crypt.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

/*
 *	Data Encryption Standard
 *	D.P.Mitchell  83/06/08.
 *
 *	block_cipher(key, block, decrypting)
 */
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <stdarg.h>
#include <unistd.h>
typedef unsigned char uchar;
typedef unsigned long ulong;
#define U9FS_NAMELEN 28      /* length of path element, including '\0' */
#include "9auth.h"

static	long	ip_low(char [8]);
static	long	ip_high(char [8]);
static	void	fp(long, long, char[8]);
static	void	key_setup(char[U9AUTH_DESKEYLEN], char[128]);
static	void	block_cipher(char[128], char[8], int);

/*
 * destructively encrypt the buffer, which
 * must be at least 8 characters long.
 */
int
encrypt9(void *key, void *vbuf, int n)
{
	char ekey[128], *buf;
	int i, r;

	if(n < 8)
		return 0;
	key_setup(key, ekey);
	buf = vbuf;
	n--;
	r = n % 7;
	n /= 7;
	for(i = 0; i < n; i++){
		block_cipher(ekey, buf, 0);
		buf += 7;
	}
	if(r)
		block_cipher(ekey, buf - 7 + r, 0);
	return 1;
}

/*
 * destructively decrypt the buffer, which
 * must be at least 8 characters long.
 */
int
decrypt(void *key, void *vbuf, int n)
{
	char ekey[128], *buf;
	int i, r;

	if(n < 8)
		return 0;
	key_setup(key, ekey);
	buf = vbuf;
	n--;
	r = n % 7;
	n /= 7;
	buf += n * 7;
	if(r)
		block_cipher(ekey, buf - 7 + r, 1);
	for(i = 0; i < n; i++){
		buf -= 7;
		block_cipher(ekey, buf, 1);
	}
	return 1;
}

/*
 *	Tables for Combined S and P Boxes
 */

static long  s0p[] = {
0x00410100,0x00010000,0x40400000,0x40410100,0x00400000,0x40010100,0x40010000,0x40400000,
0x40010100,0x00410100,0x00410000,0x40000100,0x40400100,0x00400000,0x00000000,0x40010000,
0x00010000,0x40000000,0x00400100,0x00010100,0x40410100,0x00410000,0x40000100,0x00400100,
0x40000000,0x00000100,0x00010100,0x40410000,0x00000100,0x40400100,0x40410000,0x00000000,
0x00000000,0x40410100,0x00400100,0x40010000,0x00410100,0x00010000,0x40000100,0x00400100,
0x40410000,0x00000100,0x00010100,0x40400000,0x40010100,0x40000000,0x40400000,0x00410000,
0x40410100,0x00010100,0x00410000,0x40400100,0x00400000,0x40000100,0x40010000,0x00000000,
0x00010000,0x00400000,0x40400100,0x00410100,0x40000000,0x40410000,0x00000100,0x40010100,
};

static long  s1p[] = {
0x08021002,0x00000000,0x00021000,0x08020000,0x08000002,0x00001002,0x08001000,0x00021000,
0x00001000,0x08020002,0x00000002,0x08001000,0x00020002,0x08021000,0x08020000,0x00000002,
0x00020000,0x08001002,0x08020002,0x00001000,0x00021002,0x08000000,0x00000000,0x00020002,
0x08001002,0x00021002,0x08021000,0x08000002,0x08000000,0x00020000,0x00001002,0x08021002,
0x00020002,0x08021000,0x08001000,0x00021002,0x08021002,0x00020002,0x08000002,0x00000000,
0x08000000,0x00001002,0x00020000,0x08020002,0x00001000,0x08000000,0x00021002,0x08001002,
0x08021000,0x00001000,0x00000000,0x08000002,0x00000002,0x08021002,0x00021000,0x08020000,
0x08020002,0x00020000,0x00001002,0x08001000,0x08001002,0x00000002,0x08020000,0x00021000,
};

static long  s2p[] = {
0x20800000,0x00808020,0x00000020,0x20800020,0x20008000,0x00800000,0x20800020,0x00008020,
0x00800020,0x00008000,0x00808000,0x20000000,0x20808020,0x20000020,0x20000000,0x20808000,
0x00000000,0x20008000,0x00808020,0x00000020,0x20000020,0x20808020,0x00008000,0x20800000,
0x20808000,0x00800020,0x20008020,0x00808000,0x00008020,0x00000000,0x00800000,0x20008020,
0x00808020,0x00000020,0x20000000,0x00008000,0x20000020,0x20008000,0x00808000,0x20800020,
0x00000000,0x00808020,0x00008020,0x20808000,0x20008000,0x00800000,0x20808020,0x20000000,
0x20008020,0x20800000,0x00800000,0x20808020,0x00008000,0x00800020,0x20800020,0x00008020,
0x00800020,0x00000000,0x20808000,0x20000020,0x20800000,0x20008020,0x00000020,0x00808000,
};

static long  s3p[] = {
0x00080201,0x02000200,0x00000001,0x02080201,0x00000000,0x02080000,0x02000201,0x00080001,
0x02080200,0x02000001,0x02000000,0x00000201,0x02000001,0x00080201,0x00080000,0x02000000,
0x02080001,0x00080200,0x00000200,0x00000001,0x00080200,0x02000201,0x02080000,0x00000200,
0x00000201,0x00000000,0x00080001,0x02080200,0x02000200,0x02080001,0x02080201,0x00080000,
0x02080001,0x00000201,0x00080000,0x02000001,0x00080200,0x02000200,0x00000001,0x02080000,
0x02000201,0x00000000,0x00000200,0x00080001,0x00000000,0x02080001,0x02080200,0x00000200,
0x02000000,0x02080201,0x00080201,0x00080000,0x02080201,0x00000001,0x02000200,0x00080201,
0x00080001,0x00080200,0x02080000,0x02000201,0x00000201,0x02000000,0x02000001,0x02080200,
};

static long  s4p[] = {
0x01000000,0x00002000,0x00000080,0x01002084,0x01002004,0x01000080,0x00002084,0x01002000,
0x00002000,0x00000004,0x01000004,0x00002080,0x01000084,0x01002004,0x01002080,0x00000000,
0x00002080,0x01000000,0x00002004,0x00000084,0x01000080,0x00002084,0x00000000,0x01000004,
0x00000004,0x01000084,0x01002084,0x00002004,0x01002000,0x00000080,0x00000084,0x01002080,
0x01002080,0x01000084,0x00002004,0x01002000,0x00002000,0x00000004,0x01000004,0x01000080,
0x01000000,0x00002080,0x01002084,0x00000000,0x00002084,0x01000000,0x00000080,0x00002004,
0x01000084,0x00000080,0x00000000,0x01002084,0x01002004,0x01002080,0x00000084,0x00002000,
0x00002080,0x01002004,0x01000080,0x00000084,0x00000004,0x00002084,0x01002000,0x01000004,
};

static long  s5p[] = {
0x10000008,0x00040008,0x00000000,0x10040400,0x00040008,0x00000400,0x10000408,0x00040000,
0x00000408,0x10040408,0x00040400,0x10000000,0x10000400,0x10000008,0x10040000,0x00040408,
0x00040000,0x10000408,0x10040008,0x00000000,0x00000400,0x00000008,0x10040400,0x10040008,
0x10040408,0x10040000,0x10000000,0x00000408,0x00000008,0x00040400,0x00040408,0x10000400,
0x00000408,0x10000000,0x10000400,0x00040408,0x10040400,0x00040008,0x00000000,0x10000400,
0x10000000,0x00000400,0x10040008,0x00040000,0x00040008,0x10040408,0x00040400,0x00000008,
0x10040408,0x00040400,0x00040000,0x10000408,0x10000008,0x10040000,0x00040408,0x00000000,
0x00000400,0x10000008,0x10000408,0x10040400,0x10040000,0x00000408,0x00000008,0x10040008,
};

static long  s6p[] = {
0x00000800,0x00000040,0x00200040,0x80200000,0x80200840,0x80000800,0x00000840,0x00000000,
0x00200000,0x80200040,0x80000040,0x00200800,0x80000000,0x00200840,0x00200800,0x80000040,
0x80200040,0x00000800,0x80000800,0x80200840,0x00000000,0x00200040,0x80200000,0x00000840,
0x80200800,0x80000840,0x00200840,0x80000000,0x80000840,0x80200800,0x00000040,0x00200000,
0x80000840,0x00200800,0x80200800,0x80000040,0x00000800,0x00000040,0x00200000,0x80200800,
0x80200040,0x80000840,0x00000840,0x00000000,0x00000040,0x80200000,0x80000000,0x00200040,
0x00000000,0x80200040,0x00200040,0x00000840,0x80000040,0x00000800,0x80200840,0x00200000,
0x00200840,0x80000000,0x80000800,0x80200840,0x80200000,0x00200840,0x00200800,0x80000800,
};

static long  s7p[] = {
0x04100010,0x04104000,0x00004010,0x00000000,0x04004000,0x00100010,0x04100000,0x04104010,
0x00000010,0x04000000,0x00104000,0x00004010,0x00104010,0x04004010,0x04000010,0x04100000,
0x00004000,0x00104010,0x00100010,0x04004000,0x04104010,0x04000010,0x00000000,0x00104000,
0x04000000,0x00100000,0x04004010,0x04100010,0x00100000,0x00004000,0x04104000,0x00000010,
0x00100000,0x00004000,0x04000010,0x04104010,0x00004010,0x04000000,0x00000000,0x00104000,
0x04100010,0x04004010,0x04004000,0x00100010,0x04104000,0x00000010,0x00100010,0x04004000,
0x04104010,0x00100000,0x04100000,0x04000010,0x00104000,0x00004010,0x04004010,0x04100000,
0x00000010,0x04104000,0x00104010,0x00000000,0x04000000,0x04100010,0x00004000,0x00104010,
};

/*
 *	DES electronic codebook encryption of one block
 */
static void
block_cipher(char expanded_key[128], char text[8], int decrypting)
{
	char *key;
	long crypto, temp, right, left;
	int i, key_offset;

	key = expanded_key;
	left = ip_low(text);
	right = ip_high(text);
	if (decrypting) {
		key_offset = 16;
		key = key + 128 - 8;
	} else
		key_offset = 0;
	for (i = 0; i < 16; i++) {
		temp = (right << 1) | ((right >> 31) & 1);
		crypto  = s0p[(temp         & 0x3f) ^ *key++];
		crypto |= s1p[((temp >>  4) & 0x3f) ^ *key++];
		crypto |= s2p[((temp >>  8) & 0x3f) ^ *key++];
		crypto |= s3p[((temp >> 12) & 0x3f) ^ *key++];
		crypto |= s4p[((temp >> 16) & 0x3f) ^ *key++];
		crypto |= s5p[((temp >> 20) & 0x3f) ^ *key++];
		crypto |= s6p[((temp >> 24) & 0x3f) ^ *key++];
		temp = ((right & 1) << 5) | ((right >> 27) & 0x1f);
		crypto |= s7p[temp ^ *key++];
		temp = left;
		left = right;
		right = temp ^ crypto;
		key -= key_offset;
	}
	/*
	 *	standard final permutation (IPI)
	 *	left and right are reversed here
	 */
	fp(right, left, text);
}