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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 | |
66ff643c MW |
137 | .IR bulk \c |
138 | .RB [ \- \c | |
139 | .IR cipher ] \c | |
140 | .RB [ / \c | |
141 | .IR hash ]] | |
142 | or | |
143 | .IR kem \c | |
144 | .RB [ / \c | |
c65df279 | 145 | .IR cipher \c |
146 | .RB [ / \c | |
147 | .IR hash ]]. | |
148 | If a | |
149 | .B kem | |
150 | attribute is present on the key, then it must have this form; otherwise, | |
151 | the key's type must have the form | |
152 | .BR cckem- \c | |
153 | .IR kemalgspec . | |
154 | Algorithm selections are taken from appropriately-named attributes, or, | |
155 | failing that, from the | |
156 | .IR kemalgspec . | |
157 | .PP | |
158 | The key-encapsulation mechanism is chosen according to the setting of | |
159 | .I kem | |
160 | as follows. Run | |
161 | .B catcrypt show kem | |
162 | for a list of supported KEMs. | |
163 | .TP | |
164 | .B rsa | |
165 | This is Shoup's RSA-KEM (formerly Simple RSA); see | |
166 | .I | |
167 | A proposal for an ISO standard for public key encryption (version 2.0) | |
168 | available at | |
169 | .BR http://eprint.iacr.org/2000/060/ . | |
170 | Use the | |
171 | .B rsa | |
172 | algorithm of the | |
173 | .B key add | |
174 | command (see | |
175 | .BR key (1)) | |
176 | to generate the key. | |
177 | .TP | |
178 | .B dh | |
179 | This is standard Diffie-Hellman key exchange, hashing the resulting | |
180 | shared secret to form the key, as used in, e.g., DLIES (P1363a). | |
181 | Use the | |
182 | .B dh | |
183 | algorithm of the | |
184 | .B key add | |
185 | command, preferably with the | |
186 | .B \-LS | |
187 | options, to generate the key. | |
188 | .TP | |
189 | .B ec | |
190 | This is the elliptic-curve analogue of | |
b98200ad | 191 | .BR dh . |
192 | Use the | |
c65df279 | 193 | .B ec |
194 | algorithm of the | |
195 | .BR key (1)) | |
196 | command to generate the key. | |
02dfbd5b MW |
197 | .TP |
198 | .B symm | |
199 | This is a simple symmetric encapsulation scheme. It works by hashing a | |
200 | binary key with a randomly-generated salt. Use the | |
201 | .B binary | |
202 | algorithm of the | |
203 | .B key add | |
204 | command (see | |
205 | .BR key (1)) | |
206 | to generate the key. | |
fc2d44af MW |
207 | .TP |
208 | .B x25519 | |
209 | This is Bernstein's Curve25519, a fast Diffie-Hellman using a specific | |
210 | elliptic curve. | |
211 | Use the | |
212 | .B x25519 | |
213 | algorithm of the | |
214 | .B key add | |
215 | command | |
216 | (see | |
217 | .BR key (1)) | |
218 | to generate the key. | |
643eb1bb MW |
219 | .TP |
220 | .B x448 | |
221 | This is Hamburg's Curve25519, a strong Diffie-Hellman using a specific | |
222 | elliptic curve. | |
223 | Use the | |
224 | .B x448 | |
225 | algorithm of the | |
226 | .B key add | |
227 | command | |
228 | (see | |
229 | .BR key (1)) | |
230 | to generate the key. | |
c65df279 | 231 | .PP |
66ff643c MW |
232 | The bulk crypto transform is chosen based on the |
233 | .B bulk | |
234 | attribute on the key, or, failing that, | |
235 | from the | |
236 | .I bulk | |
237 | stated in the | |
238 | .IR kemalgspec . | |
239 | Run | |
240 | .B catcrypt show bulk | |
241 | for a list of supported bulk crypto transforms. | |
242 | .TP | |
243 | .B gencomp | |
244 | A generic composition of | |
245 | a cipher secure against chosen-plaintext attack, | |
246 | and a message authentication code. | |
247 | Makes use of | |
248 | .B cipher | |
249 | and | |
250 | .B mac | |
251 | attributes. | |
252 | This is the default transform. | |
d9d419b0 MW |
253 | .TP |
254 | .B naclbox | |
255 | Use Salsa20 or ChaCha and Poly1305 to secure the bulk data. | |
256 | This is nearly the same as the NaCl | |
257 | .B crypto_secretbox | |
258 | construction, | |
259 | except that | |
260 | .B catcrypt | |
261 | uses Salsa20 or ChaCha rather than XSalsa20, | |
262 | because it doesn't need the latter's extended nonce. | |
263 | The | |
264 | .B cipher | |
265 | attribute may be set to one of | |
266 | .BR salsa20 , | |
267 | .BR salsa20/12 , | |
268 | .BR salsa20/8 , | |
269 | .BR chacha20 , | |
270 | .BR chacha12 , | |
271 | or | |
272 | .BR chacha8 ; | |
273 | the default is | |
274 | .BR salsa20 . | |
66ff643c | 275 | .PP |
c65df279 | 276 | As well as the KEM itself, a number of supporting algorithms are used. |
277 | These are taken from appropriately named attributes on the key or, | |
278 | failing that, derived from other attributes as described below. | |
279 | .TP | |
280 | .B cipher | |
66ff643c MW |
281 | This is the symmetric encryption algorithm |
282 | used by the bulk data transform. | |
283 | If there is no | |
c65df279 | 284 | .B cipher |
285 | attribute then the | |
66ff643c | 286 | .I bulk |
c65df279 | 287 | in the |
288 | .I kemalgspec | |
289 | is used; if that it absent, then the default of | |
290 | .B blowfish-cbc | |
291 | is used. Run | |
292 | .B catcrypt show cipher | |
293 | for a list of supported symmetric encryption algorithms. | |
294 | .TP | |
295 | .B hash | |
296 | This is the hash function used to distil entropy from the shared secret | |
297 | constructed by the raw KEM. If there is no | |
298 | .B hash | |
299 | attribute then the | |
300 | .I hash | |
301 | in the | |
b98200ad | 302 | .I kemalgspec |
303 | is used; if that is absent then the default of | |
c65df279 | 304 | .B rmd160 |
305 | is used. Run | |
306 | .B catcrypt show hash | |
307 | for a list of supported symmetric encryption algorithms. | |
308 | .TP | |
309 | .B mac | |
66ff643c MW |
310 | This is the message authentication algorithm |
311 | used by the | |
312 | .B gencomp | |
313 | bulk data transform | |
314 | to ensure integrity of the encrypted message and | |
315 | defend against chosen-ciphertext attacks. | |
316 | If there is no | |
c65df279 | 317 | .B mac |
318 | attribute then | |
319 | .IB hash -hmac | |
320 | is chosen as a default. Run | |
321 | .B catcrypt show mac | |
322 | for a list of supported message authentication algorithms. | |
323 | .TP | |
324 | .B kdf | |
325 | This is the key derivation function used to stretch the hashed shared | |
326 | secret to a sufficient length to select symmetric encryption and | |
327 | authentication keys, initialization vectors and other necessary | |
328 | pseudorandom quantities. If there is no | |
329 | .B kdf | |
330 | attribute then | |
331 | .IB hash -mgf | |
332 | is chosen as a default. Run | |
333 | .B catcrypt show kdf | |
334 | for a list of supported key derivation functions. | |
335 | .B Caution! | |
336 | Not all supported functions have the required security features: don't | |
337 | override the default choice unless you know what you're doing. | |
338 | .SS "Signing keys" | |
339 | A | |
340 | .I sigalgspec | |
341 | has the form | |
342 | .IR sig \c | |
343 | .RB [ / \c | |
344 | .IR hash ]. | |
345 | If a | |
346 | .B sig | |
347 | attribute is present on the key, then it must have this form; otherwise, | |
348 | the key's type must have the form | |
349 | .BI ccsig- \c | |
350 | .IR sigalgspec . | |
351 | Algorithm selections are taken from appropriately-named attributes, or, | |
352 | failing that, from the | |
353 | .IR sigalgspec . | |
354 | .PP | |
355 | The signature algorithm is chosen according to the setting of | |
356 | .I sig | |
357 | as follows. Run | |
358 | .B catcrypt show sig | |
359 | for a list of supported signature algorithms. | |
360 | .TP | |
361 | .B rsapkcs1 | |
362 | This is almost the same as the RSASSA-PKCS1-v1_5 algorithm described in | |
363 | RFC3447; the difference is that the hash is left bare rather than being | |
45c0fd36 | 364 | wrapped in a DER-encoded |
c65df279 | 365 | .B DigestInfo |
366 | structure. This doesn't affect security since the key can only be used | |
367 | with the one hash function anyway, and dropping the DER wrapping permits | |
368 | rapid adoption of new hash functions. Regardless, use of this algorithm | |
369 | is not recommended, since the padding method has been shown vulnerable | |
370 | to attack. Use the | |
371 | .B rsa | |
372 | algorithm of the | |
373 | .B key add | |
374 | command (see | |
375 | .BR key (1)) | |
376 | to generate the key. | |
377 | .TP | |
378 | .B rsapss | |
379 | This is the RSASSA-PSS algorithm described in RFC3447. It is the | |
380 | preferred RSA-based signature scheme. Use the | |
381 | .B rsa | |
382 | algorithm of the | |
383 | .B key add | |
384 | command (see | |
385 | .BR key (1)) | |
386 | to generate the key. | |
387 | .TP | |
388 | .B dsa | |
45c0fd36 | 389 | This is the DSA algorithm described in FIPS180-1 and FIPS180-2. Use the |
c65df279 | 390 | .B dsa |
391 | algorithm of the | |
392 | .B key add | |
393 | command (see | |
394 | .BR key (1)) | |
395 | to generate the key. | |
396 | .TP | |
397 | .B ecdsa | |
398 | This is the ECDSA algorithm described in ANSI X9.62 and FIPS180-2. Use | |
399 | the | |
400 | .B ec | |
401 | algorithm of the | |
402 | .B key add | |
403 | command (see | |
404 | .BR key (1)) | |
405 | to generate the key. | |
406 | .TP | |
407 | .B kcdsa | |
408 | This is the revised KCDSA (Korean Certificate-based Digital Signature | |
409 | Algorithm) described in | |
410 | .I The Revised Version of KCDSA | |
411 | .RB ( http://dasan.sejong.ac.kr/~chlim/pub/kcdsa1.ps ). | |
412 | Use the | |
413 | .B dh | |
414 | algorithm of the | |
415 | .B key add | |
416 | command with the | |
417 | .B \-LS | |
418 | options (see | |
419 | .BR key (1)) | |
420 | to generate the key. | |
421 | .TP | |
422 | .B eckcdsa | |
423 | This is an unofficial elliptic-curve analogue of the KCDSA algorithm. | |
424 | Use the | |
425 | .B ec | |
426 | algorithm of the | |
427 | .B key add | |
428 | command (see | |
429 | .BR key (1)) | |
430 | to generate the key. | |
02dfbd5b | 431 | .TP |
d56fd9d1 MW |
432 | .B ed25519 |
433 | This is Bernstein, Duif, Lange, Schwabe, and Yang's Ed25519 algorithm. | |
434 | More specifically, this is HashEd25519 | |
435 | using the selected | |
436 | .B hash | |
437 | algorithm \(en by default | |
438 | .BR sha512 . | |
439 | Use the | |
440 | .B ed25519 | |
441 | algorithm of the | |
442 | .B key add | |
443 | command | |
444 | (see | |
445 | .BR key (1)) | |
446 | to generate the key. | |
447 | .TP | |
c578d5d8 MW |
448 | .B ed448 |
449 | This is Bernstein, Duif, Lange, Schwabe, and Yang's EdDSA algorithm, | |
450 | using Hamburg's Ed448-Goldilocks elliptic curve, | |
451 | as specified in RFC8032. | |
452 | More specifically, this is HashEd448 | |
453 | using the selected | |
454 | .B hash | |
455 | algorithm \(en by default | |
456 | .BR sha3-512 . | |
457 | Use the | |
458 | .B ed448 | |
459 | algorithm of the | |
460 | .B key add | |
461 | command | |
462 | (see | |
463 | .BR key (1)) | |
464 | to generate the key. | |
465 | .TP | |
02dfbd5b MW |
466 | .B mac |
467 | This uses a symmetric message-authentication algorithm rather than a | |
468 | digital signature. The precise message-authentication scheme used is | |
469 | determined by the | |
470 | .B mac | |
471 | attribute on the key, which defaults to | |
472 | .IB hash -hmac | |
473 | if unspecified. Use the | |
474 | .B binary | |
475 | algorithm of the | |
476 | .B key add | |
477 | command (see | |
478 | .BR key (1)) | |
479 | to generate the key. | |
c65df279 | 480 | .PP |
481 | As well as the signature algorithm itself, a hash function is used. | |
482 | This is taken from the | |
483 | .B hash | |
484 | attribute on the key, or, failing that, from the | |
485 | .I hash | |
486 | specified in the | |
487 | .IR sigalgspec , | |
488 | or, if that is absent, determined by the signature algorithm as follows. | |
489 | .hP \*o | |
490 | For | |
491 | .BR rsapkcs1 , | |
492 | .BR rsapss , | |
493 | .BR dsa , | |
494 | and | |
495 | .BR ecdsa , | |
496 | the default hash function is | |
497 | .BR sha . | |
498 | .hP \*o | |
499 | For | |
45c0fd36 | 500 | .BR kcdsa |
c65df279 | 501 | and |
502 | .BR eckcdsa , | |
503 | the default hash function is | |
504 | .BR has160 . | |
df8800f1 MW |
505 | For |
506 | .BR ed25519 , | |
507 | the default hash function is | |
508 | .BR sha512 . | |
c578d5d8 MW |
509 | For |
510 | .BR ed448 , | |
511 | the default hash function is | |
512 | .BR shake256 . | |
c65df279 | 513 | .PP |
514 | Run | |
515 | .B catcrypt show hash | |
516 | for a list of supported hash functions. | |
517 | .SH "ENCODINGS" | |
518 | Two encodings for the ciphertext are supported. | |
519 | .TP | |
520 | .B binary | |
521 | The raw format, which has the benefit of being smaller, but needs to be | |
522 | attached to mail messages and generally handled with care. | |
523 | .TP | |
524 | .B pem | |
525 | PEM-encapsulated Base-64 encoded text. This format can be included | |
526 | directly in email and picked out again automatically; but there is a | |
527 | 4-to-3 data expansion as a result. | |
528 | .SH "COMMAND REFERENCE" | |
529 | .SS help | |
530 | The | |
531 | .B help | |
532 | command behaves exactly as the | |
533 | .B \-\-help | |
534 | option. With no arguments, it shows an overview of | |
535 | .BR catcrypt 's | |
536 | options; with arguments, it describes the named subcommands. | |
537 | .SS show | |
538 | The | |
539 | .B show | |
540 | command prints various lists of tokens understood by | |
541 | .BR catcrypt . | |
542 | With no arguments, it prints all of the lists; with arguments, it prints | |
543 | just the named lists, in order. The recognized lists can be enumerated | |
544 | using the | |
545 | .VS | |
546 | catcrypt show list | |
547 | .VE | |
548 | command. The lists are as follows. | |
549 | .TP | |
550 | .B list | |
551 | The lists which can be enumerated by the | |
552 | .B show | |
553 | command. | |
554 | .TP | |
555 | .B kem | |
556 | The key-encapsulation algorithms which can be used in a | |
557 | key-encapsulation key's | |
558 | .B kem | |
559 | attribute. | |
560 | .TP | |
561 | .B cipher | |
562 | The symmetric encryption algorithms which can be used in a | |
563 | key-encapsulation key's | |
564 | .B cipher | |
565 | attribute. | |
566 | .TP | |
567 | .B mac | |
568 | The message authentication algorithms which can be used in a | |
569 | key-encapsulation key's | |
570 | .B mac | |
571 | attribute. | |
572 | .TP | |
573 | .B sig | |
574 | The signature algorithms which can be used in a signing key's | |
575 | .B sig | |
576 | attribute. | |
577 | .TP | |
578 | .B hash | |
579 | The hash functions which can be used in a key's | |
580 | .B hash | |
581 | attribute. | |
582 | .TP | |
583 | .B enc | |
45c0fd36 | 584 | The encodings which can be applied to encrypted messages; see |
c65df279 | 585 | .B ENCODINGS |
586 | above. | |
587 | .SS encrypt | |
588 | The | |
589 | .B encrypt | |
590 | command encrypts a file and writes out the appropriately-encoded | |
591 | ciphertext. By default, it reads from standard input and writes to | |
592 | standard output. If a filename argument is given, this file is read | |
593 | instead (as binary data). | |
594 | .PP | |
595 | The following options are recognized. | |
596 | .TP | |
597 | .B "\-a, \-\-armour" | |
598 | Produce ASCII-armoured output. This is equivalent to specifying | |
599 | .BR "\-f pem" . | |
600 | The variant spelling | |
601 | .B "\-\-armor" | |
602 | is also accepted. | |
603 | .TP | |
604 | .BI "\-f, \-\-format " format | |
605 | Produce output encoded according to | |
606 | .IR format . | |
607 | .TP | |
608 | .BI "\-k, \-\-key " tag | |
609 | Use the key-encapsulation key named | |
610 | .I tag | |
611 | in the current keyring; the default key is | |
612 | .BR ccrypt . | |
613 | .TP | |
cd6eca43 MW |
614 | .BI "\-p, \-\-progress" |
615 | Write a progress meter to standard error while processing large files. | |
616 | .TP | |
c65df279 | 617 | .BI "\-s, \-\-sign-key " tag |
618 | Use the signature key named | |
619 | .I tag | |
620 | in the current keyring; the default is not to sign the ciphertext. | |
621 | .TP | |
622 | .BI "\-o, \-\-ouptut " file | |
623 | Write output to | |
624 | .I file | |
625 | rather than to standard output. | |
946c3f72 | 626 | .TP |
627 | .B "\-C, \-\-nocheck" | |
628 | Don't check the public key for validity. This makes encryption go much | |
629 | faster, but at the risk of using a duff key. | |
c65df279 | 630 | .SS decrypt |
631 | The | |
632 | .B decrypt | |
633 | command decrypts a ciphertext and writes out the plaintext. By default, | |
634 | it reads from standard input and writes to standard output. If a | |
635 | filename argument is given, this file is read instead. | |
636 | .PP | |
637 | The following options are recognized. | |
638 | .TP | |
639 | .B "\-a, \-\-armour" | |
fa54fe1e | 640 | Read ASCII-armoured input. This is equivalent to specifying |
c65df279 | 641 | .BR "\-f pem" . |
642 | The variant spelling | |
643 | .B "\-\-armor" | |
644 | is also accepted. | |
645 | .TP | |
fa54fe1e | 646 | .B "\-b, \-\-buffer" |
647 | Buffer plaintext data until we're sure we've got it all. This is forced | |
648 | on if output is to stdout, but is always available as an option. | |
649 | .TP | |
c65df279 | 650 | .BI "\-f, \-\-format " format |
651 | Read input encoded according to | |
652 | .IR format . | |
653 | .TP | |
cd6eca43 MW |
654 | .BI "\-p, \-\-progress" |
655 | Write a progress meter to standard error while processing large files. | |
656 | .TP | |
c65df279 | 657 | .B "\-v, \-\-verbose" |
658 | Produce more verbose messages. See below for the messages produced | |
659 | during decryption. The default verbosity level is 1. (Currently this | |
660 | is the most verbose setting. This might not be the case always.) | |
661 | .TP | |
662 | .B "\-q, \-\-quiet" | |
663 | Produce fewer messages. | |
664 | .TP | |
665 | .BI "\-o, \-\-output " file | |
666 | Write output to | |
667 | .I file | |
668 | instead of to standard output. The file is written in binary mode. | |
669 | Fixing line-end conventions is your problem; there are lots of good | |
670 | tools for dealing with it. | |
946c3f72 | 671 | .TP |
672 | .B "\-C, \-\-nocheck" | |
673 | Don't check the private key for validity. This makes decryption go much | |
674 | faster, but at the risk of using a duff key, and possibly leaking | |
675 | information about the private key. | |
c65df279 | 676 | .PP |
677 | Output is written to standard output in a machine-readable format. | |
678 | Major problems cause the program to write a diagnostic to standard error | |
679 | and exit nonzero as usual. The quantity of output varies depending on | |
680 | the verbosity level and whether the plaintext is also being written to | |
fa54fe1e | 681 | standard output. Output lines begin with a keyword: |
c65df279 | 682 | .TP |
683 | .BI "FAIL " reason | |
684 | An error prevented decryption. The program will exit nonzero. | |
685 | .TP | |
686 | .BI "WARN " reason | |
687 | .B catcrypt | |
688 | encountered a situation which may or may not invalidate the decryption. | |
45c0fd36 | 689 | .TP |
c65df279 | 690 | .BI "OK " message |
691 | Decryption was successful. This is only produced if main output is | |
692 | being sent somewhere other than standard output. | |
693 | .TP | |
694 | .B "DATA" | |
695 | The plaintext follows, starting just after the next newline character or | |
b98200ad | 696 | sequence. This is only produced if main output is also being sent to |
fa54fe1e | 697 | standard output. |
c65df279 | 698 | .TP |
699 | .BI "INFO " note | |
700 | Any other information. | |
701 | .PP | |
702 | The information written at the various verbosity levels is as follows. | |
703 | .hP 0. | |
704 | No output. Watch the exit status. | |
705 | .hP 1. | |
706 | All messages. | |
707 | .PP | |
708 | .B Warning! | |
fa54fe1e | 709 | All output written has been checked for authenticity. However, output |
77e4471a | 710 | can fail midway through for many reasons, and the resulting message may |
45c0fd36 | 711 | therefore be truncated. Don't rely on the output being complete until |
4224d0b9 | 712 | .B OK |
713 | is printed or | |
c65df279 | 714 | .B catcrypt decrypt |
fa54fe1e | 715 | exits successfully. |
c65df279 | 716 | .SS "encode" |
717 | The | |
718 | .B encode | |
719 | command encodes an input file according to one of the encodings | |
720 | described above in | |
721 | .BR ENCODINGS . | |
45c0fd36 | 722 | The input is read from the |
c65df279 | 723 | .I file |
724 | given on the command line, or from standard input if none is specified. | |
725 | Options provided are: | |
726 | .TP | |
cd6eca43 MW |
727 | .BI "\-p, \-\-progress" |
728 | Write a progress meter to standard error while processing large files. | |
729 | .TP | |
c65df279 | 730 | .BI "\-f, \-\-format " format |
731 | Produce output in | |
732 | .IR format . | |
733 | Run | |
734 | .B catcrypt show enc | |
735 | for a list of encoding formats. | |
736 | .TP | |
737 | .BI "\-b, \-\-boundary " label | |
738 | Set the PEM boundary string to | |
739 | .IR label ; | |
740 | i.e., assuming we're encoding in PEM format, the output will have | |
741 | .BI "\-\-\-\-\-BEGIN " label "\-\-\-\-\-" | |
742 | at the top and | |
743 | .BI "\-\-\-\-\-END " label "\-\-\-\-\-" | |
744 | at the bottom. The default | |
745 | .I label | |
746 | is | |
747 | .BR MESSAGE . | |
748 | .TP | |
749 | .BI "\-o, \-\-output " file | |
750 | Write output to | |
751 | .I file | |
752 | instead of to standard output. | |
753 | .SS "decode" | |
754 | The | |
755 | .B decode | |
756 | command decodes an input file encoded according to one of the encodings | |
757 | described above in | |
758 | .BR ENCODINGS . | |
45c0fd36 | 759 | The input is read from the |
c65df279 | 760 | .I file |
761 | given on the command line, or from standard input if none is specified. | |
762 | Options provided are: | |
763 | .TP | |
764 | .BI "\-f, \-\-format " format | |
765 | Decode input in | |
766 | .IR format . | |
767 | Run | |
768 | .B catcrypt show enc | |
769 | for a list of encoding formats. | |
770 | .TP | |
771 | .BI "\-b, \-\-boundary " label | |
772 | Set the PEM boundary string to | |
773 | .IR label ; | |
774 | i.e., assuming we're encoding in PEM format, start processing input | |
775 | between | |
776 | .BI "\-\-\-\-\-BEGIN " label "\-\-\-\-\-" | |
45c0fd36 | 777 | and |
c65df279 | 778 | .BI "\-\-\-\-\-END " label "\-\-\-\-\-" |
779 | lines. Without this option, | |
780 | .B catcrypt | |
781 | will start reading at the first plausible boundary string, and continue | |
782 | processing until it reaches the matching end boundary. | |
783 | .TP | |
cd6eca43 MW |
784 | .BI "\-p, \-\-progress" |
785 | Write a progress meter to standard error while processing large files. | |
786 | .TP | |
c65df279 | 787 | .BI "\-o, \-\-output " file |
788 | Write output to | |
789 | .I file | |
790 | instead of to standard output. | |
791 | .SH "SECURITY PROPERTIES" | |
792 | Assuming the security of the underlying primitive algorithms, the | |
793 | following security properties of the ciphertext hold. | |
794 | .hP \*o | |
795 | An adversary given the public key-encapsulation key and capable of | |
796 | requesting encryption of arbitrary plaintexts of his own devising is | |
797 | unable to decide whether he is given ciphertexts corresponding to his | |
798 | chosen plaintexts or random plaintexts of the same length. This holds | |
799 | even if the adversary is permitted to request decryption of any | |
800 | ciphertext other than one produced as a result of an encryption request. | |
801 | This property is called | |
802 | .BR IND-CCA2 . | |
803 | .hP \*o | |
804 | An adversary given the public key-encapsulation and verification keys, | |
805 | and capable of requesting encryption of arbitrary plaintext of his own | |
806 | devising is unable to produce a new ciphertext which will be accepted as | |
807 | genuine. This property is called | |
808 | .BR INT-CTXT . | |
809 | .hP \*o | |
810 | An adversary given the public key-encapsulation and verification keys, | |
811 | and capable of requesting encryption of arbitrary plaintext of his own | |
812 | devising is unable to decide whether the ciphertexts he is given are | |
813 | correctly signed. This property doesn't seem to have a name. | |
814 | .PP | |
815 | Not all is rosy. If you leak intermediate values during decryption then | |
816 | an adversary can construct a new correctly-signed message. Don't do | |
817 | that, then \(en leaking intermediate values often voids security | |
818 | warranties. But it does avoid the usual problem with separate signing | |
819 | and encryption that a careful leak by the recipient can produce evidence | |
820 | that you signed some incriminating message. | |
4224d0b9 | 821 | .PP |
822 | Note that | |
823 | .BR catcrypt 's | |
824 | signatures do | |
825 | .I not | |
826 | provide `non-repudiation' in any useful way. This is deliberate: the | |
827 | purpose of signing is to convince the recipient of the sender's | |
828 | identity, rather than to allow the recipient to persuade anyone else. | |
829 | Indeed, given an encrypted and signed message, the recipient can | |
830 | straightforwardly construct a new message, apparently from the same | |
831 | sender, and whose signature still verifies, but with arbitrarily chosen | |
832 | content. | |
c65df279 | 833 | .SH "CRYPTOGRAPHIC THEORY" |
834 | Encryption of a message proceeds as follows. | |
835 | .hP 0. | |
836 | Emit a header packet containing the key-ids for the key-encapsulation | |
837 | key, and signature key if any. | |
838 | .hP 1. | |
839 | Use the KEM to produce a public value and a shared secret the recipient | |
840 | will be able to extract from the public value using his private key. | |
841 | Emit a packet containing the public value. | |
842 | .hP 2. | |
843 | Hash the shared secret. Use the KDF to produce a pseudorandom keystream | |
844 | of indefinite length. | |
845 | .hP 3. | |
846 | Use the first bits of the keystream to key a symmetric encryption | |
847 | scheme; use the next bits to key a message authentication code. | |
848 | .hP 4. | |
849 | If we're signing the message then extract 1024 bytes from the keystream, | |
f9e51332 | 850 | sign the header and public value, and the keystream bytes; emit a packet |
851 | containing the signature. The signature packet doesn't contain the | |
852 | signed message, just the signature. | |
c65df279 | 853 | .hP 5. |
854 | Split the message into blocks. For each block, pick a random IV from | |
855 | the keystream, encrypt the block and emit a packet containing the | |
aaa2361e | 856 | IV, ciphertext, and a MAC tag over the ciphertext and a sequence number. |
857 | .hP 6. | |
858 | The last chunk is the encryption of an empty plaintext block. No | |
859 | previous plaintext block is empty. This lets us determine the | |
860 | difference between a complete file and one that's been maliciously | |
861 | truncated. | |
c65df279 | 862 | .PP |
863 | That's it. Nothing terribly controversial, really. | |
864 | .SH "SEE ALSO" | |
865 | .BR key (1), | |
fa54fe1e | 866 | .BR catsign (1), |
c65df279 | 867 | .BR dsig (1), |
868 | .BR hashsum (1), | |
869 | .BR keyring (5). | |
870 | .SH AUTHOR | |
f387fcb1 | 871 | Mark Wooding, <mdw@distorted.org.uk> |