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1 .\" Copyright (c) 1991, 1993
2 .\" The Regents of the University of California. All rights reserved.
3 .\"
4 .\" This code is derived from software contributed to Berkeley by
5 .\" Matt Bishop of Dartmouth College.
6 .\"
7 .\" Redistribution and use in source and binary forms, with or without
8 .\" modification, are permitted provided that the following conditions
9 .\" are met:
10 .\" 1. Redistributions of source code must retain the above copyright
11 .\" notice, this list of conditions and the following disclaimer.
12 .\" 2. Redistributions in binary form must reproduce the above copyright
13 .\" notice, this list of conditions and the following disclaimer in the
14 .\" documentation and/or other materials provided with the distribution.
15 .\" 3. All advertising materials mentioning features or use of this software
16 .\" must display the following acknowledgement:
17 .\" This product includes software developed by the University of
18 .\" California, Berkeley and its contributors.
19 .\" 4. Neither the name of the University nor the names of its contributors
20 .\" may be used to endorse or promote products derived from this software
21 .\" without specific prior written permission.
22 .\"
23 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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34 .\"
35 .\" @(#)bdes.1 8.1 (Berkeley) 6/29/93
36 .\" $FreeBSD$
37 .\"
38 .Dd June 29, 1993
39 .Dt BDES 1
40 .Os
41 .Sh NAME
42 .Nm bdes
43 .Nd "encrypt/decrypt using the Data Encryption Standard (DES)"
44 .Sh SYNOPSIS
45 .Nm
46 .Op Fl abdp
47 .Op Fl F Ar N
48 .Op Fl f Ar N
49 .Op Fl k Ar key
50 .Op Fl m Ar N
51 .Op Fl o Ar N
52 .Op Fl v Ar vector
53 .Sh DESCRIPTION
54 The
55 .Nm
56 utility implements all
57 .Tn DES
58 modes of operation described in
59 .%T "FIPS PUB 81" ,
60 including alternative cipher feedback mode and both authentication
61 modes.
62 The
63 .Nm
64 utility reads from the standard input
65 and writes to the standard output.
66 By default,
67 the input is encrypted
68 using cipher block chaining (CBC) mode.
69 Using the same key
70 for encryption and decryption
71 preserves plain text.
72 .Pp
73 All modes but the electronic code book (ECB) mode
74 require an initialization vector;
75 if none is supplied,
76 the zero vector is used.
77 If no
78 .Ar key
79 is specified on the command line,
80 the user is prompted for one (see
81 .Xr getpass 3
82 for more details).
83 .Pp
84 The options are as follows:
85 .Bl -tag -width indent
86 .It Fl a
87 The key and initialization vector strings
88 are to be taken as
89 .Tn ASCII ,
90 suppressing the special interpretation given to leading
91 .Dq Li 0X ,
92 .Dq Li 0x ,
93 .Dq Li 0B ,
94 and
95 .Dq Li 0b
96 characters.
97 This flag applies to
98 .Em both
99 the key and initialization vector.
100 .It Fl b
101 Use ECB mode.
102 .It Fl d
103 Decrypt the input.
104 .It Fl F Ar N
105 Use
106 .Ar N Ns \-bit
107 alternative CFB mode.
108 Currently
109 .Ar N
110 must be a multiple of 7
111 between 7 and 56 inclusive
112 (this does not conform to the alternative CFB mode specification).
113 .It Fl f Ar N
114 Use
115 .Ar N Ns \-bit
116 CFB mode.
117 Currently
118 .Ar N
119 must be a multiple of 8 between 8 and 64 inclusive (this does not conform
120 to the standard CFB mode specification).
121 .It Fl k Ar key
122 Use
123 .Ar key
124 as the cryptographic key.
125 .It Fl m Ar N
126 Compute a message authentication code (MAC) of
127 .Ar N
128 bits on the input.
129 The value of
130 .Ar N
131 must be between 1 and 64 inclusive; if
132 .Ar N
133 is not a multiple of 8,
134 enough 0 bits will be added
135 to pad the MAC length
136 to the nearest multiple of 8.
137 Only the MAC is output.
138 MACs are only available
139 in CBC mode
140 or in CFB mode.
141 .It Fl o Ar N
142 Use
143 .Ar N Ns \-bit
144 ouput feedback (OFB) mode.
145 Currently
146 .Ar N
147 must be a multiple of 8 between 8 and 64 inclusive (this does not conform
148 to the OFB mode specification).
149 .It Fl p
150 Disable the resetting of the parity bit.
151 This flag forces
152 the parity bit of the key
153 to be used as typed,
154 rather than making
155 each character be of odd parity.
156 It is used only if the key is given in
157 .Tn ASCII .
158 .It Fl v Ar vector
159 Set the initialization vector to
160 .Ar vector ;
161 the vector is interpreted in the same way as the key.
162 The vector is ignored in ECB mode.
163 .El
164 .Pp
165 The key and initialization vector
166 are taken as sequences of
167 .Tn ASCII
168 characters which are then mapped
169 into their bit representations.
170 If either begins with
171 .Dq Li 0X
172 or
173 .Dq Li 0x ,
174 that one is taken
175 as a sequence of hexadecimal digits
176 indicating the bit pattern;
177 if either begins with
178 .Dq Li 0B
179 or
180 .Dq Li 0b ,
181 that one is taken
182 as a sequence of binary digits
183 indicating the bit pattern.
184 In either case,
185 only the leading 64 bits
186 of the key or initialization vector
187 are used,
188 and if fewer than 64 bits are provided,
189 enough 0 bits are appended
190 to pad the key to 64 bits.
191 .Pp
192 According to the
193 .Tn DES
194 standard,
195 the low-order bit of each character
196 in the key string is deleted.
197 Since most
198 .Tn ASCII
199 representations
200 set the high-order bit to 0,
201 simply deleting the low-order bit
202 effectively reduces the size of the key space
203 from 2^56 to 2^48 keys.
204 To prevent this,
205 the high-order bit must be a function
206 depending in part upon the low-order bit;
207 so,
208 the high-order bit is set
209 to whatever value gives odd parity.
210 This preserves the key space size.
211 Note this resetting of the parity bit is
212 .Em not
213 done if the key
214 is given in binary or hex,
215 and can be disabled for
216 .Tn ASCII
217 keys as well.
218 .Pp
219 The
220 .Tn DES
221 is considered a very strong cryptosystem,
222 and other than table lookup attacks,
223 key search attacks,
224 and Hellman's time-memory tradeoff
225 (all of which are very expensive and time-consuming),
226 no cryptanalytic methods
227 for breaking the
228 .Tn DES
229 are known in the open literature.
230 No doubt the choice of keys
231 and key security
232 are the most vulnerable aspect of
233 .Nm .
234 .Sh IMPLEMENTATION NOTES
235 For implementors wishing to write
236 software compatible with this program,
237 the following notes are provided.
238 This software is believed
239 to be compatible with the implementation
240 of the data encryption standard
241 distributed by Sun Microsystems, Inc.
242 .Pp
243 In the ECB and CBC modes,
244 plaintext is encrypted in units of 64 bits
245 (8 bytes, also called a block).
246 To ensure that the plaintext file
247 is encrypted correctly,
248 .Nm
249 will (internally) append from 1 to 8 bytes,
250 the last byte containing an integer
251 stating how many bytes of that final block
252 are from the plaintext file,
253 and encrypt the resulting block.
254 Hence,
255 when decrypting,
256 the last block may contain from 0 to 7 characters
257 present in the plaintext file,
258 and the last byte tells how many.
259 Note that if during decryption
260 the last byte of the file
261 does not contain an integer between 0 and 7,
262 either the file has been corrupted
263 or an incorrect key has been given.
264 A similar mechanism is used
265 for the OFB and CFB modes,
266 except that those
267 simply require the length of the input
268 to be a multiple of the mode size,
269 and the final byte contains an integer
270 between 0 and one less than the number
271 of bytes being used as the mode.
272 (This was another reason
273 that the mode size must be
274 a multiple of 8 for those modes.)
275 .Pp
276 Unlike Sun's implementation,
277 unused bytes of that last block
278 are not filled with random data,
279 but instead contain
280 what was in those byte positions
281 in the preceding block.
282 This is quicker and more portable,
283 and does not weaken the encryption significantly.
284 .Pp
285 If the key is entered in
286 .Tn ASCII ,
287 the parity bits of the key characters
288 are set so that each key character
289 is of odd parity.
290 Unlike Sun's implementation,
291 it is possible to enter binary or hexadecimal
292 keys on the command line,
293 and if this is done,
294 the parity bits are
295 .Em not
296 reset.
297 This allows testing
298 using arbitrary bit patterns as keys.
299 .Pp
300 The Sun implementation
301 always uses an initialization vector of 0
302 (that is, all zeroes).
303 By default,
304 .Nm
305 does too,
306 but this may be changed
307 from the command line.
308 .Sh SEE ALSO
309 .Xr getpass 3
310 .Rs
311 .%T "Data Encryption Standard"
312 .%R "Federal Information Processing Standard #46"
313 .%Q "National Bureau of Standards, U.S. Department of Commerce, Washington DC"
314 .%D "January 1977"
315 .Re
316 .Rs
317 .%T "DES Modes of Operation"
318 .%R "Federal Information Processing Standard #81"
319 .%Q "National Bureau of Standards, U.S. Department of Commerce, Washington DC"
320 .%D "December 1980"
321 .Re
322 .Rs
323 .%A "Dorothy Denning"
324 .%B "Cryptography and Data Security"
325 .%Q "Addison-Wesley Publishing Co., Reading, MA"
326 .%D 1982
327 .Re
328 .Rs
329 .%A "Matt Bishop"
330 .%T "Implementation Notes on bdes(1)"
331 .%R "Technical Report PCS-TR-91-158"
332 .%Q "Department of Mathematics and Computer Science, Dartmouth College, Hanover, NH 03755"
333 .%D "April 1991"
334 .Re
335 .Sh DISCLAIMER
336 .Bd -literal
337 THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
338 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
339 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
340 ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
341 FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
342 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
343 OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
344 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
345 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
346 OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
347 SUCH DAMAGE.
348 .Ed
349 .Sh BUGS
350 There is a controversy raging over whether the
351 .Tn DES
352 will still be secure
353 in a few years.
354 The advent of special-purpose hardware
355 could reduce the cost of any of the
356 methods of attack named above
357 so that they are no longer
358 computationally infeasible.
359 .Pp
360 As the key or key schedule
361 is stored in memory,
362 the encryption can be
363 compromised if memory is readable.
364 Additionally,
365 programs which display programs' arguments
366 may compromise the key and initialization vector,
367 if they are specified on the command line.
368 To avoid this
369 .Nm
370 overwrites its arguments,
371 however,
372 the obvious race
373 cannot currently be avoided.
374 .Pp
375 Certain specific keys
376 should be avoided
377 because they introduce
378 potential weaknesses;
379 these keys,
380 called the
381 .Em weak
382 and
383 .Em semiweak
384 keys, are (in hex notation, where
385 .Ar p
386 is either 0 or 1, and
387 .Ar P
388 is either
389 .Ql e
390 or
391 .Ql f ) :
392 .Bl -column "0x0p0p0p0p0p0p0p0p" -offset indent
393 .It "0x0p0p0p0p0p0p0p0p 0x0p1P0p1P0p0P0p0P"
394 .It "0x0pep0pep0pfp0pfp 0x0pfP0pfP0pfP0pfP"
395 .It "0x1P0p1P0p0P0p0P0p 0x1P1P1P1P0P0P0P0P"
396 .It "0x1Pep1Pep0Pfp0Pfp 0x1PfP1PfP0PfP0PfP"
397 .It "0xep0pep0pfp0pfp0p 0xep1Pep1pfp0Pfp0P"
398 .It "0xepepepepepepepep 0xepfPepfPfpfPfpfP"
399 .It "0xfP0pfP0pfP0pfP0p 0xfP1PfP1PfP0PfP0P"
400 .It "0xfPepfPepfPepfPep 0xfPfPfPfPfPfPfPfP"
401 .El
402 .Pp
403 This is inherent in the
404 .Tn DES
405 algorithm;
406 see
407 .Rs
408 .%A Moore
409 .%A Simmons
410 .%T "Cycle structure of the DES with weak and semi-weak keys"
411 .%B "Advances in Cryptology \- Crypto '86 Proceedings"
412 .%Q "Springer-Verlag New York"
413 .%D 1987
414 .%P "pp. 9-32"
415 .Re