it, but unless that happens I can't see VB integration being
229anywhere other than the very bottom of our priority list.
230
70706890 231\S{faq-ipc}{question} How can I use PuTTY to make an SSH connection
232from within another program?
ee46ef84 233
234Probably your best bet is to use Plink, the command-line connection
235tool. If you can start Plink as a second Windows process, and
236arrange for your primary process to be able to send data to the
237Plink process, and receive data from it, through pipes, then you
238should be able to make SSH connections from your program.
239
240This is what CVS for Windows does, for example.
241
242\H{faq-details} Details of PuTTY's operation
243
70706890 244\S{faq-term}{question} What terminal type does PuTTY use?
ee46ef84 245
246For most purposes, PuTTY can be considered to be an \cw{xterm}
247terminal, although full support for some of \cw{xterm}'s features,
248such as passing mouse actions to the server-side program, is not
249present in the 0.51 release (but has been added since).
250
251PuTTY also supports some terminal control sequences not supported by
252the real \cw{xterm}: notably the Linux console sequences that
253reconfigure the colour palette, and the title bar control sequences
254used by \cw{DECterm} (which are different from the \cw{xterm} ones;
255PuTTY supports both).
256
257By default, PuTTY announces its terminal type to the server as
258\c{xterm}. If you have a problem with this, you can reconfigure it
259to say something else; \c{vt220} might help if you have trouble.
260
70706890 261\S{faq-settings}{question} Where does PuTTY store its data?
ee46ef84 262
263PuTTY stores most of its data (saved sessions, SSH host keys) in the
264Registry. The precise location is
265
266\c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY
267
268and within that area, saved sessions are stored under \c{Sessions}
269while host keys are stored under \c{SshHostKeys}.
270
271PuTTY also requires a random number seed file, to improve the
272unpredictability of randomly chosen data needed as part of the SSH
273cryptography. This is stored by default in your Windows home
274directory (\c{%HOMEDRIVE%\\%HOMEPATH%}), or in the actual Windows
275directory (such as \c{C:\\WINDOWS}) if the home directory doesn't
276exist, for example if you're using Win95. If you want to change the
277location of the random number seed file, you can put your chosen
278pathname in the Registry, at
279
280\c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\RandSeedFile
281
282\H{faq-howto} HOWTO questions
283
70706890 284\S{faq-startmax}{question} How can I make PuTTY start up maximised?
ee46ef84 285
286Create a Windows shortcut to start PuTTY from, and set it as \q{Run
287Maximized}.
288
70706890 289\S{faq-startsess}{question} How can I create a Windows shortcut to
290start a particular saved session directly?
ee46ef84 291
292To run a PuTTY session saved under the name \q{\cw{mysession}},
293create a Windows shortcut that invokes PuTTY with a command line
294like
295
296\c \path\name\to\putty.exe @mysession
297
70706890 298\S{faq-startssh}{question} How can I start an SSH session straight
299from the command line?
ee46ef84 300
301Use the command line \c{putty -ssh host.name}. Alternatively, create
302a saved session that specifies the SSH protocol, and start the saved
303session as shown in \k{faq-startsess}.
304
70706890 305\S{faq-cutpaste}{question} How do I copy and paste between PuTTY and
306other Windows applications?
ee46ef84 307
308Copy and paste works similarly to the X Window System. You use the
309left mouse button to select text in the PuTTY window. The act of
310selection \e{automatically} copies the text to the clipboard: there
311is no need to press Ctrl-Ins or Ctrl-C or anything else. In fact,
312pressing Ctrl-C will send a Ctrl-C character to the other end of
313your connection (just like it does the rest of the time), which may
314have unpleasant effects. The \e{only} thing you need to do, to copy
315text to the clipboard, is to select it.
316
317To paste the clipboard contents into a PuTTY window, by default you
318click the right mouse button. If you have a three-button mouse and
319are used to X applications, you can configure pasting to be done by
320the middle button instead, but this is not the default because most
321Windows users don't have a middle button at all.
322
323You can also paste by pressing Shift-Ins.
324
70706890 325\S{faq-tunnels}{question} How do I use X forwarding and port
326forwarding? I can't find the Tunnels panel.
f2003e32 327
328If you're looking in the 0.51 release or earlier, the Tunnels panel
329isn't there. It was added in the development snapshots after 0.51,
330and releases 0.52 and onwards will contain it.
331
70706890 332\S{faq-options}{question} How do I use all PuTTY's features (public
333keys, port forwarding, SSH v2, etc.) in PSCP, PSFTP and Plink?
72be5b5e 334
335The command-line tools are currently rather short of command line
336options to enable this sort of thing. However, you can use most of
337PuTTY's features if you create a PuTTY saved session, and then use
338the name of the saved session on the command line in place of a
339hostname. This works for PSCP, PSFTP and Plink (but don't expect
340port forwarding in the file transfer applications!).
f2003e32 341
70706890 342\S{faq-pscp}{question} How do I use PSCP.EXE? When I double-click it
343gives me a command prompt window which then closes instantly.
ee46ef84 344
345PSCP is a command-line application, not a GUI application. If you
346run it without arguments, it will simply print a help message and
347terminate.
348
349To use PSCP properly, run it from a Command Prompt window. See
350\k{pscp} in the documentation for more details.
351
70706890 352\S{faq-pscp-spaces}{question} How do I use PSCP to copy a file whose
353name has spaces in?
ee46ef84 354
355If PSCP is using the traditional SCP protocol, this is confusing. If
356you're specifying a file at the local end, you just use one set of
357quotes as you would normally do:
358
359\c pscp "local filename with spaces" user@host:
360\c pscp user@host:myfile "local filename with spaces"
361
362But if the filename you're specifying is on the \e{remote} side, you
363have to use backslashes and two sets of quotes:
364
365\c pscp user@host:"\"remote filename with spaces\"" local_filename
366\c pscp local_filename user@host:"\"remote filename with spaces\""
367
368Worse still, in a remote-to-local copy you have to specify the local
369file name explicitly, otherwise PSCP will complain that they don't
370match (unless you specified the \c{-unsafe} option). The following
371command will give an error message:
372
373\c c:\>pscp user@host:"\"oo er\"" .
e9cee352 374\c warning: remote host tried to write to a file called 'oo er'
375\c when we requested a file called '"oo er"'.
ee46ef84 376
e9cee352 377Instead, you need to specify the local file name in full:
378
379\c c:\>pscp user@host:"\"oo er\"" "oo er"
380
ee46ef84 381If PSCP is using the newer SFTP protocol, none of this is a problem,
382and all filenames with spaces in are specified using a single pair
383of quotes in the obvious way:
384
385\c pscp "local file" user@host:
386\c pscp user@host:"remote file" .
387
388\H{faq-trouble} Troubleshooting
389
70706890 390\S{faq-mac}{question} Why do I see \q{Incorrect MAC received on
391packet}?
ee46ef84 392
393This is due to a bug in old SSH 2 servers distributed by
394\cw{ssh.com}. Version 2.3.0 and below of their SSH 2 server
395constructs Message Authentication Codes in the wrong way, and
396expects the client to construct them in the same wrong way. PuTTY
397constructs the MACs correctly by default, and hence these old
398servers will fail to work with it.
399
400If you are using PuTTY version 0.51 or below, go to the SSH panel
401and check the box labelled \q{Imitate SSH 2 MAC bug}. This will
402cause PuTTY to construct its MACs in the same incorrect manner as
403the buggy servers, so it will be able to work with them.
404
405Since version 0.51, PuTTY has been enhanced to detect buggy servers
406automatically (when they announce their version) and enable the
407workaround without the user needing to ask. Therefore you \e{should}
408never have to use this option again after 0.52, but it is still
409provided just in case another buggy server shows up.
410
b7e2c163 411In this context MAC stands for Message Authentication Code. It's a
412cryptographic term, and it has nothing at all to do with Ethernet
413MAC (Media Access Control) addresses.
414
70706890 415\S{faq-colours}{question} I clicked on a colour in the Colours
416panel, and the colour didn't change in my terminal.
ee46ef84 417
418That isn't how you're supposed to use the Colours panel.
419
420During the course of a session, PuTTY potentially uses \e{all} the
421colours listed in the Colours panel. It's not a question of using
422only one of them and you choosing which one; PuTTY will use them
423\e{all}. The purpose of the Colours panel is to let you adjust the
424appearance of all the colours. So to change the colour of the
425cursor, for example, you would select \q{Cursor Colour}, press the
426\q{Modify} button, and select a new colour from the dialog box that
427appeared. Similarly, if you want your session to appear in green,
428you should select \q{Default Foreground} and press \q{Modify}.
429Clicking on \q{ANSI Green} won't turn your session green; it will
430only allow you to adjust the \e{shade} of green used when PuTTY is
431instructed by the server to display green text.
432
70706890 433\S{faq-winsock2}{question} Plink on Windows 95 says it can't find
434\cw{WS2_32.DLL}.
ee46ef84 435
436Plink requires the extended Windows network library, WinSock version
4372. This is installed as standard on Windows 98 and above, and on
438Windows NT, and even on later versions of Windows 95; but early
439Win95 installations don't have it.
440
441In order to use Plink on these systems, you will need to download
442the
443\W{http://www.microsoft.com/windows95/downloads/contents/wuadmintools/s_wunetworkingtools/w95sockets2/}{WinSock 2 upgrade}:
444
445\c http://www.microsoft.com/windows95/downloads/contents/wuadmintools/
446\c s_wunetworkingtools/w95sockets2/
447
70706890 448\S{faq-rekey}{question} My PuTTY sessions close after an hour and
449tell me \q{Server failed host key check}.
ee46ef84 450
451This is a bug in all versions of PuTTY up to and including 0.51. SSH
452v2 servers from \cw{ssh.com} will require the key exchange to be
453repeated one hour after the start of the connection, and PuTTY will
454get this wrong.
455
456The bug has been fixed since version 0.51, so upgrading to a later
457version or snapshot should solve the problem.
458
70706890 459\S{faq-outofmem}{question} After trying to establish an SSH 2
460connection, PuTTY says \q{Out of memory} and dies.
ee46ef84 461
462If this happens just while the connection is starting up, this often
463indicates that for some reason the client and server have failed to
464establish a session encryption key. Somehow, they have performed
465calculations that should have given each of them the same key, but
466have ended up with different keys; so data encrypted by one and
467decrypted by the other looks like random garbage.
468
469This causes an \q{out of memory} error because the first encrypted
470data PuTTY expects to see is the length of an SSH message. Normally
471this will be something well under 100 bytes. If the decryption has
472failed, PuTTY will see a completely random length in the region of
473two \e{gigabytes}, and will try to allocate enough memory to store
474this non-existent message. This will immediately lead to it thinking
475it doesn't have enough memory, and panicking.
476
477If this happens to you, it is quite likely to still be a PuTTY bug
478and you should report it (although it might be a bug in your SSH
479server instead); but it doesn't necessarily mean you've actually run
480out of memory.
481
70706890 482\S{faq-bce}{question} When I run full-colour applications, I see
483areas of black space where colour ought to be.
f1453e5c 484
485You almost certainly need to enable the \q{Use background colour to
486erase screen} setting in the Terminal panel. Note that if you do
487this in mid-session, it won't take effect until you reset the
488terminal (see \k{faq-resetterm}).
489
70706890 490\S{faq-resetterm}{question} When I change some terminal settings,
491nothing happens.
f1453e5c 492
493Some of the terminal options (notably Auto Wrap and
494background-colour screen erase) actually represent the \e{default}
495setting, rather than the currently active setting. The server can
496send sequences that modify these options in mid-session, but when
497the terminal is reset (by server action, or by you choosing \q{Reset
498Terminal} from the System menu) the defaults are restored.
499
500If you want to change one of these options in the middle of a
501session, you will find that the change does not immediately take
502effect. It will only take effect once you reset the terminal.
503
70706890 504\S{faq-altgr}{question} I can't type characters that require the
505AltGr key.
ee46ef84 506
507In PuTTY version 0.51, the AltGr key was broken. The bug has been
508fixed since then.
509
70706890 510\S{faq-idleout}{question} My PuTTY sessions unexpectedly close after
511they are idle for a while.
ee46ef84 512
513Some types of firewall, and almost any router doing Network Address
514Translation (NAT, also known as IP masquerading), will forget about
515a connection through them if the connection does nothing for too
516long. This will cause the connection to be rudely cut off when
517contact is resumed.
518
519You can try to combat this by telling PuTTY to send \e{keepalives}:
520packets of data which have no effect on the actual session, but
521which reassure the router or firewall that the network connection is
522still active and worth remembering about.
523
524Keepalives don't solve everything, unfortunately; although they
525cause greater robustness against this sort of router, they can also
526cause a \e{loss} of robustness against network dropouts. See
527\k{config-keepalive} in the documentation for more discussion of
528this.
529
70706890 530\S{faq-timeout}{question} PuTTY's network connections time out too
531quickly when network connectivity is temporarily lost.
ee46ef84 532
533This is a Windows problem, not a PuTTY problem. The timeout value
534can't be set on per application or per session basis. To increase
535the TCP timeout globally, you need to tinker with the Registry.
536
537On Windows 95, 98 or ME, the registry key you need to change is
538
539\c HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\
540\c MSTCP\MaxDataRetries
541
542(it must be of type DWORD in Win95, or String in Win98/ME).
543
544On Windows NT or 2000, the registry key is
545
546\c HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\
547\c Parameters\TcpMaxDataRetransmissions
548
549and it must be of type DWORD.
550
551Set the key's value to something like 10. This will cause Windows to
552try harder to keep connections alive instead of abandoning them.
553
70706890 554\S{faq-puttyputty}{question} When I \cw{cat} a binary file, I get
ee46ef84 555`PuTTYPuTTYPuTTY' on my command line.
556
557Don't \cw{cat} binary files, then.
558
559This is designed behaviour; when PuTTY receives the character
560Control-E from the remote server, it interprets it as a request to
561identify itself, and so it sends back the string \q{\cw{PuTTY}} as
562if that string had been entered at the keyboard. Control-E should
563only be sent by programs that are prepared to deal with the
564response. Writing a binary file to your terminal is likely to output
565many Control-E characters, and cause this behaviour. Don't do it.
566It's a bad plan.
567
70706890 568\S{faq-puttyputty}{question} When I \cw{cat} a binary file, my
569window title changes to a nonsense string.
ee46ef84 570
571Don't \cw{cat} binary files, then.
572
573It is designed behaviour that PuTTY should have the ability to
574adjust the window title on instructions from the server. Normally
575the control sequence that does this should only be sent
576deliberately, by programs that know what they are doing and intend
577to put meaningful text in the window title. Writing a binary file to
578your terminal runs the risk of sending the same control sequence by
579accident, and cause unexpected changes in the window title. Don't do
580it.
581
70706890 582\S{faq-password}{question} My keyboard stops working once PuTTY
583displays the password prompt.
59c1f1f6 584
585No, it doesn't. PuTTY just doesn't display the password you type, so
586that someone looking at your screen can't see what it is.
587
588Unlike the Windows login prompts, PuTTY doesn't display the password
589as a row of asterisks either. This is so that someone looking at
590your screen can't even tell how \e{long} your password is, which
591might be valuable information.
592
ee46ef84 593\H{faq-secure} Security questions
594
70706890 595\S{faq-publicpc}{question} Is it safe for me to download PuTTY and
596use it on a public PC?
ee46ef84 597
598It depends on whether you trust that PC. If you don't trust the
599public PC, don't use PuTTY on it, and don't use any other software
600you plan to type passwords into either. It might be watching your
601keystrokes, or it might tamper with the PuTTY binary you download.
602There is \e{no} program safe enough that you can run it on an
603actively malicious PC and get away with typing passwords into it.
604
605If you do trust the PC, then it's probably OK to use PuTTY on it
606(but if you don't trust the network, then the PuTTY download might
607be tampered with, so it would be better to carry PuTTY with you on a
608floppy).
609
70706890 610\S{faq-cleanup}{question} What does PuTTY leave on a system? How can
611I clean up after it?
ee46ef84 612
613PuTTY will leave some Registry entries, and a random seed file, on
614the PC (see \k{faq-settings}). If you are using PuTTY on a public
615PC, or somebody else's PC, you might want to clean these up when you
616leave. You can do that automatically, by running the command
617\c{putty -cleanup}.
618
70706890 619\S{faq-dsa}{question} How come PuTTY now supports DSA, when the
620website used to say how insecure it was?
ee46ef84 621
622DSA has a major weakness \e{if badly implemented}: it relies on a
623random number generator to far too great an extent. If the random
624number generator produces a number an attacker can predict, the DSA
625private key is exposed - meaning that the attacker can log in as you
626on all systems that accept that key.
627
628The PuTTY policy changed because the developers were informed of
629ways to implement DSA which do not suffer nearly as badly from this
630weakness, and indeed which don't need to rely on random numbers at
631all. For this reason we now believe PuTTY's DSA implementation is
632probably OK. However, if you have the choice, we still recommend you
633use RSA instead.
634
635\H{faq-admin} Administrative questions
636
70706890 637\S{faq-domain}{question} Would you like me to register you a nicer
638domain name?
ee46ef84 639
640No, thank you. Even if you can find one (most of them seem to have
641been registered already, by people who didn't ask whether we
642actually wanted it before they applied), we're happy with the PuTTY
643web site being exactly where it is. It's not hard to find (just type
644\q{putty} into \W{http://www.google.com/}{google.com} and we're the
645first link returned), and we don't believe the administrative hassle
646of moving the site would be worth the benefit.
647
648In addition, if we \e{did} want a custom domain name, we would want
649to run it ourselves, so we knew for certain that it would continue
650to point where we wanted it, and wouldn't suddenly change or do
651strange things. Having it registered for us by a third party who we
652don't even know is not the best way to achieve this.
653
70706890 654\S{faq-webhosting}{question} Would you like free web hosting for the
655PuTTY web site?
ee46ef84 656
657We already have some, thanks.
658
70706890 659\S{faq-sourceforge}{question} Why don't you move PuTTY to
660SourceForge?
ee46ef84 661
662Partly, because we don't want to move the web site location (see
663\k{faq-domain}).
664
665Also, security reasons. PuTTY is a security product, and as such it
666is particularly important to guard the code and the web site against
667unauthorised modifications which might introduce subtle security
668flaws. Therefore, we prefer that the CVS repository, web site and
669FTP site remain where they are, under the direct control of system
670administrators we know and trust personally, rather than being run
671by a large organisation full of people we've never met and which is
672known to have had breakins in the past.
673
674No offence to SourceForge; I think they do a wonderful job. But
675they're not ideal for everyone, and in particular they're not ideal
676for us.
677
70706890 678\S{faq-mailinglist1}{question} Why can't I subscribe to the
679putty-bugs mailing list?
ee46ef84 680
681Because you're not a member of the PuTTY core development team. The
682putty-bugs mailing list is not a general newsgroup-like discussion
683forum; it's a contact address for the core developers, and an
684\e{internal} mailing list for us to discuss things among ourselves.
685If we opened it up for everybody to subscribe to, it would turn into
686something more like a newsgroup and we would be completely
687overwhelmed by the volume of traffic. It's hard enough to keep up
688with the list as it is.
689
70706890 690\S{faq-mailinglist2}{question} If putty-bugs isn't a
691general-subscription mailing list, what is?
ee46ef84 692
693There isn't one, that we know of.
694
695If someone else wants to set up a mailing list for PuTTY users to
696help each other with common problems, that would be fine with us;
697but the PuTTY team would almost certainly not have the time to read
698it, so any questions the list couldn't answer would have to be
699forwarded on to us by the questioner. In any case, it's probably
700better to use the established newsgroup \cw{comp.security.ssh} for
701this purpose.
702
70706890 703\S{faq-donations}{question} How can I donate to PuTTY development?
ee46ef84 704
705Please, \e{please} don't feel you have to. PuTTY is completely free
706software, and not shareware. We think it's very important that
707\e{everybody} who wants to use PuTTY should be able to, whether they
708have any money or not; so the last thing we would want is for a
709PuTTY user to feel guilty because they haven't paid us any money. If
710you want to keep your money, please do keep it. We wouldn't dream of
711asking for any.
712
713Having said all that, if you still really \e{want} to give us money,
714we won't argue :-) The easiest way for us to accept donations is if
715you go to \W{http://www.e-gold.com}\cw{www.e-gold.com}, and deposit
716your donation in account number 174769. Then send us e-mail to let
717us know you've done so (otherwise we might not notice for months!).
718
719Small donations (tens of dollars or tens of euros) will probably be
720spent on beer or curry, which helps motivate our volunteer team to
721continue doing this for the world. Larger donations will be spent on
722something that actually helps development, if we can find anything
723(perhaps new hardware, or a copy of Windows 2000), but if we can't
724find anything then we'll just distribute the money among the
725developers. If you want to be sure your donation is going towards
726something worthwhile, ask us first. If you don't like these terms,
727feel perfectly free not to donate. We don't mind.
728
70706890 729\S{faq-pronounce}{question} How do I pronounce PuTTY?
ee46ef84 730
731Exactly like the normal word \q{putty}. Just like the stuff you put
732on window frames. (One of the reasons it's called PuTTY is because
733it makes Windows usable. :-)