readme.des

DES 加解密算法 C 源码 研究DES算法的朋友值得

Data Encryption Standard routines in portable C and 386/486 assembler
Phil Karn, KA9Q
September 2, 1994

There are two user calls, deskey() for creating a key schedule for
encryption or decryption, and des() that does the actual encryption or
decryption. They are declared as follows:

void
deskey(unsigned long k[16][2],unsigned char key[8],int decrypt);

void
des(unsigned long k[16][2],unsigned char buf[8]);

The deskey() function creates a key schedule 'k' from 'key' for
later use by des(); both arrays must be created by the caller.

The des() function encrypts or decrypts the user-provided buffer 'buf'
in place under control of the key schedule 'k'. Whether des() encrypts
or decrypts is controlled by the 'decrypt' argument to deskey() when
the key schedule is created. This is because DES encryption and
decryption are identical except for the key schedule being in reverse
order.

The deskey() routine is in portable C; if you want great speed (e.g.,
for key searching or UNIX password cracking) you'll have to tune it
yourself.

There are three flavors of the des() routine, one in portable C and
two in 386/486 assembler. One assembler version, desborl.cas, is in
inline assembler format for Borland C++ and can be used in DOS
environments.  The other, desgnu.s, is in GNU 'as' format and is
intended for use in 386 BSD UNIX systems (e.g., BSDI, FreeBSD,
NetBSD). The portable C version is in desport.c.

All three versions of des() refer to an external table containing the
combined S&P boxes. Because the format of this table differs between
the assembler and C versions, different symbol names are used: Spbox
for C and Spboxa for assembler. Both tables are generated as C source
files by the program gensp, which takes one argument: 'a' for
assembler and 'c' for C.

This is an almost complete rewrite of my old public domain DES code
written circa 1987, which in turn borrowed heavily from Jim Gillogly's
1977 public domain code. I pretty much kept my key scheduling code,
but the actual encrypt/decrypt routines are taken from from Richard
Outerbridge's DES code as printed in Schneier's "Applied
Cryptography."

Note to Borland C++ users: Borland C++ 3.1 has no way of ensuring that
32-bit objects (in particular the Spbox[] array) are aligned on a
32-bit boundary. Even the -a option provides only 16-bit alignment. So
without any special precautions it's a 50-50 crapshoot. I've included
a special dessp.asm file which has been manually messaged to ensure
32-bit alignment.  It also helps if callers to des() can ensure that
the key schedule array is 32-bit aligned; this is automatic if the
array is created with malloc().

Some measured execution speeds in crypts/sec:
Borland Assembler version, Borland C++ 3.1 -O2, DOS 16-bit real mode:
110,254 (90 Mhz Pentium)
72,098 (60 Mhz Pentium)
43,460 (486DX-50)

Gnu assembler version, 32-bit protected mode:
69,348 (486DX2-66, BSDI 1.1)

Portable C version:
109,890 (Sparc 20 Model 61, GCC 2.5.8 -O)
93,457 (Sparc 1000)
88,495 (Sparc 5/85)
84,034 (Sparc 2000)
83,333 (Sparc 20 Model 51)
80,000 (Sparc 10 Model 51)
71,942 (Sparc 5/70)
66,666 (Sparc 10 Model 41)
66,225 (Sparc 10 Model 30)
45,248 (Sun 4/15)
44,643 (Sun 4/30)
36,101 (Sun 4/690)
35,335 (Sun 4/75)
35,199 (486DX2-66, BSDI 1.1, GCC 1.42 -O, 32-bit prot mode)
11,561 (486DX-50, DOS, Borland C++ 3.1 -O2, 16-bit real mode)

This code is in the public domain. Bug reports and enhancements are
appreciated.

Phil Karn KA9Q, [e-mail]