1 .. SPDX-License-Identifier: GPL-2.0
2 .. include:: <isonum.txt>
3
4 ===========================================
5 Fast & Portable DES encryption & decryption
6 ===========================================
7
8 .. note::
9
10 Below is the original README file from the descore.shar package,
11 converted to ReST format.
12
13 ------------------------------------------------------------------------------
14
15 des - fast & portable DES encryption & decryption.
16
17 Copyright |copy| 1992 Dana L. How
18
19 This program is free software; you can redistribute it and/or modify
20 it under the terms of the GNU Library General Public License as published by
21 the Free Software Foundation; either version 2 of the License, or
22 (at your option) any later version.
23
24 This program is distributed in the hope that it will be useful,
25 but WITHOUT ANY WARRANTY; without even the implied warranty of
26 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
27 GNU Library General Public License for more details.
28
29 You should have received a copy of the GNU Library General Public License
30 along with this program; if not, write to the Free Software
31 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
32
33 Author's address: how@isl.stanford.edu
34
35 .. README,v 1.15 1992/05/20 00:25:32 how E
36
37 ==>> To compile after untarring/unsharring, just ``make`` <<==
38
39 This package was designed with the following goals:
40
41 1. Highest possible encryption/decryption PERFORMANCE.
42 2. PORTABILITY to any byte-addressable host with a 32bit unsigned C type
43 3. Plug-compatible replacement for KERBEROS's low-level routines.
44
45 This second release includes a number of performance enhancements for
46 register-starved machines. My discussions with Richard Outerbridge,
47 71755.204@compuserve.com, sparked a number of these enhancements.
48
49 To more rapidly understand the code in this package, inspect desSmallFips.i
50 (created by typing ``make``) BEFORE you tackle desCode.h. The latter is set
51 up in a parameterized fashion so it can easily be modified by speed-daemon
52 hackers in pursuit of that last microsecond. You will find it more
53 illuminating to inspect one specific implementation,
54 and then move on to the common abstract skeleton with this one in mind.
55
56
57 performance comparison to other available des code which i could
58 compile on a SPARCStation 1 (cc -O4, gcc -O2):
59
60 this code (byte-order independent):
61
62 - 30us per encryption (options: 64k tables, no IP/FP)
63 - 33us per encryption (options: 64k tables, FIPS standard bit ordering)
64 - 45us per encryption (options: 2k tables, no IP/FP)
65 - 48us per encryption (options: 2k tables, FIPS standard bit ordering)
66 - 275us to set a new key (uses 1k of key tables)
67
68 this has the quickest encryption/decryption routines i've seen.
69 since i was interested in fast des filters rather than crypt(3)
70 and password cracking, i haven't really bothered yet to speed up
71 the key setting routine. also, i have no interest in re-implementing
72 all the other junk in the mit kerberos des library, so i've just
73 provided my routines with little stub interfaces so they can be
74 used as drop-in replacements with mit's code or any of the mit-
75 compatible packages below. (note that the first two timings above
76 are highly variable because of cache effects).
77
78 kerberos des replacement from australia (version 1.95):
79
80 - 53us per encryption (uses 2k of tables)
81 - 96us to set a new key (uses 2.25k of key tables)
82
83 so despite the author's inclusion of some of the performance
84 improvements i had suggested to him, this package's
85 encryption/decryption is still slower on the sparc and 68000.
86 more specifically, 19-40% slower on the 68020 and 11-35% slower
87 on the sparc, depending on the compiler;
88 in full gory detail (ALT_ECB is a libdes variant):
89
90 =============== ============== =============== =================
91 compiler machine desCore libdes ALT_ECB slower by
92 =============== ============== =============== =================
93 gcc 2.1 -O2 Sun 3/110 304 uS 369.5uS 461.8uS 22%
94 cc -O1 Sun 3/110 336 uS 436.6uS 399.3uS 19%
95 cc -O2 Sun 3/110 360 uS 532.4uS 505.1uS 40%
96 cc -O4 Sun 3/110 365 uS 532.3uS 505.3uS 38%
97 gcc 2.1 -O2 Sun 4/50 48 uS 53.4uS 57.5uS 11%
98 cc -O2 Sun 4/50 48 uS 64.6uS 64.7uS 35%
99 cc -O4 Sun 4/50 48 uS 64.7uS 64.9uS 35%
100 =============== ============== =============== =================
101
102 (my time measurements are not as accurate as his).
103
104 the comments in my first release of desCore on version 1.92:
105
106 - 68us per encryption (uses 2k of tables)
107 - 96us to set a new key (uses 2.25k of key tables)
108
109 this is a very nice package which implements the most important
110 of the optimizations which i did in my encryption routines.
111 it's a bit weak on common low-level optimizations which is why
112 it's 39%-106% slower. because he was interested in fast crypt(3) and
113 password-cracking applications, he also used the same ideas to
114 speed up the key-setting routines with impressive results.
115 (at some point i may do the same in my package). he also implements
116 the rest of the mit des library.
117
118 (code from eay@psych.psy.uq.oz.au via comp.sources.misc)
119
120 fast crypt(3) package from denmark:
121
122 the des routine here is buried inside a loop to do the
123 crypt function and i didn't feel like ripping it out and measuring
124 performance. his code takes 26 sparc instructions to compute one
125 des iteration; above, Quick (64k) takes 21 and Small (2k) takes 37.
126 he claims to use 280k of tables but the iteration calculation seems
127 to use only 128k. his tables and code are machine independent.
128
129 (code from glad@daimi.aau.dk via alt.sources or comp.sources.misc)
130
131 swedish reimplementation of Kerberos des library
132
133 - 108us per encryption (uses 34k worth of tables)
134 - 134us to set a new key (uses 32k of key tables to get this speed!)
135
136 the tables used seem to be machine-independent;
137 he seems to have included a lot of special case code
138 so that, e.g., ``long`` loads can be used instead of 4 ``char`` loads
139 when the machine's architecture allows it.
140
141 (code obtained from chalmers.se:pub/des)
142
143 crack 3.3c package from england:
144
145 as in crypt above, the des routine is buried in a loop. it's
146 also very modified for crypt. his iteration code uses 16k
147 of tables and appears to be slow.
148
149 (code obtained from aem@aber.ac.uk via alt.sources or comp.sources.misc)
150
151 ``highly optimized`` and tweaked Kerberos/Athena code (byte-order dependent):
152
153 - 165us per encryption (uses 6k worth of tables)
154 - 478us to set a new key (uses <1k of key tables)
155
156 so despite the comments in this code, it was possible to get
157 faster code AND smaller tables, as well as making the tables
158 machine-independent.
159 (code obtained from prep.ai.mit.edu)
160
161 UC Berkeley code (depends on machine-endedness):
162 - 226us per encryption
163 - 10848us to set a new key
164
165 table sizes are unclear, but they don't look very small
166 (code obtained from wuarchive.wustl.edu)
167
168
169 motivation and history
170 ======================
171
172 a while ago i wanted some des routines and the routines documented on sun's
173 man pages either didn't exist or dumped core. i had heard of kerberos,
174 and knew that it used des, so i figured i'd use its routines. but once
175 i got it and looked at the code, it really set off a lot of pet peeves -
176 it was too convoluted, the code had been written without taking
177 advantage of the regular structure of operations such as IP, E, and FP
178 (i.e. the author didn't sit down and think before coding),
179 it was excessively slow, the author had attempted to clarify the code
180 by adding MORE statements to make the data movement more ``consistent``
181 instead of simplifying his implementation and cutting down on all data
182 movement (in particular, his use of L1, R1, L2, R2), and it was full of
183 idiotic ``tweaks`` for particular machines which failed to deliver significant
184 speedups but which did obfuscate everything. so i took the test data
185 from his verification program and rewrote everything else.
186
187 a while later i ran across the great crypt(3) package mentioned above.
188 the fact that this guy was computing 2 sboxes per table lookup rather
189 than one (and using a MUCH larger table in the process) emboldened me to
190 do the same - it was a trivial change from which i had been scared away
191 by the larger table size. in his case he didn't realize you don't need to keep
192 the working data in TWO forms, one for easy use of half the sboxes in
193 indexing, the other for easy use of the other half; instead you can keep
194 it in the form for the first half and use a simple rotate to get the other
195 half. this means i have (almost) half the data manipulation and half
196 the table size. in fairness though he might be encoding something particular
197 to crypt(3) in his tables - i didn't check.
198
199 i'm glad that i implemented it the way i did, because this C version is
200 portable (the ifdef's are performance enhancements) and it is faster
201 than versions hand-written in assembly for the sparc!
202
203
204 porting notes
205 =============
206
207 one thing i did not want to do was write an enormous mess
208 which depended on endedness and other machine quirks,
209 and which necessarily produced different code and different lookup tables
210 for different machines. see the kerberos code for an example
211 of what i didn't want to do; all their endedness-specific ``optimizations``
212 obfuscate the code and in the end were slower than a simpler machine
213 independent approach. however, there are always some portability
214 considerations of some kind, and i have included some options
215 for varying numbers of register variables.
216 perhaps some will still regard the result as a mess!
217
218 1) i assume everything is byte addressable, although i don't actually
219 depend on the byte order, and that bytes are 8 bits.
220 i assume word pointers can be freely cast to and from char pointers.
221 note that 99% of C programs make these assumptions.
222 i always use unsigned char's if the high bit could be set.
223 2) the typedef ``word`` means a 32 bit unsigned integral type.
224 if ``unsigned long`` is not 32 bits, change the typedef in desCore.h.
225 i assume sizeof(word) == 4 EVERYWHERE.
226
227 the (worst-case) cost of my NOT doing endedness-specific optimizations
228 in the data loading and storing code surrounding the key iterations
229 is less than 12%. also, there is the added benefit that
230 the input and output work areas do not need to be word-aligned.
231
232
233 OPTIONAL performance optimizations
234 ==================================
235
236 1) you should define one of ``i386,`` ``vax,`` ``mc68000,`` or ``sparc,``
237 whichever one is closest to the capabilities of your machine.
238 see the start of desCode.h to see exactly what this selection implies.
239 note that if you select the wrong one, the des code will still work;
240 these are just performance tweaks.
241 2) for those with functional ``asm`` keywords: you should change the
242 ROR and ROL macros to use machine rotate instructions if you have them.
243 this will save 2 instructions and a temporary per use,
244 or about 32 to 40 instructions per en/decryption.
245
246 note that gcc is smart enough to translate the ROL/R macros into
247 machine rotates!
248
249 these optimizations are all rather persnickety, yet with them you should
250 be able to get performance equal to assembly-coding, except that:
251
252 1) with the lack of a bit rotate operator in C, rotates have to be synthesized
253 from shifts. so access to ``asm`` will speed things up if your machine
254 has rotates, as explained above in (3) (not necessary if you use gcc).
255 2) if your machine has less than 12 32-bit registers i doubt your compiler will
256 generate good code.
257
258 ``i386`` tries to configure the code for a 386 by only declaring 3 registers
259 (it appears that gcc can use ebx, esi and edi to hold register variables).
260 however, if you like assembly coding, the 386 does have 7 32-bit registers,
261 and if you use ALL of them, use ``scaled by 8`` address modes with displacement
262 and other tricks, you can get reasonable routines for DesQuickCore... with
263 about 250 instructions apiece. For DesSmall... it will help to rearrange
264 des_keymap, i.e., now the sbox # is the high part of the index and
265 the 6 bits of data is the low part; it helps to exchange these.
266
267 since i have no way to conveniently test it i have not provided my
268 shoehorned 386 version. note that with this release of desCore, gcc is able
269 to put everything in registers(!), and generate about 370 instructions apiece
270 for the DesQuickCore... routines!
271
272 coding notes
273 ============
274
275 the en/decryption routines each use 6 necessary register variables,
276 with 4 being actively used at once during the inner iterations.
277 if you don't have 4 register variables get a new machine.
278 up to 8 more registers are used to hold constants in some configurations.
279
280 i assume that the use of a constant is more expensive than using a register:
281
282 a) additionally, i have tried to put the larger constants in registers.
283 registering priority was by the following:
284
285 - anything more than 12 bits (bad for RISC and CISC)
286 - greater than 127 in value (can't use movq or byte immediate on CISC)
287 - 9-127 (may not be able to use CISC shift immediate or add/sub quick),
288 - 1-8 were never registered, being the cheapest constants.
289
290 b) the compiler may be too stupid to realize table and table+256 should
291 be assigned to different constant registers and instead repetitively
292 do the arithmetic, so i assign these to explicit ``m`` register variables
293 when possible and helpful.
294
295 i assume that indexing is cheaper or equivalent to auto increment/decrement,
296 where the index is 7 bits unsigned or smaller.
297 this assumption is reversed for 68k and vax.
298
299 i assume that addresses can be cheaply formed from two registers,
300 or from a register and a small constant.
301 for the 68000, the ``two registers and small offset`` form is used sparingly.
302 all index scaling is done explicitly - no hidden shifts by log2(sizeof).
303
304 the code is written so that even a dumb compiler
305 should never need more than one hidden temporary,
306 increasing the chance that everything will fit in the registers.
307 KEEP THIS MORE SUBTLE POINT IN MIND IF YOU REWRITE ANYTHING.
308
309 (actually, there are some code fragments now which do require two temps,
310 but fixing it would either break the structure of the macros or
311 require declaring another temporary).
312
313
314 special efficient data format
315 ==============================
316
317 bits are manipulated in this arrangement most of the time (S7 S5 S3 S1)::
318
319 003130292827xxxx242322212019xxxx161514131211xxxx080706050403xxxx
320
321 (the x bits are still there, i'm just emphasizing where the S boxes are).
322 bits are rotated left 4 when computing S6 S4 S2 S0::
323
324 282726252423xxxx201918171615xxxx121110090807xxxx040302010031xxxx
325
326 the rightmost two bits are usually cleared so the lower byte can be used
327 as an index into an sbox mapping table. the next two x'd bits are set
328 to various values to access different parts of the tables.
329
330
331 how to use the routines
332
333 datatypes:
334 pointer to 8 byte area of type DesData
335 used to hold keys and input/output blocks to des.
336
337 pointer to 128 byte area of type DesKeys
338 used to hold full 768-bit key.
339 must be long-aligned.
340
341 DesQuickInit()
342 call this before using any other routine with ``Quick`` in its name.
343 it generates the special 64k table these routines need.
344 DesQuickDone()
345 frees this table
346
347 DesMethod(m, k)
348 m points to a 128byte block, k points to an 8 byte des key
349 which must have odd parity (or -1 is returned) and which must
350 not be a (semi-)weak key (or -2 is returned).
351 normally DesMethod() returns 0.
352
353 m is filled in from k so that when one of the routines below
354 is called with m, the routine will act like standard des
355 en/decryption with the key k. if you use DesMethod,
356 you supply a standard 56bit key; however, if you fill in
357 m yourself, you will get a 768bit key - but then it won't
358 be standard. it's 768bits not 1024 because the least significant
359 two bits of each byte are not used. note that these two bits
360 will be set to magic constants which speed up the encryption/decryption
361 on some machines. and yes, each byte controls
362 a specific sbox during a specific iteration.
363
364 you really shouldn't use the 768bit format directly; i should
365 provide a routine that converts 128 6-bit bytes (specified in
366 S-box mapping order or something) into the right format for you.
367 this would entail some byte concatenation and rotation.
368
369 Des{Small|Quick}{Fips|Core}{Encrypt|Decrypt}(d, m, s)
370 performs des on the 8 bytes at s into the 8 bytes at
371 ``d. (d,s: char *)``.
372
373 uses m as a 768bit key as explained above.
374
375 the Encrypt|Decrypt choice is obvious.
376
377 Fips|Core determines whether a completely standard FIPS initial
378 and final permutation is done; if not, then the data is loaded
379 and stored in a nonstandard bit order (FIPS w/o IP/FP).
380
381 Fips slows down Quick by 10%, Small by 9%.
382
383 Small|Quick determines whether you use the normal routine
384 or the crazy quick one which gobbles up 64k more of memory.
385 Small is 50% slower then Quick, but Quick needs 32 times as much
386 memory. Quick is included for programs that do nothing but DES,
387 e.g., encryption filters, etc.
388
389
390 Getting it to compile on your machine
391 =====================================
392
393 there are no machine-dependencies in the code (see porting),
394 except perhaps the ``now()`` macro in desTest.c.
395 ALL generated tables are machine independent.
396 you should edit the Makefile with the appropriate optimization flags
397 for your compiler (MAX optimization).
398
399
400 Speeding up kerberos (and/or its des library)
401 =============================================
402
403 note that i have included a kerberos-compatible interface in desUtil.c
404 through the functions des_key_sched() and des_ecb_encrypt().
405 to use these with kerberos or kerberos-compatible code put desCore.a
406 ahead of the kerberos-compatible library on your linker's command line.
407 you should not need to #include desCore.h; just include the header
408 file provided with the kerberos library.
409
410 Other uses
411 ==========
412
413 the macros in desCode.h would be very useful for putting inline des
414 functions in more complicated encryption routines.
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