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