Now that Buttress can spot duplicate section keywords, it turns out
[u/mdw/putty] / doc / faq.but
1 \versionid $Id: faq.but,v 1.14 2001/12/14 12:48:24 simon Exp $
2
3 \A{faq} PuTTY FAQ
4
5 This FAQ is published on the PuTTY web site, and also provided as an
6 appendix in the manual.
7
8 \H{faq-support} Features supported in PuTTY
9
10 In general, if you want to know if PuTTY supports a particular
11 feature, you should look for it on the
12 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/}{PuTTY web site}.
13 In particular:
14
15 \b try the
16 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html}{changes
17 page}, and see if you can find the feature on there. If a feature is
18 listed there, it's been implemented. If it's listed as a change made
19 \e{since} the latest version, it should be available in the
20 development snapshots, in which case testing will be very welcome.
21
22 \b try the
23 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist.html}{Wishlist
24 page}, and see if you can find the feature there. If it's on there,
25 it probably \e{hasn't} been implemented.
26
27 \S{faq-ssh2}{Question} Does PuTTY support SSH v2?
28
29 Yes. SSH v2 support has been available in PuTTY since version 0.50.
30 However, currently the \e{default} SSH protocol is v1; to select SSH
31 v2 if your server supports both, go to the SSH panel and change the
32 \e{Preferred SSH protocol version} option.
33
34 Public key authentication (both RSA and DSA) in SSH v2 has been
35 added since version 0.51.
36
37 \S{faq-ssh2-keyfmt}{Question} Does PuTTY support reading OpenSSH or
38 \cw{ssh.com} SSHv2 private key files?
39
40 Not at present. OpenSSH and \cw{ssh.com} have totally different
41 formats for private key files, and neither one is particularly
42 pleasant, so PuTTY has its own. We do plan to write a converter at
43 some stage.
44
45 \S{faq-ssh1}{Question} Does PuTTY support SSH v1?
46
47 Yes. SSH 1 support has always been available in PuTTY.
48
49 \S{faq-localecho}{Question} Does PuTTY support local echo?
50
51 Yes.
52
53 In version 0.51 and before, local echo cannot be separated from
54 local line editing (where you type a line of text locally, and it is
55 not sent to the server until you press Return, so you have the
56 chance to edit it and correct mistakes \e{before} the server sees
57 it). The two features can be enabled and disabled from the Terminal
58 panel, using the checkbox marked \q{Use local terminal line
59 discipline}. Note that due to a bug in those versions of PuTTY,
60 changing this feature in mid-session will have no effect; you have
61 to enable it \e{before} you open the connection.
62
63 In later versions, local echo and local line editing are separate
64 options, and by default PuTTY will try to determine automatically
65 whether to enable them or not, based on which protocol you have
66 selected and also based on hints from the server. If you have a
67 problem with PuTTY's default choice, you can force each option to be
68 enabled or disabled as you choose. The controls are in the Terminal
69 panel, in the section marked \q{Line discipline options}.
70
71 \S{faq-disksettings}{Question} Does PuTTY support storing its
72 settings in a disk file?
73
74 Not at present, although \k{config-file} in the documentation gives
75 a method of achieving the same effect.
76
77 \S{faq-fullscreen}{Question} Does PuTTY support full-screen mode,
78 like a DOS box?
79
80 Not in the 0.51 release, but it has been added since then.
81
82 \S{faq-password-remember}{Question} Does PuTTY have the ability to
83 remember my password so I don't have to type it every time?
84
85 No, it doesn't.
86
87 Remembering your password is a bad plan for obvious security
88 reasons: anyone who gains access to your machine while you're away
89 from your desk can find out the remembered password, and use it,
90 abuse it or change it.
91
92 In addition, it's not even \e{possible} for PuTTY to automatically
93 send your password in a Telnet session, because Telnet doesn't give
94 the client software any indication of which part of the login
95 process is the password prompt. PuTTY would have to guess, by
96 looking for words like \q{password} in the session data; and if your
97 login program is written in something other than English, this won't
98 work.
99
100 In SSH, remembering your password would be possible in theory, but
101 there doesn't seem to be much point since SSH supports public key
102 authentication, which is more flexible and more secure. See
103 \k{pubkey} in the documentation for a full discussion of public key
104 authentication.
105
106 \S{faq-hostkeys}{Question} Is there an option to turn off the
107 annoying host key prompts?
108
109 No, there isn't. And there won't be. Even if you write it yourself
110 and send us the patch, we won't accept it.
111
112 Those annoying host key prompts are the \e{whole point} of SSH.
113 Without them, all the cryptographic technology SSH uses to secure
114 your session is doing nothing more than making an attacker's job
115 slightly harder; instead of sitting between you and the server with
116 a packet sniffer, the attacker must actually subvert a router and
117 start modifying the packets going back and forth. But that's not all
118 that much harder than just sniffing; and without host key checking,
119 it will go completely undetected by client or server.
120
121 Host key checking is your guarantee that the encryption you put on
122 your data at the client end is the \e{same} encryption taken off the
123 data at the server end; it's your guarantee that it hasn't been
124 removed and replaced somewhere on the way. Host key checking makes
125 the attacker's job \e{astronomically} hard, compared to packet
126 sniffing, and even compared to subverting a router. Instead of
127 applying a little intelligence and keeping an eye on Bugtraq, the
128 attacker must now perform a brute-force attack against at least one
129 military-strength cipher. That insignificant host key prompt really
130 does make \e{that} much difference.
131
132 If you're having a specific problem with host key checking - perhaps
133 you want an automated batch job to make use of PSCP or Plink, and
134 the interactive host key prompt is hanging the batch process - then
135 the right way to fix it is to add the correct host key to the
136 Registry in advance. That way, you retain the \e{important} feature
137 of host key checking: the right key will be accepted and the wrong
138 ones will not. Adding an option to turn host key checking off
139 completely is the wrong solution and we will not do it.
140
141 \S{faq-server}{Question} Will you write an SSH server for the PuTTY
142 suite, to go with the client?
143
144 No. The only reason we might want to would be if we could easily
145 re-use existing code and significantly cut down the effort. We don't
146 believe this is the case; there just isn't enough common ground
147 between an SSH client and server to make it worthwhile.
148
149 If someone else wants to use bits of PuTTY in the process of writing
150 a Windows SSH server, they'd be perfectly welcome to of course, but
151 I really can't see it being a lot less effort for us to do that than
152 it would be for us to write a server from the ground up. We don't
153 have time, and we don't have motivation. The code is available if
154 anyone else wants to try it.
155
156 \H{faq-ports} Ports to other operating systems
157
158 The eventual goal is for PuTTY to be a multi-platform program, able
159 to run on at least Windows, MacOS and Unix. Whether this will
160 actually ever happen I have no idea, but it is the plan. A Mac port
161 has been started, but is only half-finished and currently not moving
162 very fast.
163
164 Porting will become easier once PuTTY has a generalised porting
165 layer, drawing a clear line between platform-dependent and
166 platform-independent code. The general intention is for this porting
167 layer to evolve naturally as part of the process of doing the first
168 port. One particularly nasty part of this will be separating the
169 many configuration options into platform-dependent and
170 platform-independent ones; for example, the options controlling when
171 the Windows System menu appears will be pretty much meaningless
172 under X11 or perhaps other windowing systems, whereas Telnet Passive
173 Mode is universal and shouldn't need to be specified once for each
174 platform.
175
176 \S{faq-wince}{Question} Will there be a port to Windows CE?
177
178 Probably not in the particularly near future. Despite sharing large
179 parts of the Windows API, in practice WinCE doesn't appear to be
180 significantly easier to port to than a totally different operating
181 system.
182
183 However, PuTTY on portable devices would clearly be a useful thing,
184 so in the long term I hope there will be a WinCE port.
185
186 \S{faq-mac-port}{Question} Will there be a port to the Mac?
187
188 A Mac port was started once and is half-finished, but development
189 has been static for some time and the main PuTTY code has moved on,
190 so it's not clear how quickly development would resume even if
191 developer effort were available.
192
193 \S{faq-unix}{Question} Will there be a port to Unix?
194
195 I hope so, if only so that I can have an \cw{xterm}-like program
196 that supports exactly the same terminal emulation as PuTTY. If and
197 when we do do a Unix port, it will have a local-terminal back end so
198 it can be used like an \cw{xterm}, rather than only being usable as
199 a network utility.
200
201 \S{faq-epoc}{Question} Will there be a port to EPOC?
202
203 I hope so, but given that ports aren't really progressing very fast
204 even on systems the developers \e{do} already know how to program
205 for, it might be a long time before any of us get round to learning
206 a new system and doing the port for that.
207
208 \H{faq-embedding} Embedding PuTTY in other programs
209
210 \S{faq-dll}{Question} Is the SSH or Telnet code available as a DLL?
211
212 No, it isn't. It would take a reasonable amount of rewriting for
213 this to be possible, and since the PuTTY project itself doesn't
214 believe in DLLs (they make installation more error-prone) none of us
215 has taken the time to do it.
216
217 Most of the code cleanup work would be a good thing to happen in
218 general, so if anyone feels like helping, we wouldn't say no.
219
220 \S{faq-vb}{Question} Is the SSH or Telnet code available as a Visual
221 Basic component?
222
223 No, it isn't. None of the PuTTY team uses Visual Basic, and none of
224 us has any particular need to make SSH connections from a Visual
225 Basic application. In addition, all the preliminary work to turn it
226 into a DLL would be necessary first; and furthermore, we don't even
227 know how to write VB components.
228
229 If someone offers to do some of this work for us, we might consider
230 it, but unless that happens I can't see VB integration being
231 anywhere other than the very bottom of our priority list.
232
233 \S{faq-ipc}{Question} How can I use PuTTY to make an SSH connection
234 from within another program?
235
236 Probably your best bet is to use Plink, the command-line connection
237 tool. If you can start Plink as a second Windows process, and
238 arrange for your primary process to be able to send data to the
239 Plink process, and receive data from it, through pipes, then you
240 should be able to make SSH connections from your program.
241
242 This is what CVS for Windows does, for example.
243
244 \H{faq-details} Details of PuTTY's operation
245
246 \S{faq-term}{Question} What terminal type does PuTTY use?
247
248 For most purposes, PuTTY can be considered to be an \cw{xterm}
249 terminal, although full support for some of \cw{xterm}'s features,
250 such as passing mouse actions to the server-side program, is not
251 present in the 0.51 release (but has been added since).
252
253 PuTTY also supports some terminal control sequences not supported by
254 the real \cw{xterm}: notably the Linux console sequences that
255 reconfigure the colour palette, and the title bar control sequences
256 used by \cw{DECterm} (which are different from the \cw{xterm} ones;
257 PuTTY supports both).
258
259 By default, PuTTY announces its terminal type to the server as
260 \c{xterm}. If you have a problem with this, you can reconfigure it
261 to say something else; \c{vt220} might help if you have trouble.
262
263 \S{faq-settings}{Question} Where does PuTTY store its data?
264
265 PuTTY stores most of its data (saved sessions, SSH host keys) in the
266 Registry. The precise location is
267
268 \c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY
269
270 and within that area, saved sessions are stored under \c{Sessions}
271 while host keys are stored under \c{SshHostKeys}.
272
273 PuTTY also requires a random number seed file, to improve the
274 unpredictability of randomly chosen data needed as part of the SSH
275 cryptography. This is stored by default in your Windows home
276 directory (\c{%HOMEDRIVE%\\%HOMEPATH%}), or in the actual Windows
277 directory (such as \c{C:\\WINDOWS}) if the home directory doesn't
278 exist, for example if you're using Win95. If you want to change the
279 location of the random number seed file, you can put your chosen
280 pathname in the Registry, at
281
282 \c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\RandSeedFile
283
284 \H{faq-howto} HOWTO questions
285
286 \S{faq-startmax}{Question} How can I make PuTTY start up maximised?
287
288 Create a Windows shortcut to start PuTTY from, and set it as \q{Run
289 Maximized}.
290
291 \S{faq-startsess}{Question} How can I create a Windows shortcut to
292 start a particular saved session directly?
293
294 To run a PuTTY session saved under the name \q{\cw{mysession}},
295 create a Windows shortcut that invokes PuTTY with a command line
296 like
297
298 \c \path\name\to\putty.exe @mysession
299
300 \S{faq-startssh}{Question} How can I start an SSH session straight
301 from the command line?
302
303 Use the command line \c{putty -ssh host.name}. Alternatively, create
304 a saved session that specifies the SSH protocol, and start the saved
305 session as shown in \k{faq-startsess}.
306
307 \S{faq-cutpaste}{Question} How do I copy and paste between PuTTY and
308 other Windows applications?
309
310 Copy and paste works similarly to the X Window System. You use the
311 left mouse button to select text in the PuTTY window. The act of
312 selection \e{automatically} copies the text to the clipboard: there
313 is no need to press Ctrl-Ins or Ctrl-C or anything else. In fact,
314 pressing Ctrl-C will send a Ctrl-C character to the other end of
315 your connection (just like it does the rest of the time), which may
316 have unpleasant effects. The \e{only} thing you need to do, to copy
317 text to the clipboard, is to select it.
318
319 To paste the clipboard contents into a PuTTY window, by default you
320 click the right mouse button. If you have a three-button mouse and
321 are used to X applications, you can configure pasting to be done by
322 the middle button instead, but this is not the default because most
323 Windows users don't have a middle button at all.
324
325 You can also paste by pressing Shift-Ins.
326
327 \S{faq-tunnels}{Question} How do I use X forwarding and port
328 forwarding? I can't find the Tunnels panel.
329
330 If you're looking in the 0.51 release or earlier, the Tunnels panel
331 isn't there. It was added in the development snapshots after 0.51,
332 and releases 0.52 and onwards will contain it.
333
334 \S{faq-options}{Question} How do I use all PuTTY's features (public
335 keys, port forwarding, SSH v2, etc.) in PSCP, PSFTP and Plink?
336
337 The command-line tools are currently rather short of command line
338 options to enable this sort of thing. However, you can use most of
339 PuTTY's features if you create a PuTTY saved session, and then use
340 the name of the saved session on the command line in place of a
341 hostname. This works for PSCP, PSFTP and Plink (but don't expect
342 port forwarding in the file transfer applications!).
343
344 \S{faq-pscp}{Question} How do I use PSCP.EXE? When I double-click it
345 gives me a command prompt window which then closes instantly.
346
347 PSCP is a command-line application, not a GUI application. If you
348 run it without arguments, it will simply print a help message and
349 terminate.
350
351 To use PSCP properly, run it from a Command Prompt window. See
352 \k{pscp} in the documentation for more details.
353
354 \S{faq-pscp-spaces}{Question} How do I use PSCP to copy a file whose
355 name has spaces in?
356
357 If PSCP is using the traditional SCP protocol, this is confusing. If
358 you're specifying a file at the local end, you just use one set of
359 quotes as you would normally do:
360
361 \c pscp "local filename with spaces" user@host:
362 \c pscp user@host:myfile "local filename with spaces"
363
364 But if the filename you're specifying is on the \e{remote} side, you
365 have to use backslashes and two sets of quotes:
366
367 \c pscp user@host:"\"remote filename with spaces\"" local_filename
368 \c pscp local_filename user@host:"\"remote filename with spaces\""
369
370 Worse still, in a remote-to-local copy you have to specify the local
371 file name explicitly, otherwise PSCP will complain that they don't
372 match (unless you specified the \c{-unsafe} option). The following
373 command will give an error message:
374
375 \c c:\>pscp user@host:"\"oo er\"" .
376 \c warning: remote host tried to write to a file called 'oo er'
377 \c when we requested a file called '"oo er"'.
378
379 Instead, you need to specify the local file name in full:
380
381 \c c:\>pscp user@host:"\"oo er\"" "oo er"
382
383 If PSCP is using the newer SFTP protocol, none of this is a problem,
384 and all filenames with spaces in are specified using a single pair
385 of quotes in the obvious way:
386
387 \c pscp "local file" user@host:
388 \c pscp user@host:"remote file" .
389
390 \H{faq-trouble} Troubleshooting
391
392 \S{faq-incorrect-mac}{Question} Why do I see \q{Incorrect MAC
393 received on packet}?
394
395 This is due to a bug in old SSH 2 servers distributed by
396 \cw{ssh.com}. Version 2.3.0 and below of their SSH 2 server
397 constructs Message Authentication Codes in the wrong way, and
398 expects the client to construct them in the same wrong way. PuTTY
399 constructs the MACs correctly by default, and hence these old
400 servers will fail to work with it.
401
402 If you are using PuTTY version 0.51 or below, go to the SSH panel
403 and check the box labelled \q{Imitate SSH 2 MAC bug}. This will
404 cause PuTTY to construct its MACs in the same incorrect manner as
405 the buggy servers, so it will be able to work with them.
406
407 Since version 0.51, PuTTY has been enhanced to detect buggy servers
408 automatically (when they announce their version) and enable the
409 workaround without the user needing to ask. Therefore you \e{should}
410 never have to use this option again after 0.52, but it is still
411 provided just in case another buggy server shows up.
412
413 In this context MAC stands for Message Authentication Code. It's a
414 cryptographic term, and it has nothing at all to do with Ethernet
415 MAC (Media Access Control) addresses.
416
417 \S{faq-colours}{Question} I clicked on a colour in the Colours
418 panel, and the colour didn't change in my terminal.
419
420 That isn't how you're supposed to use the Colours panel.
421
422 During the course of a session, PuTTY potentially uses \e{all} the
423 colours listed in the Colours panel. It's not a question of using
424 only one of them and you choosing which one; PuTTY will use them
425 \e{all}. The purpose of the Colours panel is to let you adjust the
426 appearance of all the colours. So to change the colour of the
427 cursor, for example, you would select \q{Cursor Colour}, press the
428 \q{Modify} button, and select a new colour from the dialog box that
429 appeared. Similarly, if you want your session to appear in green,
430 you should select \q{Default Foreground} and press \q{Modify}.
431 Clicking on \q{ANSI Green} won't turn your session green; it will
432 only allow you to adjust the \e{shade} of green used when PuTTY is
433 instructed by the server to display green text.
434
435 \S{faq-winsock2}{Question} Plink on Windows 95 says it can't find
436 \cw{WS2_32.DLL}.
437
438 Plink requires the extended Windows network library, WinSock version
439 2. This is installed as standard on Windows 98 and above, and on
440 Windows NT, and even on later versions of Windows 95; but early
441 Win95 installations don't have it.
442
443 In order to use Plink on these systems, you will need to download
444 the
445 \W{http://www.microsoft.com/windows95/downloads/contents/wuadmintools/s_wunetworkingtools/w95sockets2/}{WinSock 2 upgrade}:
446
447 \c http://www.microsoft.com/windows95/downloads/contents/wuadmintools/
448 \c s_wunetworkingtools/w95sockets2/
449
450 \S{faq-rekey}{Question} My PuTTY sessions close after an hour and
451 tell me \q{Server failed host key check}.
452
453 This is a bug in all versions of PuTTY up to and including 0.51. SSH
454 v2 servers from \cw{ssh.com} will require the key exchange to be
455 repeated one hour after the start of the connection, and PuTTY will
456 get this wrong.
457
458 The bug has been fixed since version 0.51, so upgrading to a later
459 version or snapshot should solve the problem.
460
461 \S{faq-outofmem}{Question} After trying to establish an SSH 2
462 connection, PuTTY says \q{Out of memory} and dies.
463
464 If this happens just while the connection is starting up, this often
465 indicates that for some reason the client and server have failed to
466 establish a session encryption key. Somehow, they have performed
467 calculations that should have given each of them the same key, but
468 have ended up with different keys; so data encrypted by one and
469 decrypted by the other looks like random garbage.
470
471 This causes an \q{out of memory} error because the first encrypted
472 data PuTTY expects to see is the length of an SSH message. Normally
473 this will be something well under 100 bytes. If the decryption has
474 failed, PuTTY will see a completely random length in the region of
475 two \e{gigabytes}, and will try to allocate enough memory to store
476 this non-existent message. This will immediately lead to it thinking
477 it doesn't have enough memory, and panicking.
478
479 If this happens to you, it is quite likely to still be a PuTTY bug
480 and you should report it (although it might be a bug in your SSH
481 server instead); but it doesn't necessarily mean you've actually run
482 out of memory.
483
484 \S{faq-bce}{Question} When I run full-colour applications, I see
485 areas of black space where colour ought to be.
486
487 You almost certainly need to enable the \q{Use background colour to
488 erase screen} setting in the Terminal panel. Note that if you do
489 this in mid-session, it won't take effect until you reset the
490 terminal (see \k{faq-resetterm}).
491
492 \S{faq-resetterm}{Question} When I change some terminal settings,
493 nothing happens.
494
495 Some of the terminal options (notably Auto Wrap and
496 background-colour screen erase) actually represent the \e{default}
497 setting, rather than the currently active setting. The server can
498 send sequences that modify these options in mid-session, but when
499 the terminal is reset (by server action, or by you choosing \q{Reset
500 Terminal} from the System menu) the defaults are restored.
501
502 If you want to change one of these options in the middle of a
503 session, you will find that the change does not immediately take
504 effect. It will only take effect once you reset the terminal.
505
506 \S{faq-altgr}{Question} I can't type characters that require the
507 AltGr key.
508
509 In PuTTY version 0.51, the AltGr key was broken. The bug has been
510 fixed since then.
511
512 \S{faq-idleout}{Question} My PuTTY sessions unexpectedly close after
513 they are idle for a while.
514
515 Some types of firewall, and almost any router doing Network Address
516 Translation (NAT, also known as IP masquerading), will forget about
517 a connection through them if the connection does nothing for too
518 long. This will cause the connection to be rudely cut off when
519 contact is resumed.
520
521 You can try to combat this by telling PuTTY to send \e{keepalives}:
522 packets of data which have no effect on the actual session, but
523 which reassure the router or firewall that the network connection is
524 still active and worth remembering about.
525
526 Keepalives don't solve everything, unfortunately; although they
527 cause greater robustness against this sort of router, they can also
528 cause a \e{loss} of robustness against network dropouts. See
529 \k{config-keepalive} in the documentation for more discussion of
530 this.
531
532 \S{faq-timeout}{Question} PuTTY's network connections time out too
533 quickly when network connectivity is temporarily lost.
534
535 This is a Windows problem, not a PuTTY problem. The timeout value
536 can't be set on per application or per session basis. To increase
537 the TCP timeout globally, you need to tinker with the Registry.
538
539 On Windows 95, 98 or ME, the registry key you need to change is
540
541 \c HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\
542 \c MSTCP\MaxDataRetries
543
544 (it must be of type DWORD in Win95, or String in Win98/ME).
545
546 On Windows NT or 2000, the registry key is
547
548 \c HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\
549 \c Parameters\TcpMaxDataRetransmissions
550
551 and it must be of type DWORD.
552
553 Set the key's value to something like 10. This will cause Windows to
554 try harder to keep connections alive instead of abandoning them.
555
556 \S{faq-puttyputty}{Question} When I \cw{cat} a binary file, I get
557 `PuTTYPuTTYPuTTY' on my command line.
558
559 Don't do that, then.
560
561 This is designed behaviour; when PuTTY receives the character
562 Control-E from the remote server, it interprets it as a request to
563 identify itself, and so it sends back the string \q{\cw{PuTTY}} as
564 if that string had been entered at the keyboard. Control-E should
565 only be sent by programs that are prepared to deal with the
566 response. Writing a binary file to your terminal is likely to output
567 many Control-E characters, and cause this behaviour. Don't do it.
568 It's a bad plan.
569
570 To mitigate the effects, you could configure the answerback string
571 to be empty (see \k{config-answerback}); but writing binary files to
572 your terminal is likely to cause various other unpleasant behaviour,
573 so this is only a small remedy.
574
575 \S{faq-wintitle}{Question} When I \cw{cat} a binary file, my window
576 title changes to a nonsense string.
577
578 Don't do that, then.
579
580 It is designed behaviour that PuTTY should have the ability to
581 adjust the window title on instructions from the server. Normally
582 the control sequence that does this should only be sent
583 deliberately, by programs that know what they are doing and intend
584 to put meaningful text in the window title. Writing a binary file to
585 your terminal runs the risk of sending the same control sequence by
586 accident, and cause unexpected changes in the window title. Don't do
587 it.
588
589 \S{faq-password-fails}{Question} My keyboard stops working once
590 PuTTY displays the password prompt.
591
592 No, it doesn't. PuTTY just doesn't display the password you type, so
593 that someone looking at your screen can't see what it is.
594
595 Unlike the Windows login prompts, PuTTY doesn't display the password
596 as a row of asterisks either. This is so that someone looking at
597 your screen can't even tell how \e{long} your password is, which
598 might be valuable information.
599
600 \H{faq-secure} Security questions
601
602 \S{faq-publicpc}{Question} Is it safe for me to download PuTTY and
603 use it on a public PC?
604
605 It depends on whether you trust that PC. If you don't trust the
606 public PC, don't use PuTTY on it, and don't use any other software
607 you plan to type passwords into either. It might be watching your
608 keystrokes, or it might tamper with the PuTTY binary you download.
609 There is \e{no} program safe enough that you can run it on an
610 actively malicious PC and get away with typing passwords into it.
611
612 If you do trust the PC, then it's probably OK to use PuTTY on it
613 (but if you don't trust the network, then the PuTTY download might
614 be tampered with, so it would be better to carry PuTTY with you on a
615 floppy).
616
617 \S{faq-cleanup}{Question} What does PuTTY leave on a system? How can
618 I clean up after it?
619
620 PuTTY will leave some Registry entries, and a random seed file, on
621 the PC (see \k{faq-settings}). If you are using PuTTY on a public
622 PC, or somebody else's PC, you might want to clean these up when you
623 leave. You can do that automatically, by running the command
624 \c{putty -cleanup}.
625
626 \S{faq-dsa}{Question} How come PuTTY now supports DSA, when the
627 website used to say how insecure it was?
628
629 DSA has a major weakness \e{if badly implemented}: it relies on a
630 random number generator to far too great an extent. If the random
631 number generator produces a number an attacker can predict, the DSA
632 private key is exposed - meaning that the attacker can log in as you
633 on all systems that accept that key.
634
635 The PuTTY policy changed because the developers were informed of
636 ways to implement DSA which do not suffer nearly as badly from this
637 weakness, and indeed which don't need to rely on random numbers at
638 all. For this reason we now believe PuTTY's DSA implementation is
639 probably OK. However, if you have the choice, we still recommend you
640 use RSA instead.
641
642 \H{faq-admin} Administrative questions
643
644 \S{faq-domain}{Question} Would you like me to register you a nicer
645 domain name?
646
647 No, thank you. Even if you can find one (most of them seem to have
648 been registered already, by people who didn't ask whether we
649 actually wanted it before they applied), we're happy with the PuTTY
650 web site being exactly where it is. It's not hard to find (just type
651 \q{putty} into \W{http://www.google.com/}{google.com} and we're the
652 first link returned), and we don't believe the administrative hassle
653 of moving the site would be worth the benefit.
654
655 In addition, if we \e{did} want a custom domain name, we would want
656 to run it ourselves, so we knew for certain that it would continue
657 to point where we wanted it, and wouldn't suddenly change or do
658 strange things. Having it registered for us by a third party who we
659 don't even know is not the best way to achieve this.
660
661 \S{faq-webhosting}{Question} Would you like free web hosting for the
662 PuTTY web site?
663
664 We already have some, thanks.
665
666 \S{faq-sourceforge}{Question} Why don't you move PuTTY to
667 SourceForge?
668
669 Partly, because we don't want to move the web site location (see
670 \k{faq-domain}).
671
672 Also, security reasons. PuTTY is a security product, and as such it
673 is particularly important to guard the code and the web site against
674 unauthorised modifications which might introduce subtle security
675 flaws. Therefore, we prefer that the CVS repository, web site and
676 FTP site remain where they are, under the direct control of system
677 administrators we know and trust personally, rather than being run
678 by a large organisation full of people we've never met and which is
679 known to have had breakins in the past.
680
681 No offence to SourceForge; I think they do a wonderful job. But
682 they're not ideal for everyone, and in particular they're not ideal
683 for us.
684
685 \S{faq-mailinglist1}{Question} Why can't I subscribe to the
686 putty-bugs mailing list?
687
688 Because you're not a member of the PuTTY core development team. The
689 putty-bugs mailing list is not a general newsgroup-like discussion
690 forum; it's a contact address for the core developers, and an
691 \e{internal} mailing list for us to discuss things among ourselves.
692 If we opened it up for everybody to subscribe to, it would turn into
693 something more like a newsgroup and we would be completely
694 overwhelmed by the volume of traffic. It's hard enough to keep up
695 with the list as it is.
696
697 \S{faq-mailinglist2}{Question} If putty-bugs isn't a
698 general-subscription mailing list, what is?
699
700 There isn't one, that we know of.
701
702 If someone else wants to set up a mailing list for PuTTY users to
703 help each other with common problems, that would be fine with us;
704 but the PuTTY team would almost certainly not have the time to read
705 it, so any questions the list couldn't answer would have to be
706 forwarded on to us by the questioner. In any case, it's probably
707 better to use the established newsgroup \cw{comp.security.ssh} for
708 this purpose.
709
710 \S{faq-donations}{Question} How can I donate to PuTTY development?
711
712 Please, \e{please} don't feel you have to. PuTTY is completely free
713 software, and not shareware. We think it's very important that
714 \e{everybody} who wants to use PuTTY should be able to, whether they
715 have any money or not; so the last thing we would want is for a
716 PuTTY user to feel guilty because they haven't paid us any money. If
717 you want to keep your money, please do keep it. We wouldn't dream of
718 asking for any.
719
720 Having said all that, if you still really \e{want} to give us money,
721 we won't argue :-) The easiest way for us to accept donations is if
722 you go to \W{http://www.e-gold.com}\cw{www.e-gold.com}, and deposit
723 your donation in account number 174769. Then send us e-mail to let
724 us know you've done so (otherwise we might not notice for months!).
725
726 Small donations (tens of dollars or tens of euros) will probably be
727 spent on beer or curry, which helps motivate our volunteer team to
728 continue doing this for the world. Larger donations will be spent on
729 something that actually helps development, if we can find anything
730 (perhaps new hardware, or a copy of Windows 2000), but if we can't
731 find anything then we'll just distribute the money among the
732 developers. If you want to be sure your donation is going towards
733 something worthwhile, ask us first. If you don't like these terms,
734 feel perfectly free not to donate. We don't mind.
735
736 \S{faq-pronounce}{Question} How do I pronounce PuTTY?
737
738 Exactly like the normal word \q{putty}. Just like the stuff you put
739 on window frames. (One of the reasons it's called PuTTY is because
740 it makes Windows usable. :-)