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1 | \input texinfo @c -*-texinfo-*- |
2 | ||
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4 | |
5 | @set VERSION 0.1 | |
6 | ||
7 | ||
8 | @copying | |
9 | This file describes PGG, an Emacs interface to various PGP implementations. | |
10 | ||
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11 | Copyright @copyright{} 2001, 2003, 2004, 2005, 2006, 2007, 2008 |
12 | Free Software Foundation, Inc. | |
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13 | |
14 | @quotation | |
15 | Permission is granted to copy, distribute and/or modify this document | |
16 | under the terms of the GNU Free Documentation License, Version 1.2 or | |
17 | any later version published by the Free Software Foundation; with no | |
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18 | Invariant Sections, with the Front-Cover texts being ``A GNU Manual,'' |
19 | and with the Back-Cover Texts as in (a) below. A copy of the license | |
20 | is included in the section entitled ``GNU Free Documentation License.'' | |
21 | ||
22 | (a) The FSF's Back-Cover Text is: ``You have the freedom to copy and | |
23 | modify this GNU manual. Buying copies from the FSF supports it in | |
24 | developing GNU and promoting software freedom.'' | |
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25 | @end quotation |
26 | @end copying | |
27 | ||
28 | @dircategory Emacs | |
29 | @direntry | |
30 | * PGG: (pgg). Emacs interface to various PGP implementations. | |
31 | @end direntry | |
32 | ||
33 | @settitle PGG @value{VERSION} | |
34 | ||
35 | ||
36 | @titlepage | |
37 | @title PGG | |
38 | ||
39 | @author by Daiki Ueno | |
40 | @page | |
41 | ||
42 | @vskip 0pt plus 1filll | |
43 | @insertcopying | |
44 | @end titlepage | |
45 | @page | |
46 | ||
47 | @node Top | |
48 | @top PGG | |
49 | This manual describes PGG. PGG is an interface library between Emacs | |
50 | and various tools for secure communication. PGG also provides a simple | |
51 | user interface to encrypt, decrypt, sign, and verify MIME messages. | |
52 | ||
53 | @menu | |
54 | * Overview:: What PGG is. | |
55 | * Prerequisites:: Complicated stuff you may have to do. | |
56 | * How to use:: Getting started quickly. | |
57 | * Architecture:: | |
58 | * Parsing OpenPGP packets:: | |
59 | * GNU Free Documentation License:: The license for this documentation. | |
60 | * Function Index:: | |
61 | * Variable Index:: | |
62 | @end menu | |
63 | ||
64 | @node Overview | |
65 | @chapter Overview | |
66 | ||
67 | PGG is an interface library between Emacs and various tools for secure | |
68 | communication. Even though Mailcrypt has similar feature, it does not | |
69 | deal with detached PGP messages, normally used in PGP/MIME | |
70 | infrastructure. This was the main reason why I wrote the new library. | |
71 | ||
72 | PGP/MIME is an application of MIME Object Security Services (RFC1848). | |
73 | The standard is documented in RFC2015. | |
74 | ||
75 | @node Prerequisites | |
76 | @chapter Prerequisites | |
77 | ||
78 | PGG requires at least one implementation of privacy guard system. | |
79 | This document assumes that you have already obtained and installed them | |
80 | and that you are familiar with its basic functions. | |
81 | ||
82 | By default, PGG uses GnuPG. If you are new to such a system, I | |
83 | recommend that you should look over the GNU Privacy Handbook (GPH) | |
84 | which is available at @uref{http://www.gnupg.org/documentation/}. | |
85 | ||
86 | When using GnuPG, we recommend the use of the @code{gpg-agent} | |
87 | program, which is distributed with versions 2.0 and later of GnuPG. | |
88 | This is a daemon to manage private keys independently from any | |
89 | protocol, and provides the most secure way to input and cache your | |
90 | passphrases (@pxref{Caching passphrase}). By default, PGG will | |
91 | attempt to use @code{gpg-agent} if it is running. @xref{Invoking | |
92 | GPG-AGENT,,,gnupg,Using the GNU Privacy Guard}. | |
93 | ||
94 | PGG also supports Pretty Good Privacy version 2 or version 5. | |
95 | ||
96 | @node How to use | |
97 | @chapter How to use | |
98 | ||
99 | The toplevel interface of this library is quite simple, and only | |
100 | intended to use with public-key cryptographic operation. | |
101 | ||
102 | To use PGG, evaluate following expression at the beginning of your | |
103 | application program. | |
104 | ||
105 | @lisp | |
106 | (require 'pgg) | |
107 | @end lisp | |
108 | ||
109 | If you want to check existence of pgg.el at runtime, instead you can | |
110 | list autoload setting for desired functions as follows. | |
111 | ||
112 | @lisp | |
113 | (autoload 'pgg-encrypt-region "pgg" | |
114 | "Encrypt the current region." t) | |
115 | (autoload 'pgg-encrypt-symmetric-region "pgg" | |
116 | "Encrypt the current region with symmetric algorithm." t) | |
117 | (autoload 'pgg-decrypt-region "pgg" | |
118 | "Decrypt the current region." t) | |
119 | (autoload 'pgg-sign-region "pgg" | |
120 | "Sign the current region." t) | |
121 | (autoload 'pgg-verify-region "pgg" | |
122 | "Verify the current region." t) | |
123 | (autoload 'pgg-insert-key "pgg" | |
124 | "Insert the ASCII armored public key." t) | |
125 | (autoload 'pgg-snarf-keys-region "pgg" | |
126 | "Import public keys in the current region." t) | |
127 | @end lisp | |
128 | ||
129 | @menu | |
130 | * User Commands:: | |
131 | * Selecting an implementation:: | |
132 | * Caching passphrase:: | |
133 | * Default user identity:: | |
134 | @end menu | |
135 | ||
136 | @node User Commands | |
137 | @section User Commands | |
138 | ||
139 | At this time you can use some cryptographic commands. The behavior of | |
140 | these commands relies on a fashion of invocation because they are also | |
141 | intended to be used as library functions. In case you don't have the | |
142 | signer's public key, for example, the function @code{pgg-verify-region} | |
143 | fails immediately, but if the function had been called interactively, it | |
144 | would ask you to retrieve the signer's public key from the server. | |
145 | ||
146 | @deffn Command pgg-encrypt-region start end recipients &optional sign passphrase | |
147 | Encrypt the current region between @var{start} and @var{end} for | |
148 | @var{recipients}. When the function were called interactively, you | |
149 | would be asked about the recipients. | |
150 | ||
151 | If encryption is successful, it replaces the current region contents (in | |
152 | the accessible portion) with the resulting data. | |
153 | ||
154 | If optional argument @var{sign} is non-@code{nil}, the function is | |
155 | request to do a combined sign and encrypt. This currently is | |
156 | confirmed to work with GnuPG, but might not work with PGP or PGP5. | |
157 | ||
158 | If optional @var{passphrase} is @code{nil}, the passphrase will be | |
159 | obtained from the passphrase cache or user. | |
160 | @end deffn | |
161 | ||
162 | @deffn Command pgg-encrypt-symmetric-region &optional start end passphrase | |
163 | Encrypt the current region between @var{start} and @var{end} using a | |
164 | symmetric cipher. After invocation you are asked for a passphrase. | |
165 | ||
166 | If optional @var{passphrase} is @code{nil}, the passphrase will be | |
167 | obtained from the passphrase cache or user. | |
168 | ||
169 | symmetric-cipher encryption is currently only implemented for GnuPG. | |
170 | @end deffn | |
171 | ||
172 | @deffn Command pgg-decrypt-region start end &optional passphrase | |
173 | Decrypt the current region between @var{start} and @var{end}. If | |
174 | decryption is successful, it replaces the current region contents (in | |
175 | the accessible portion) with the resulting data. | |
176 | ||
177 | If optional @var{passphrase} is @code{nil}, the passphrase will be | |
178 | obtained from the passphrase cache or user. | |
179 | @end deffn | |
180 | ||
181 | @deffn Command pgg-sign-region start end &optional cleartext passphrase | |
182 | Make the signature from text between @var{start} and @var{end}. If the | |
183 | optional third argument @var{cleartext} is non-@code{nil}, or the | |
184 | function is called interactively, it does not create a detached | |
185 | signature. In such a case, it replaces the current region contents (in | |
186 | the accessible portion) with the resulting data. | |
187 | ||
188 | If optional @var{passphrase} is @code{nil}, the passphrase will be | |
189 | obtained from the passphrase cache or user. | |
190 | @end deffn | |
191 | ||
192 | @deffn Command pgg-verify-region start end &optional signature fetch | |
193 | Verify the current region between @var{start} and @var{end}. If the | |
194 | optional third argument @var{signature} is non-@code{nil}, it is treated | |
195 | as the detached signature file of the current region. | |
196 | ||
197 | If the optional 4th argument @var{fetch} is non-@code{nil}, or the | |
198 | function is called interactively, we attempt to fetch the signer's | |
199 | public key from the key server. | |
200 | @end deffn | |
201 | ||
202 | @deffn Command pgg-insert-key | |
203 | Retrieve the user's public key and insert it as ASCII-armored format. | |
204 | @end deffn | |
205 | ||
206 | @deffn Command pgg-snarf-keys-region start end | |
207 | Collect public keys in the current region between @var{start} and | |
208 | @var{end}, and add them into the user's keyring. | |
209 | @end deffn | |
210 | ||
211 | @node Selecting an implementation | |
212 | @section Selecting an implementation | |
213 | ||
214 | Since PGP has a long history and there are a number of PGP | |
215 | implementations available today, the function which each one has differs | |
216 | considerably. For example, if you are using GnuPG, you know you can | |
217 | select cipher algorithm from 3DES, CAST5, BLOWFISH, and so on, but on | |
218 | the other hand the version 2 of PGP only supports IDEA. | |
219 | ||
220 | Which implementation is used is controlled by the @code{pgg-scheme} | |
221 | variable. If it is @code{nil} (the default), the value of the | |
222 | @code{pgg-default-scheme} variable will be used instead. | |
223 | ||
224 | @defvar pgg-scheme | |
225 | Force specify the scheme of PGP implementation. The value can be set to | |
226 | @code{gpg}, @code{pgp}, and @code{pgp5}. The default is @code{nil}. | |
227 | @end defvar | |
228 | ||
229 | @defvar pgg-default-scheme | |
230 | The default scheme of PGP implementation. The value should be one of | |
231 | @code{gpg}, @code{pgp}, and @code{pgp5}. The default is @code{gpg}. | |
232 | @end defvar | |
233 | ||
234 | @node Caching passphrase | |
235 | @section Caching passphrase | |
236 | ||
237 | When using GnuPG (gpg) as the PGP scheme, we recommend using a program | |
238 | called @code{gpg-agent} for entering and caching | |
239 | passphrases@footnote{Actually, @code{gpg-agent} does not cache | |
240 | passphrases but private keys. On the other hand, from a user's point | |
241 | of view, this technical difference isn't visible.}. | |
242 | ||
243 | @defvar pgg-gpg-use-agent | |
244 | If non-@code{nil}, attempt to use @code{gpg-agent} whenever possible. | |
245 | The default is @code{t}. If @code{gpg-agent} is not running, or GnuPG | |
246 | is not the current PGP scheme, PGG's own passphrase-caching mechanism | |
247 | is used (see below). | |
248 | @end defvar | |
249 | ||
250 | To use @code{gpg-agent} with PGG, you must first ensure that | |
251 | @code{gpg-agent} is running. For example, if you are running in the X | |
252 | Window System, you can do this by putting the following line in your | |
253 | @file{.xsession} file: | |
254 | ||
255 | @smallexample | |
256 | eval "$(gpg-agent --daemon)" | |
257 | @end smallexample | |
258 | ||
259 | For more details on invoking @code{gpg-agent}, @xref{Invoking | |
260 | GPG-AGENT,,,gnupg,Using the GNU Privacy Guard}. | |
261 | ||
262 | Whenever you perform a PGG operation that requires a GnuPG passphrase, | |
263 | GnuPG will contact @code{gpg-agent}, which prompts you for the | |
264 | passphrase. Furthermore, @code{gpg-agent} ``caches'' the result, so | |
265 | that subsequent uses will not require you to enter the passphrase | |
266 | again. (This cache usually expires after a certain time has passed; | |
267 | you can change this using the @code{--default-cache-ttl} option when | |
268 | invoking @code{gpg-agent}.) | |
269 | ||
270 | If you are running in a X Window System environment, @code{gpg-agent} | |
271 | prompts for a passphrase by opening a graphical window. However, if | |
272 | you are running Emacs on a text terminal, @code{gpg-agent} has trouble | |
273 | receiving input from the terminal, since it is being sent to Emacs. | |
274 | One workaround for this problem is to run @code{gpg-agent} on a | |
275 | different terminal from Emacs, with the @code{--keep-tty} option; this | |
276 | tells @code{gpg-agent} use its own terminal to prompt for passphrases. | |
277 | ||
278 | When @code{gpg-agent} is not being used, PGG prompts for a passphrase | |
279 | through Emacs. It also has its own passphrase caching mechanism, | |
280 | which is controlled by the variable @code{pgg-cache-passphrase} (see | |
281 | below). | |
282 | ||
283 | There is a security risk in handling passphrases through PGG rather | |
284 | than @code{gpg-agent}. When you enter your passphrase into an Emacs | |
285 | prompt, it is temporarily stored as a cleartext string in the memory | |
286 | of the Emacs executable. If the executable memory is swapped to disk, | |
287 | the root user can, in theory, extract the passphrase from the | |
288 | swapfile. Furthermore, the swapfile containing the cleartext | |
289 | passphrase might remain on the disk after the system is discarded or | |
290 | stolen. @code{gpg-agent} avoids this problem by using certain tricks, | |
291 | such as memory locking, which have not been implemented in Emacs. | |
292 | ||
293 | @defvar pgg-cache-passphrase | |
294 | If non-@code{nil}, store passphrases. The default value of this | |
295 | variable is @code{t}. If you are worried about security issues, | |
296 | however, you could stop the caching of passphrases by setting this | |
297 | variable to @code{nil}. | |
298 | @end defvar | |
299 | ||
300 | @defvar pgg-passphrase-cache-expiry | |
301 | Elapsed time for expiration in seconds. | |
302 | @end defvar | |
303 | ||
304 | If your passphrase contains non-ASCII characters, you might need to | |
305 | specify the coding system to be used to encode your passphrases, since | |
306 | GnuPG treats them as a byte sequence, not as a character sequence. | |
307 | ||
308 | @defvar pgg-passphrase-coding-system | |
309 | Coding system used to encode passphrase. | |
310 | @end defvar | |
311 | ||
312 | @node Default user identity | |
313 | @section Default user identity | |
314 | ||
315 | The PGP implementation is usually able to select the proper key to use | |
316 | for signing and decryption, but if you have more than one key, you may | |
317 | need to specify the key id to use. | |
318 | ||
319 | @defvar pgg-default-user-id | |
320 | User ID of your default identity. It defaults to the value returned | |
321 | by @samp{(user-login-name)}. You can customize this variable. | |
322 | @end defvar | |
323 | ||
324 | @defvar pgg-gpg-user-id | |
325 | User ID of the GnuPG default identity. It defaults to @samp{nil}. | |
326 | This overrides @samp{pgg-default-user-id}. You can customize this | |
327 | variable. | |
328 | @end defvar | |
329 | ||
330 | @defvar pgg-pgp-user-id | |
331 | User ID of the PGP 2.x/6.x default identity. It defaults to | |
332 | @samp{nil}. This overrides @samp{pgg-default-user-id}. You can | |
333 | customize this variable. | |
334 | @end defvar | |
335 | ||
336 | @defvar pgg-pgp5-user-id | |
337 | User ID of the PGP 5.x default identity. It defaults to @samp{nil}. | |
338 | This overrides @samp{pgg-default-user-id}. You can customize this | |
339 | variable. | |
340 | @end defvar | |
341 | ||
342 | @node Architecture | |
343 | @chapter Architecture | |
344 | ||
345 | PGG introduces the notion of a "scheme of PGP implementation" (used | |
346 | interchangeably with "scheme" in this document). This term refers to a | |
347 | singleton object wrapped with the luna object system. | |
348 | ||
349 | Since PGG was designed for accessing and developing PGP functionality, | |
350 | the architecture had to be designed not just for interoperability but | |
351 | also for extensiblity. In this chapter we explore the architecture | |
01c52d31 | 352 | while finding out how to write the PGG back end. |
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353 | |
354 | @menu | |
355 | * Initializing:: | |
01c52d31 | 356 | * Back end methods:: |
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357 | * Getting output:: |
358 | @end menu | |
359 | ||
360 | @node Initializing | |
361 | @section Initializing | |
362 | ||
363 | A scheme must be initialized before it is used. | |
364 | It had better guarantee to keep only one instance of a scheme. | |
365 | ||
366 | The following code is snipped out of @file{pgg-gpg.el}. Once an | |
367 | instance of @code{pgg-gpg} scheme is initialized, it's stored to the | |
368 | variable @code{pgg-scheme-gpg-instance} and will be reused from now on. | |
369 | ||
370 | @lisp | |
371 | (defvar pgg-scheme-gpg-instance nil) | |
372 | ||
373 | (defun pgg-make-scheme-gpg () | |
374 | (or pgg-scheme-gpg-instance | |
375 | (setq pgg-scheme-gpg-instance | |
376 | (luna-make-entity 'pgg-scheme-gpg)))) | |
377 | @end lisp | |
378 | ||
379 | The name of the function must follow the | |
01c52d31 | 380 | regulation---@code{pgg-make-scheme-} follows the back end name. |
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01c52d31 MB |
382 | @node Back end methods |
383 | @section Back end methods | |
4009494e | 384 | |
01c52d31 | 385 | In each back end, these methods must be present. The output of these |
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386 | methods is stored in special buffers (@ref{Getting output}), so that |
387 | these methods must tell the status of the execution. | |
388 | ||
389 | @deffn Method pgg-scheme-lookup-key scheme string &optional type | |
390 | Return keys associated with @var{string}. If the optional third | |
391 | argument @var{type} is non-@code{nil}, it searches from the secret | |
392 | keyrings. | |
393 | @end deffn | |
394 | ||
395 | @deffn Method pgg-scheme-encrypt-region scheme start end recipients &optional sign passphrase | |
396 | Encrypt the current region between @var{start} and @var{end} for | |
397 | @var{recipients}. If @var{sign} is non-@code{nil}, do a combined sign | |
398 | and encrypt. If encryption is successful, it returns @code{t}, | |
399 | otherwise @code{nil}. | |
400 | @end deffn | |
401 | ||
402 | @deffn Method pgg-scheme-encrypt-symmetric-region scheme start end &optional passphrase | |
403 | Encrypt the current region between @var{start} and @var{end} using a | |
404 | symmetric cipher and a passphrases. If encryption is successful, it | |
405 | returns @code{t}, otherwise @code{nil}. This function is currently only | |
406 | implemented for GnuPG. | |
407 | @end deffn | |
408 | ||
409 | @deffn Method pgg-scheme-decrypt-region scheme start end &optional passphrase | |
410 | Decrypt the current region between @var{start} and @var{end}. If | |
411 | decryption is successful, it returns @code{t}, otherwise @code{nil}. | |
412 | @end deffn | |
413 | ||
414 | @deffn Method pgg-scheme-sign-region scheme start end &optional cleartext passphrase | |
415 | Make the signature from text between @var{start} and @var{end}. If the | |
416 | optional third argument @var{cleartext} is non-@code{nil}, it does not | |
417 | create a detached signature. If signing is successful, it returns | |
418 | @code{t}, otherwise @code{nil}. | |
419 | @end deffn | |
420 | ||
421 | @deffn Method pgg-scheme-verify-region scheme start end &optional signature | |
422 | Verify the current region between @var{start} and @var{end}. If the | |
423 | optional third argument @var{signature} is non-@code{nil}, it is treated | |
424 | as the detached signature of the current region. If the signature is | |
425 | successfully verified, it returns @code{t}, otherwise @code{nil}. | |
426 | @end deffn | |
427 | ||
428 | @deffn Method pgg-scheme-insert-key scheme | |
429 | Retrieve the user's public key and insert it as ASCII-armored format. | |
430 | On success, it returns @code{t}, otherwise @code{nil}. | |
431 | @end deffn | |
432 | ||
433 | @deffn Method pgg-scheme-snarf-keys-region scheme start end | |
434 | Collect public keys in the current region between @var{start} and | |
435 | @var{end}, and add them into the user's keyring. | |
436 | On success, it returns @code{t}, otherwise @code{nil}. | |
437 | @end deffn | |
438 | ||
439 | @node Getting output | |
440 | @section Getting output | |
441 | ||
01c52d31 | 442 | The output of the back end methods (@ref{Back end methods}) is stored in |
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443 | special buffers, so that these methods must tell the status of the |
444 | execution. | |
445 | ||
446 | @defvar pgg-errors-buffer | |
447 | The standard error output of the execution of the PGP command is stored | |
448 | here. | |
449 | @end defvar | |
450 | ||
451 | @defvar pgg-output-buffer | |
452 | The standard output of the execution of the PGP command is stored here. | |
453 | @end defvar | |
454 | ||
455 | @defvar pgg-status-buffer | |
456 | The rest of status information of the execution of the PGP command is | |
457 | stored here. | |
458 | @end defvar | |
459 | ||
460 | @node Parsing OpenPGP packets | |
461 | @chapter Parsing OpenPGP packets | |
462 | ||
463 | The format of OpenPGP messages is maintained in order to publish all | |
464 | necessary information needed to develop interoperable applications. | |
465 | The standard is documented in RFC 2440. | |
466 | ||
467 | PGG has its own parser for the OpenPGP packets. | |
468 | ||
469 | @defun pgg-parse-armor string | |
470 | List the sequence of packets in @var{string}. | |
471 | @end defun | |
472 | ||
473 | @defun pgg-parse-armor-region start end | |
474 | List the sequence of packets in the current region between @var{start} | |
475 | and @var{end}. | |
476 | @end defun | |
477 | ||
478 | @defvar pgg-ignore-packet-checksum | |
479 | If non-@code{nil}, don't check the checksum of the packets. | |
480 | @end defvar | |
481 | ||
482 | @node GNU Free Documentation License | |
483 | @appendix GNU Free Documentation License | |
484 | @include doclicense.texi | |
485 | ||
486 | @node Function Index | |
487 | @unnumbered Function Index | |
488 | @printindex fn | |
489 | ||
490 | @node Variable Index | |
491 | @unnumbered Variable Index | |
492 | @printindex vr | |
493 | ||
494 | @summarycontents | |
495 | @contents | |
496 | @bye | |
497 | ||
498 | @c End: | |
499 | ||
500 | @ignore | |
501 | arch-tag: 0c205838-34b9-41a5-b9d7-49ae57ccac85 | |
502 | @end ignore |