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c65df279 | 1 | .\" -*-nroff-*- |
2 | .de VS | |
3 | .sp 1 | |
4 | .RS | |
5 | .nf | |
6 | .ft B | |
7 | .. | |
8 | .de VE | |
9 | .ft R | |
10 | .fi | |
11 | .RE | |
12 | .sp 1 | |
13 | .. | |
14 | .ie t \{\ | |
15 | . if \n(.g \{\ | |
16 | . fam P | |
17 | . \} | |
18 | .\} | |
19 | .de hP | |
20 | .IP | |
21 | .ft B | |
22 | \h'-\w'\\$1\ 'u'\\$1\ \c | |
23 | .ft P | |
24 | .. | |
25 | .ie t .ds o \(bu | |
26 | .el .ds o o | |
27 | .TH catcrypt 1 "30 September 2004" "Straylight/Edgeware" "Catacomb cryptographic library" | |
28 | .SH NAME | |
29 | catcrypt \- encrypt and decrypt messages | |
30 | .SH SYNOPSIS | |
31 | .B catcrypt | |
32 | .RB [ \-k | |
33 | .IR keyring ] | |
34 | .I command | |
35 | .PP | |
36 | where | |
37 | .I command | |
38 | is one of: | |
39 | .PP | |
40 | .B help | |
41 | .RI [ command ...] | |
42 | .br | |
43 | .B show | |
44 | .RI [ item ...] | |
45 | .br | |
46 | .B encrypt | |
cd6eca43 | 47 | .RB [ \-apC ] |
c65df279 | 48 | .RB [ \-k |
49 | .IR tag ] | |
50 | .RB [ \-f | |
51 | .IR format ] | |
52 | .RB [ \-o | |
53 | .IR output ] | |
54 | .RI [ file ] | |
55 | .br | |
56 | .B decrypt | |
cd6eca43 | 57 | .RB [ \-apqvC ] |
c65df279 | 58 | .RB [ \-f |
59 | .IR format ] | |
60 | .RB [ \-o | |
61 | .IR output ] | |
62 | .RI [ file ] | |
63 | .br | |
64 | .B encode | |
cd6eca43 | 65 | .RB [ \-p ] |
c65df279 | 66 | .RB [ \-f |
67 | .IR format ] | |
68 | .RB [ \-b | |
69 | .IR boundary ] | |
70 | .RB [ \-o | |
71 | .IR output ] | |
72 | .RI [ file ] | |
73 | .br | |
fa54fe1e | 74 | .B decode |
cd6eca43 | 75 | .RB [ \-p ] |
c65df279 | 76 | .RB [ \-f |
77 | .IR format ] | |
78 | .RB [ \-b | |
79 | .IR boundary ] | |
80 | .RB [ \-o | |
81 | .IR output ] | |
82 | .RI [ file ] | |
83 | .SH "DESCRIPTION" | |
84 | The | |
85 | .B catcrypt | |
86 | command encrypts and decrypts messages. It also works as a simple PEM | |
87 | encoder and decoder. It provides a number of subcommands, by which the | |
88 | various operations may be carried out. | |
89 | .SS "Global options" | |
90 | Before the command name, | |
91 | .I "global options" | |
92 | may be given. The following global options are supported: | |
93 | .TP | |
94 | .BR "\-h, \-\-help " [ \fIcommand ...] | |
95 | Writes a brief summary of | |
96 | .BR catcrypt 's | |
97 | various options to standard output, and returns a successful exit | |
98 | status. With command names, gives help on those commands. | |
99 | .TP | |
100 | .B "\-v, \-\-version" | |
101 | Writes the program's version number to standard output, and returns a | |
102 | successful exit status. | |
103 | .TP | |
104 | .B "\-u, \-\-usage" | |
105 | Writes a very terse command line summary to standard output, and returns | |
106 | a successful exit status. | |
107 | .TP | |
108 | .BI "\-k, \-\-keyring " file | |
109 | Names the keyring file which | |
110 | .B key | |
111 | is to process. The default keyring, used if this option doesn't specify | |
112 | one, is the file named | |
113 | .B keyring | |
114 | in the current directory. See | |
115 | .BR key (1) | |
116 | and | |
117 | .BR keyring (5) | |
118 | for more details about keyring files. | |
119 | .SH "KEY SETUP" | |
120 | Algorithms to be used with a particular key are described by attributes | |
121 | on the key, or its type. The | |
122 | .B catcrypt | |
fa54fe1e | 123 | command deals with both signing and key-encapsulation keys. (Note that |
124 | .B catcrypt | |
45c0fd36 | 125 | uses signing keys in the same way as |
fa54fe1e | 126 | .BR catsign (1).) |
c65df279 | 127 | .SS "Key-encapsulation keys" |
128 | (Key encapsulation is a means of transmitting a short, known, random | |
129 | secret to a recipient. It differs from encryption in technical ways | |
130 | which are largely uninteresting at this point.) | |
131 | .PP | |
132 | A | |
133 | .I kemalgspec | |
134 | has the syntax | |
135 | .IR kem \c | |
136 | .RB [ / \c | |
137 | .IR cipher \c | |
138 | .RB [ / \c | |
139 | .IR hash ]]. | |
140 | If a | |
141 | .B kem | |
142 | attribute is present on the key, then it must have this form; otherwise, | |
143 | the key's type must have the form | |
144 | .BR cckem- \c | |
145 | .IR kemalgspec . | |
146 | Algorithm selections are taken from appropriately-named attributes, or, | |
147 | failing that, from the | |
148 | .IR kemalgspec . | |
149 | .PP | |
150 | The key-encapsulation mechanism is chosen according to the setting of | |
151 | .I kem | |
152 | as follows. Run | |
153 | .B catcrypt show kem | |
154 | for a list of supported KEMs. | |
155 | .TP | |
156 | .B rsa | |
157 | This is Shoup's RSA-KEM (formerly Simple RSA); see | |
158 | .I | |
159 | A proposal for an ISO standard for public key encryption (version 2.0) | |
160 | available at | |
161 | .BR http://eprint.iacr.org/2000/060/ . | |
162 | Use the | |
163 | .B rsa | |
164 | algorithm of the | |
165 | .B key add | |
166 | command (see | |
167 | .BR key (1)) | |
168 | to generate the key. | |
169 | .TP | |
170 | .B dh | |
171 | This is standard Diffie-Hellman key exchange, hashing the resulting | |
172 | shared secret to form the key, as used in, e.g., DLIES (P1363a). | |
173 | Use the | |
174 | .B dh | |
175 | algorithm of the | |
176 | .B key add | |
177 | command, preferably with the | |
178 | .B \-LS | |
179 | options, to generate the key. | |
180 | .TP | |
181 | .B ec | |
182 | This is the elliptic-curve analogue of | |
b98200ad | 183 | .BR dh . |
184 | Use the | |
c65df279 | 185 | .B ec |
186 | algorithm of the | |
187 | .BR key (1)) | |
188 | command to generate the key. | |
02dfbd5b MW |
189 | .TP |
190 | .B symm | |
191 | This is a simple symmetric encapsulation scheme. It works by hashing a | |
192 | binary key with a randomly-generated salt. Use the | |
193 | .B binary | |
194 | algorithm of the | |
195 | .B key add | |
196 | command (see | |
197 | .BR key (1)) | |
198 | to generate the key. | |
c65df279 | 199 | .PP |
200 | As well as the KEM itself, a number of supporting algorithms are used. | |
201 | These are taken from appropriately named attributes on the key or, | |
202 | failing that, derived from other attributes as described below. | |
203 | .TP | |
204 | .B cipher | |
205 | This is the symmetric encryption algorithm used for bulk data | |
206 | encryption. If there is no | |
207 | .B cipher | |
208 | attribute then the | |
209 | .I cipher | |
210 | in the | |
211 | .I kemalgspec | |
212 | is used; if that it absent, then the default of | |
213 | .B blowfish-cbc | |
214 | is used. Run | |
215 | .B catcrypt show cipher | |
216 | for a list of supported symmetric encryption algorithms. | |
217 | .TP | |
218 | .B hash | |
219 | This is the hash function used to distil entropy from the shared secret | |
220 | constructed by the raw KEM. If there is no | |
221 | .B hash | |
222 | attribute then the | |
223 | .I hash | |
224 | in the | |
b98200ad | 225 | .I kemalgspec |
226 | is used; if that is absent then the default of | |
c65df279 | 227 | .B rmd160 |
228 | is used. Run | |
229 | .B catcrypt show hash | |
230 | for a list of supported symmetric encryption algorithms. | |
231 | .TP | |
232 | .B mac | |
233 | This is the message authentication algorithm used during bulk data | |
234 | encryption to ensure integrity of the encrypted message and defend | |
235 | against chosen-ciphertext attacks. If there is no | |
236 | .B mac | |
237 | attribute then | |
238 | .IB hash -hmac | |
239 | is chosen as a default. Run | |
240 | .B catcrypt show mac | |
241 | for a list of supported message authentication algorithms. | |
242 | .TP | |
243 | .B kdf | |
244 | This is the key derivation function used to stretch the hashed shared | |
245 | secret to a sufficient length to select symmetric encryption and | |
246 | authentication keys, initialization vectors and other necessary | |
247 | pseudorandom quantities. If there is no | |
248 | .B kdf | |
249 | attribute then | |
250 | .IB hash -mgf | |
251 | is chosen as a default. Run | |
252 | .B catcrypt show kdf | |
253 | for a list of supported key derivation functions. | |
254 | .B Caution! | |
255 | Not all supported functions have the required security features: don't | |
256 | override the default choice unless you know what you're doing. | |
257 | .SS "Signing keys" | |
258 | A | |
259 | .I sigalgspec | |
260 | has the form | |
261 | .IR sig \c | |
262 | .RB [ / \c | |
263 | .IR hash ]. | |
264 | If a | |
265 | .B sig | |
266 | attribute is present on the key, then it must have this form; otherwise, | |
267 | the key's type must have the form | |
268 | .BI ccsig- \c | |
269 | .IR sigalgspec . | |
270 | Algorithm selections are taken from appropriately-named attributes, or, | |
271 | failing that, from the | |
272 | .IR sigalgspec . | |
273 | .PP | |
274 | The signature algorithm is chosen according to the setting of | |
275 | .I sig | |
276 | as follows. Run | |
277 | .B catcrypt show sig | |
278 | for a list of supported signature algorithms. | |
279 | .TP | |
280 | .B rsapkcs1 | |
281 | This is almost the same as the RSASSA-PKCS1-v1_5 algorithm described in | |
282 | RFC3447; the difference is that the hash is left bare rather than being | |
45c0fd36 | 283 | wrapped in a DER-encoded |
c65df279 | 284 | .B DigestInfo |
285 | structure. This doesn't affect security since the key can only be used | |
286 | with the one hash function anyway, and dropping the DER wrapping permits | |
287 | rapid adoption of new hash functions. Regardless, use of this algorithm | |
288 | is not recommended, since the padding method has been shown vulnerable | |
289 | to attack. Use the | |
290 | .B rsa | |
291 | algorithm of the | |
292 | .B key add | |
293 | command (see | |
294 | .BR key (1)) | |
295 | to generate the key. | |
296 | .TP | |
297 | .B rsapss | |
298 | This is the RSASSA-PSS algorithm described in RFC3447. It is the | |
299 | preferred RSA-based signature scheme. Use the | |
300 | .B rsa | |
301 | algorithm of the | |
302 | .B key add | |
303 | command (see | |
304 | .BR key (1)) | |
305 | to generate the key. | |
306 | .TP | |
307 | .B dsa | |
45c0fd36 | 308 | This is the DSA algorithm described in FIPS180-1 and FIPS180-2. Use the |
c65df279 | 309 | .B dsa |
310 | algorithm of the | |
311 | .B key add | |
312 | command (see | |
313 | .BR key (1)) | |
314 | to generate the key. | |
315 | .TP | |
316 | .B ecdsa | |
317 | This is the ECDSA algorithm described in ANSI X9.62 and FIPS180-2. Use | |
318 | the | |
319 | .B ec | |
320 | algorithm of the | |
321 | .B key add | |
322 | command (see | |
323 | .BR key (1)) | |
324 | to generate the key. | |
325 | .TP | |
326 | .B kcdsa | |
327 | This is the revised KCDSA (Korean Certificate-based Digital Signature | |
328 | Algorithm) described in | |
329 | .I The Revised Version of KCDSA | |
330 | .RB ( http://dasan.sejong.ac.kr/~chlim/pub/kcdsa1.ps ). | |
331 | Use the | |
332 | .B dh | |
333 | algorithm of the | |
334 | .B key add | |
335 | command with the | |
336 | .B \-LS | |
337 | options (see | |
338 | .BR key (1)) | |
339 | to generate the key. | |
340 | .TP | |
341 | .B eckcdsa | |
342 | This is an unofficial elliptic-curve analogue of the KCDSA algorithm. | |
343 | Use the | |
344 | .B ec | |
345 | algorithm of the | |
346 | .B key add | |
347 | command (see | |
348 | .BR key (1)) | |
349 | to generate the key. | |
02dfbd5b MW |
350 | .TP |
351 | .B mac | |
352 | This uses a symmetric message-authentication algorithm rather than a | |
353 | digital signature. The precise message-authentication scheme used is | |
354 | determined by the | |
355 | .B mac | |
356 | attribute on the key, which defaults to | |
357 | .IB hash -hmac | |
358 | if unspecified. Use the | |
359 | .B binary | |
360 | algorithm of the | |
361 | .B key add | |
362 | command (see | |
363 | .BR key (1)) | |
364 | to generate the key. | |
c65df279 | 365 | .PP |
366 | As well as the signature algorithm itself, a hash function is used. | |
367 | This is taken from the | |
368 | .B hash | |
369 | attribute on the key, or, failing that, from the | |
370 | .I hash | |
371 | specified in the | |
372 | .IR sigalgspec , | |
373 | or, if that is absent, determined by the signature algorithm as follows. | |
374 | .hP \*o | |
375 | For | |
376 | .BR rsapkcs1 , | |
377 | .BR rsapss , | |
378 | .BR dsa , | |
379 | and | |
380 | .BR ecdsa , | |
381 | the default hash function is | |
382 | .BR sha . | |
383 | .hP \*o | |
384 | For | |
45c0fd36 | 385 | .BR kcdsa |
c65df279 | 386 | and |
387 | .BR eckcdsa , | |
388 | the default hash function is | |
389 | .BR has160 . | |
390 | .PP | |
391 | Run | |
392 | .B catcrypt show hash | |
393 | for a list of supported hash functions. | |
394 | .SH "ENCODINGS" | |
395 | Two encodings for the ciphertext are supported. | |
396 | .TP | |
397 | .B binary | |
398 | The raw format, which has the benefit of being smaller, but needs to be | |
399 | attached to mail messages and generally handled with care. | |
400 | .TP | |
401 | .B pem | |
402 | PEM-encapsulated Base-64 encoded text. This format can be included | |
403 | directly in email and picked out again automatically; but there is a | |
404 | 4-to-3 data expansion as a result. | |
405 | .SH "COMMAND REFERENCE" | |
406 | .SS help | |
407 | The | |
408 | .B help | |
409 | command behaves exactly as the | |
410 | .B \-\-help | |
411 | option. With no arguments, it shows an overview of | |
412 | .BR catcrypt 's | |
413 | options; with arguments, it describes the named subcommands. | |
414 | .SS show | |
415 | The | |
416 | .B show | |
417 | command prints various lists of tokens understood by | |
418 | .BR catcrypt . | |
419 | With no arguments, it prints all of the lists; with arguments, it prints | |
420 | just the named lists, in order. The recognized lists can be enumerated | |
421 | using the | |
422 | .VS | |
423 | catcrypt show list | |
424 | .VE | |
425 | command. The lists are as follows. | |
426 | .TP | |
427 | .B list | |
428 | The lists which can be enumerated by the | |
429 | .B show | |
430 | command. | |
431 | .TP | |
432 | .B kem | |
433 | The key-encapsulation algorithms which can be used in a | |
434 | key-encapsulation key's | |
435 | .B kem | |
436 | attribute. | |
437 | .TP | |
438 | .B cipher | |
439 | The symmetric encryption algorithms which can be used in a | |
440 | key-encapsulation key's | |
441 | .B cipher | |
442 | attribute. | |
443 | .TP | |
444 | .B mac | |
445 | The message authentication algorithms which can be used in a | |
446 | key-encapsulation key's | |
447 | .B mac | |
448 | attribute. | |
449 | .TP | |
450 | .B sig | |
451 | The signature algorithms which can be used in a signing key's | |
452 | .B sig | |
453 | attribute. | |
454 | .TP | |
455 | .B hash | |
456 | The hash functions which can be used in a key's | |
457 | .B hash | |
458 | attribute. | |
459 | .TP | |
460 | .B enc | |
45c0fd36 | 461 | The encodings which can be applied to encrypted messages; see |
c65df279 | 462 | .B ENCODINGS |
463 | above. | |
464 | .SS encrypt | |
465 | The | |
466 | .B encrypt | |
467 | command encrypts a file and writes out the appropriately-encoded | |
468 | ciphertext. By default, it reads from standard input and writes to | |
469 | standard output. If a filename argument is given, this file is read | |
470 | instead (as binary data). | |
471 | .PP | |
472 | The following options are recognized. | |
473 | .TP | |
474 | .B "\-a, \-\-armour" | |
475 | Produce ASCII-armoured output. This is equivalent to specifying | |
476 | .BR "\-f pem" . | |
477 | The variant spelling | |
478 | .B "\-\-armor" | |
479 | is also accepted. | |
480 | .TP | |
481 | .BI "\-f, \-\-format " format | |
482 | Produce output encoded according to | |
483 | .IR format . | |
484 | .TP | |
485 | .BI "\-k, \-\-key " tag | |
486 | Use the key-encapsulation key named | |
487 | .I tag | |
488 | in the current keyring; the default key is | |
489 | .BR ccrypt . | |
490 | .TP | |
cd6eca43 MW |
491 | .BI "\-p, \-\-progress" |
492 | Write a progress meter to standard error while processing large files. | |
493 | .TP | |
c65df279 | 494 | .BI "\-s, \-\-sign-key " tag |
495 | Use the signature key named | |
496 | .I tag | |
497 | in the current keyring; the default is not to sign the ciphertext. | |
498 | .TP | |
499 | .BI "\-o, \-\-ouptut " file | |
500 | Write output to | |
501 | .I file | |
502 | rather than to standard output. | |
946c3f72 | 503 | .TP |
504 | .B "\-C, \-\-nocheck" | |
505 | Don't check the public key for validity. This makes encryption go much | |
506 | faster, but at the risk of using a duff key. | |
c65df279 | 507 | .SS decrypt |
508 | The | |
509 | .B decrypt | |
510 | command decrypts a ciphertext and writes out the plaintext. By default, | |
511 | it reads from standard input and writes to standard output. If a | |
512 | filename argument is given, this file is read instead. | |
513 | .PP | |
514 | The following options are recognized. | |
515 | .TP | |
516 | .B "\-a, \-\-armour" | |
fa54fe1e | 517 | Read ASCII-armoured input. This is equivalent to specifying |
c65df279 | 518 | .BR "\-f pem" . |
519 | The variant spelling | |
520 | .B "\-\-armor" | |
521 | is also accepted. | |
522 | .TP | |
fa54fe1e | 523 | .B "\-b, \-\-buffer" |
524 | Buffer plaintext data until we're sure we've got it all. This is forced | |
525 | on if output is to stdout, but is always available as an option. | |
526 | .TP | |
c65df279 | 527 | .BI "\-f, \-\-format " format |
528 | Read input encoded according to | |
529 | .IR format . | |
530 | .TP | |
cd6eca43 MW |
531 | .BI "\-p, \-\-progress" |
532 | Write a progress meter to standard error while processing large files. | |
533 | .TP | |
c65df279 | 534 | .B "\-v, \-\-verbose" |
535 | Produce more verbose messages. See below for the messages produced | |
536 | during decryption. The default verbosity level is 1. (Currently this | |
537 | is the most verbose setting. This might not be the case always.) | |
538 | .TP | |
539 | .B "\-q, \-\-quiet" | |
540 | Produce fewer messages. | |
541 | .TP | |
542 | .BI "\-o, \-\-output " file | |
543 | Write output to | |
544 | .I file | |
545 | instead of to standard output. The file is written in binary mode. | |
546 | Fixing line-end conventions is your problem; there are lots of good | |
547 | tools for dealing with it. | |
946c3f72 | 548 | .TP |
549 | .B "\-C, \-\-nocheck" | |
550 | Don't check the private key for validity. This makes decryption go much | |
551 | faster, but at the risk of using a duff key, and possibly leaking | |
552 | information about the private key. | |
c65df279 | 553 | .PP |
554 | Output is written to standard output in a machine-readable format. | |
555 | Major problems cause the program to write a diagnostic to standard error | |
556 | and exit nonzero as usual. The quantity of output varies depending on | |
557 | the verbosity level and whether the plaintext is also being written to | |
fa54fe1e | 558 | standard output. Output lines begin with a keyword: |
c65df279 | 559 | .TP |
560 | .BI "FAIL " reason | |
561 | An error prevented decryption. The program will exit nonzero. | |
562 | .TP | |
563 | .BI "WARN " reason | |
564 | .B catcrypt | |
565 | encountered a situation which may or may not invalidate the decryption. | |
45c0fd36 | 566 | .TP |
c65df279 | 567 | .BI "OK " message |
568 | Decryption was successful. This is only produced if main output is | |
569 | being sent somewhere other than standard output. | |
570 | .TP | |
571 | .B "DATA" | |
572 | The plaintext follows, starting just after the next newline character or | |
b98200ad | 573 | sequence. This is only produced if main output is also being sent to |
fa54fe1e | 574 | standard output. |
c65df279 | 575 | .TP |
576 | .BI "INFO " note | |
577 | Any other information. | |
578 | .PP | |
579 | The information written at the various verbosity levels is as follows. | |
580 | .hP 0. | |
581 | No output. Watch the exit status. | |
582 | .hP 1. | |
583 | All messages. | |
584 | .PP | |
585 | .B Warning! | |
fa54fe1e | 586 | All output written has been checked for authenticity. However, output |
77e4471a | 587 | can fail midway through for many reasons, and the resulting message may |
45c0fd36 | 588 | therefore be truncated. Don't rely on the output being complete until |
4224d0b9 | 589 | .B OK |
590 | is printed or | |
c65df279 | 591 | .B catcrypt decrypt |
fa54fe1e | 592 | exits successfully. |
c65df279 | 593 | .SS "encode" |
594 | The | |
595 | .B encode | |
596 | command encodes an input file according to one of the encodings | |
597 | described above in | |
598 | .BR ENCODINGS . | |
45c0fd36 | 599 | The input is read from the |
c65df279 | 600 | .I file |
601 | given on the command line, or from standard input if none is specified. | |
602 | Options provided are: | |
603 | .TP | |
cd6eca43 MW |
604 | .BI "\-p, \-\-progress" |
605 | Write a progress meter to standard error while processing large files. | |
606 | .TP | |
c65df279 | 607 | .BI "\-f, \-\-format " format |
608 | Produce output in | |
609 | .IR format . | |
610 | Run | |
611 | .B catcrypt show enc | |
612 | for a list of encoding formats. | |
613 | .TP | |
614 | .BI "\-b, \-\-boundary " label | |
615 | Set the PEM boundary string to | |
616 | .IR label ; | |
617 | i.e., assuming we're encoding in PEM format, the output will have | |
618 | .BI "\-\-\-\-\-BEGIN " label "\-\-\-\-\-" | |
619 | at the top and | |
620 | .BI "\-\-\-\-\-END " label "\-\-\-\-\-" | |
621 | at the bottom. The default | |
622 | .I label | |
623 | is | |
624 | .BR MESSAGE . | |
625 | .TP | |
626 | .BI "\-o, \-\-output " file | |
627 | Write output to | |
628 | .I file | |
629 | instead of to standard output. | |
630 | .SS "decode" | |
631 | The | |
632 | .B decode | |
633 | command decodes an input file encoded according to one of the encodings | |
634 | described above in | |
635 | .BR ENCODINGS . | |
45c0fd36 | 636 | The input is read from the |
c65df279 | 637 | .I file |
638 | given on the command line, or from standard input if none is specified. | |
639 | Options provided are: | |
640 | .TP | |
641 | .BI "\-f, \-\-format " format | |
642 | Decode input in | |
643 | .IR format . | |
644 | Run | |
645 | .B catcrypt show enc | |
646 | for a list of encoding formats. | |
647 | .TP | |
648 | .BI "\-b, \-\-boundary " label | |
649 | Set the PEM boundary string to | |
650 | .IR label ; | |
651 | i.e., assuming we're encoding in PEM format, start processing input | |
652 | between | |
653 | .BI "\-\-\-\-\-BEGIN " label "\-\-\-\-\-" | |
45c0fd36 | 654 | and |
c65df279 | 655 | .BI "\-\-\-\-\-END " label "\-\-\-\-\-" |
656 | lines. Without this option, | |
657 | .B catcrypt | |
658 | will start reading at the first plausible boundary string, and continue | |
659 | processing until it reaches the matching end boundary. | |
660 | .TP | |
cd6eca43 MW |
661 | .BI "\-p, \-\-progress" |
662 | Write a progress meter to standard error while processing large files. | |
663 | .TP | |
c65df279 | 664 | .BI "\-o, \-\-output " file |
665 | Write output to | |
666 | .I file | |
667 | instead of to standard output. | |
668 | .SH "SECURITY PROPERTIES" | |
669 | Assuming the security of the underlying primitive algorithms, the | |
670 | following security properties of the ciphertext hold. | |
671 | .hP \*o | |
672 | An adversary given the public key-encapsulation key and capable of | |
673 | requesting encryption of arbitrary plaintexts of his own devising is | |
674 | unable to decide whether he is given ciphertexts corresponding to his | |
675 | chosen plaintexts or random plaintexts of the same length. This holds | |
676 | even if the adversary is permitted to request decryption of any | |
677 | ciphertext other than one produced as a result of an encryption request. | |
678 | This property is called | |
679 | .BR IND-CCA2 . | |
680 | .hP \*o | |
681 | An adversary given the public key-encapsulation and verification keys, | |
682 | and capable of requesting encryption of arbitrary plaintext of his own | |
683 | devising is unable to produce a new ciphertext which will be accepted as | |
684 | genuine. This property is called | |
685 | .BR INT-CTXT . | |
686 | .hP \*o | |
687 | An adversary given the public key-encapsulation and verification keys, | |
688 | and capable of requesting encryption of arbitrary plaintext of his own | |
689 | devising is unable to decide whether the ciphertexts he is given are | |
690 | correctly signed. This property doesn't seem to have a name. | |
691 | .PP | |
692 | Not all is rosy. If you leak intermediate values during decryption then | |
693 | an adversary can construct a new correctly-signed message. Don't do | |
694 | that, then \(en leaking intermediate values often voids security | |
695 | warranties. But it does avoid the usual problem with separate signing | |
696 | and encryption that a careful leak by the recipient can produce evidence | |
697 | that you signed some incriminating message. | |
4224d0b9 | 698 | .PP |
699 | Note that | |
700 | .BR catcrypt 's | |
701 | signatures do | |
702 | .I not | |
703 | provide `non-repudiation' in any useful way. This is deliberate: the | |
704 | purpose of signing is to convince the recipient of the sender's | |
705 | identity, rather than to allow the recipient to persuade anyone else. | |
706 | Indeed, given an encrypted and signed message, the recipient can | |
707 | straightforwardly construct a new message, apparently from the same | |
708 | sender, and whose signature still verifies, but with arbitrarily chosen | |
709 | content. | |
c65df279 | 710 | .SH "CRYPTOGRAPHIC THEORY" |
711 | Encryption of a message proceeds as follows. | |
712 | .hP 0. | |
713 | Emit a header packet containing the key-ids for the key-encapsulation | |
714 | key, and signature key if any. | |
715 | .hP 1. | |
716 | Use the KEM to produce a public value and a shared secret the recipient | |
717 | will be able to extract from the public value using his private key. | |
718 | Emit a packet containing the public value. | |
719 | .hP 2. | |
720 | Hash the shared secret. Use the KDF to produce a pseudorandom keystream | |
721 | of indefinite length. | |
722 | .hP 3. | |
723 | Use the first bits of the keystream to key a symmetric encryption | |
724 | scheme; use the next bits to key a message authentication code. | |
725 | .hP 4. | |
726 | If we're signing the message then extract 1024 bytes from the keystream, | |
f9e51332 | 727 | sign the header and public value, and the keystream bytes; emit a packet |
728 | containing the signature. The signature packet doesn't contain the | |
729 | signed message, just the signature. | |
c65df279 | 730 | .hP 5. |
731 | Split the message into blocks. For each block, pick a random IV from | |
732 | the keystream, encrypt the block and emit a packet containing the | |
aaa2361e | 733 | IV, ciphertext, and a MAC tag over the ciphertext and a sequence number. |
734 | .hP 6. | |
735 | The last chunk is the encryption of an empty plaintext block. No | |
736 | previous plaintext block is empty. This lets us determine the | |
737 | difference between a complete file and one that's been maliciously | |
738 | truncated. | |
c65df279 | 739 | .PP |
740 | That's it. Nothing terribly controversial, really. | |
741 | .SH "SEE ALSO" | |
742 | .BR key (1), | |
fa54fe1e | 743 | .BR catsign (1), |
c65df279 | 744 | .BR dsig (1), |
745 | .BR hashsum (1), | |
746 | .BR keyring (5). | |
747 | .SH AUTHOR | |
f387fcb1 | 748 | Mark Wooding, <mdw@distorted.org.uk> |