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diff --git a/Documentation/crypto/descore-readme.rst b/Documentation/crypto/descore-readme.rst new file mode 100644 index 000000000..45bd9c8ba --- /dev/null +++ b/Documentation/crypto/descore-readme.rst @@ -0,0 +1,414 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. include:: <isonum.txt> + +=========================================== +Fast & Portable DES encryption & decryption +=========================================== + +.. note:: + + Below is the original README file from the descore.shar package, + converted to ReST format. + +------------------------------------------------------------------------------ + +des - fast & portable DES encryption & decryption. + +Copyright |copy| 1992 Dana L. How + +This program is free software; you can redistribute it and/or modify +it under the terms of the GNU Library General Public License as published by +the Free Software Foundation; either version 2 of the License, or +(at your option) any later version. + +This program is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +GNU Library General Public License for more details. + +You should have received a copy of the GNU Library General Public License +along with this program; if not, write to the Free Software +Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + +Author's address: how@isl.stanford.edu + +.. README,v 1.15 1992/05/20 00:25:32 how E + +==>> To compile after untarring/unsharring, just ``make`` <<== + +This package was designed with the following goals: + +1. Highest possible encryption/decryption PERFORMANCE. +2. PORTABILITY to any byte-addressable host with a 32bit unsigned C type +3. Plug-compatible replacement for KERBEROS's low-level routines. + +This second release includes a number of performance enhancements for +register-starved machines. My discussions with Richard Outerbridge, +71755.204@compuserve.com, sparked a number of these enhancements. + +To more rapidly understand the code in this package, inspect desSmallFips.i +(created by typing ``make``) BEFORE you tackle desCode.h. The latter is set +up in a parameterized fashion so it can easily be modified by speed-daemon +hackers in pursuit of that last microsecond. You will find it more +illuminating to inspect one specific implementation, +and then move on to the common abstract skeleton with this one in mind. + + +performance comparison to other available des code which i could +compile on a SPARCStation 1 (cc -O4, gcc -O2): + +this code (byte-order independent): + + - 30us per encryption (options: 64k tables, no IP/FP) + - 33us per encryption (options: 64k tables, FIPS standard bit ordering) + - 45us per encryption (options: 2k tables, no IP/FP) + - 48us per encryption (options: 2k tables, FIPS standard bit ordering) + - 275us to set a new key (uses 1k of key tables) + + this has the quickest encryption/decryption routines i've seen. + since i was interested in fast des filters rather than crypt(3) + and password cracking, i haven't really bothered yet to speed up + the key setting routine. also, i have no interest in re-implementing + all the other junk in the mit kerberos des library, so i've just + provided my routines with little stub interfaces so they can be + used as drop-in replacements with mit's code or any of the mit- + compatible packages below. (note that the first two timings above + are highly variable because of cache effects). + +kerberos des replacement from australia (version 1.95): + + - 53us per encryption (uses 2k of tables) + - 96us to set a new key (uses 2.25k of key tables) + + so despite the author's inclusion of some of the performance + improvements i had suggested to him, this package's + encryption/decryption is still slower on the sparc and 68000. + more specifically, 19-40% slower on the 68020 and 11-35% slower + on the sparc, depending on the compiler; + in full gory detail (ALT_ECB is a libdes variant): + + =============== ============== =============== ================= + compiler machine desCore libdes ALT_ECB slower by + =============== ============== =============== ================= + gcc 2.1 -O2 Sun 3/110 304 uS 369.5uS 461.8uS 22% + cc -O1 Sun 3/110 336 uS 436.6uS 399.3uS 19% + cc -O2 Sun 3/110 360 uS 532.4uS 505.1uS 40% + cc -O4 Sun 3/110 365 uS 532.3uS 505.3uS 38% + gcc 2.1 -O2 Sun 4/50 48 uS 53.4uS 57.5uS 11% + cc -O2 Sun 4/50 48 uS 64.6uS 64.7uS 35% + cc -O4 Sun 4/50 48 uS 64.7uS 64.9uS 35% + =============== ============== =============== ================= + + (my time measurements are not as accurate as his). + + the comments in my first release of desCore on version 1.92: + + - 68us per encryption (uses 2k of tables) + - 96us to set a new key (uses 2.25k of key tables) + + this is a very nice package which implements the most important + of the optimizations which i did in my encryption routines. + it's a bit weak on common low-level optimizations which is why + it's 39%-106% slower. because he was interested in fast crypt(3) and + password-cracking applications, he also used the same ideas to + speed up the key-setting routines with impressive results. + (at some point i may do the same in my package). he also implements + the rest of the mit des library. + + (code from eay@psych.psy.uq.oz.au via comp.sources.misc) + +fast crypt(3) package from denmark: + + the des routine here is buried inside a loop to do the + crypt function and i didn't feel like ripping it out and measuring + performance. his code takes 26 sparc instructions to compute one + des iteration; above, Quick (64k) takes 21 and Small (2k) takes 37. + he claims to use 280k of tables but the iteration calculation seems + to use only 128k. his tables and code are machine independent. + + (code from glad@daimi.aau.dk via alt.sources or comp.sources.misc) + +swedish reimplementation of Kerberos des library + + - 108us per encryption (uses 34k worth of tables) + - 134us to set a new key (uses 32k of key tables to get this speed!) + + the tables used seem to be machine-independent; + he seems to have included a lot of special case code + so that, e.g., ``long`` loads can be used instead of 4 ``char`` loads + when the machine's architecture allows it. + + (code obtained from chalmers.se:pub/des) + +crack 3.3c package from england: + + as in crypt above, the des routine is buried in a loop. it's + also very modified for crypt. his iteration code uses 16k + of tables and appears to be slow. + + (code obtained from aem@aber.ac.uk via alt.sources or comp.sources.misc) + +``highly optimized`` and tweaked Kerberos/Athena code (byte-order dependent): + + - 165us per encryption (uses 6k worth of tables) + - 478us to set a new key (uses <1k of key tables) + + so despite the comments in this code, it was possible to get + faster code AND smaller tables, as well as making the tables + machine-independent. + (code obtained from prep.ai.mit.edu) + +UC Berkeley code (depends on machine-endedness): + - 226us per encryption + - 10848us to set a new key + + table sizes are unclear, but they don't look very small + (code obtained from wuarchive.wustl.edu) + + +motivation and history +====================== + +a while ago i wanted some des routines and the routines documented on sun's +man pages either didn't exist or dumped core. i had heard of kerberos, +and knew that it used des, so i figured i'd use its routines. but once +i got it and looked at the code, it really set off a lot of pet peeves - +it was too convoluted, the code had been written without taking +advantage of the regular structure of operations such as IP, E, and FP +(i.e. the author didn't sit down and think before coding), +it was excessively slow, the author had attempted to clarify the code +by adding MORE statements to make the data movement more ``consistent`` +instead of simplifying his implementation and cutting down on all data +movement (in particular, his use of L1, R1, L2, R2), and it was full of +idiotic ``tweaks`` for particular machines which failed to deliver significant +speedups but which did obfuscate everything. so i took the test data +from his verification program and rewrote everything else. + +a while later i ran across the great crypt(3) package mentioned above. +the fact that this guy was computing 2 sboxes per table lookup rather +than one (and using a MUCH larger table in the process) emboldened me to +do the same - it was a trivial change from which i had been scared away +by the larger table size. in his case he didn't realize you don't need to keep +the working data in TWO forms, one for easy use of half the sboxes in +indexing, the other for easy use of the other half; instead you can keep +it in the form for the first half and use a simple rotate to get the other +half. this means i have (almost) half the data manipulation and half +the table size. in fairness though he might be encoding something particular +to crypt(3) in his tables - i didn't check. + +i'm glad that i implemented it the way i did, because this C version is +portable (the ifdef's are performance enhancements) and it is faster +than versions hand-written in assembly for the sparc! + + +porting notes +============= + +one thing i did not want to do was write an enormous mess +which depended on endedness and other machine quirks, +and which necessarily produced different code and different lookup tables +for different machines. see the kerberos code for an example +of what i didn't want to do; all their endedness-specific ``optimizations`` +obfuscate the code and in the end were slower than a simpler machine +independent approach. however, there are always some portability +considerations of some kind, and i have included some options +for varying numbers of register variables. +perhaps some will still regard the result as a mess! + +1) i assume everything is byte addressable, although i don't actually + depend on the byte order, and that bytes are 8 bits. + i assume word pointers can be freely cast to and from char pointers. + note that 99% of C programs make these assumptions. + i always use unsigned char's if the high bit could be set. +2) the typedef ``word`` means a 32 bit unsigned integral type. + if ``unsigned long`` is not 32 bits, change the typedef in desCore.h. + i assume sizeof(word) == 4 EVERYWHERE. + +the (worst-case) cost of my NOT doing endedness-specific optimizations +in the data loading and storing code surrounding the key iterations +is less than 12%. also, there is the added benefit that +the input and output work areas do not need to be word-aligned. + + +OPTIONAL performance optimizations +================================== + +1) you should define one of ``i386,`` ``vax,`` ``mc68000,`` or ``sparc,`` + whichever one is closest to the capabilities of your machine. + see the start of desCode.h to see exactly what this selection implies. + note that if you select the wrong one, the des code will still work; + these are just performance tweaks. +2) for those with functional ``asm`` keywords: you should change the + ROR and ROL macros to use machine rotate instructions if you have them. + this will save 2 instructions and a temporary per use, + or about 32 to 40 instructions per en/decryption. + + note that gcc is smart enough to translate the ROL/R macros into + machine rotates! + +these optimizations are all rather persnickety, yet with them you should +be able to get performance equal to assembly-coding, except that: + +1) with the lack of a bit rotate operator in C, rotates have to be synthesized + from shifts. so access to ``asm`` will speed things up if your machine + has rotates, as explained above in (3) (not necessary if you use gcc). +2) if your machine has less than 12 32-bit registers i doubt your compiler will + generate good code. + + ``i386`` tries to configure the code for a 386 by only declaring 3 registers + (it appears that gcc can use ebx, esi and edi to hold register variables). + however, if you like assembly coding, the 386 does have 7 32-bit registers, + and if you use ALL of them, use ``scaled by 8`` address modes with displacement + and other tricks, you can get reasonable routines for DesQuickCore... with + about 250 instructions apiece. For DesSmall... it will help to rearrange + des_keymap, i.e., now the sbox # is the high part of the index and + the 6 bits of data is the low part; it helps to exchange these. + + since i have no way to conveniently test it i have not provided my + shoehorned 386 version. note that with this release of desCore, gcc is able + to put everything in registers(!), and generate about 370 instructions apiece + for the DesQuickCore... routines! + +coding notes +============ + +the en/decryption routines each use 6 necessary register variables, +with 4 being actively used at once during the inner iterations. +if you don't have 4 register variables get a new machine. +up to 8 more registers are used to hold constants in some configurations. + +i assume that the use of a constant is more expensive than using a register: + +a) additionally, i have tried to put the larger constants in registers. + registering priority was by the following: + + - anything more than 12 bits (bad for RISC and CISC) + - greater than 127 in value (can't use movq or byte immediate on CISC) + - 9-127 (may not be able to use CISC shift immediate or add/sub quick), + - 1-8 were never registered, being the cheapest constants. + +b) the compiler may be too stupid to realize table and table+256 should + be assigned to different constant registers and instead repetitively + do the arithmetic, so i assign these to explicit ``m`` register variables + when possible and helpful. + +i assume that indexing is cheaper or equivalent to auto increment/decrement, +where the index is 7 bits unsigned or smaller. +this assumption is reversed for 68k and vax. + +i assume that addresses can be cheaply formed from two registers, +or from a register and a small constant. +for the 68000, the ``two registers and small offset`` form is used sparingly. +all index scaling is done explicitly - no hidden shifts by log2(sizeof). + +the code is written so that even a dumb compiler +should never need more than one hidden temporary, +increasing the chance that everything will fit in the registers. +KEEP THIS MORE SUBTLE POINT IN MIND IF YOU REWRITE ANYTHING. + +(actually, there are some code fragments now which do require two temps, +but fixing it would either break the structure of the macros or +require declaring another temporary). + + +special efficient data format +============================== + +bits are manipulated in this arrangement most of the time (S7 S5 S3 S1):: + + 003130292827xxxx242322212019xxxx161514131211xxxx080706050403xxxx + +(the x bits are still there, i'm just emphasizing where the S boxes are). +bits are rotated left 4 when computing S6 S4 S2 S0:: + + 282726252423xxxx201918171615xxxx121110090807xxxx040302010031xxxx + +the rightmost two bits are usually cleared so the lower byte can be used +as an index into an sbox mapping table. the next two x'd bits are set +to various values to access different parts of the tables. + + +how to use the routines + +datatypes: + pointer to 8 byte area of type DesData + used to hold keys and input/output blocks to des. + + pointer to 128 byte area of type DesKeys + used to hold full 768-bit key. + must be long-aligned. + +DesQuickInit() + call this before using any other routine with ``Quick`` in its name. + it generates the special 64k table these routines need. +DesQuickDone() + frees this table + +DesMethod(m, k) + m points to a 128byte block, k points to an 8 byte des key + which must have odd parity (or -1 is returned) and which must + not be a (semi-)weak key (or -2 is returned). + normally DesMethod() returns 0. + + m is filled in from k so that when one of the routines below + is called with m, the routine will act like standard des + en/decryption with the key k. if you use DesMethod, + you supply a standard 56bit key; however, if you fill in + m yourself, you will get a 768bit key - but then it won't + be standard. it's 768bits not 1024 because the least significant + two bits of each byte are not used. note that these two bits + will be set to magic constants which speed up the encryption/decryption + on some machines. and yes, each byte controls + a specific sbox during a specific iteration. + + you really shouldn't use the 768bit format directly; i should + provide a routine that converts 128 6-bit bytes (specified in + S-box mapping order or something) into the right format for you. + this would entail some byte concatenation and rotation. + +Des{Small|Quick}{Fips|Core}{Encrypt|Decrypt}(d, m, s) + performs des on the 8 bytes at s into the 8 bytes at + ``d. (d,s: char *)``. + + uses m as a 768bit key as explained above. + + the Encrypt|Decrypt choice is obvious. + + Fips|Core determines whether a completely standard FIPS initial + and final permutation is done; if not, then the data is loaded + and stored in a nonstandard bit order (FIPS w/o IP/FP). + + Fips slows down Quick by 10%, Small by 9%. + + Small|Quick determines whether you use the normal routine + or the crazy quick one which gobbles up 64k more of memory. + Small is 50% slower then Quick, but Quick needs 32 times as much + memory. Quick is included for programs that do nothing but DES, + e.g., encryption filters, etc. + + +Getting it to compile on your machine +===================================== + +there are no machine-dependencies in the code (see porting), +except perhaps the ``now()`` macro in desTest.c. +ALL generated tables are machine independent. +you should edit the Makefile with the appropriate optimization flags +for your compiler (MAX optimization). + + +Speeding up kerberos (and/or its des library) +============================================= + +note that i have included a kerberos-compatible interface in desUtil.c +through the functions des_key_sched() and des_ecb_encrypt(). +to use these with kerberos or kerberos-compatible code put desCore.a +ahead of the kerberos-compatible library on your linker's command line. +you should not need to #include desCore.h; just include the header +file provided with the kerberos library. + +Other uses +========== + +the macros in desCode.h would be very useful for putting inline des +functions in more complicated encryption routines. |