rc2.c

RC2加密解密算法

/**********************************************************************\
* To commemorate the 1996 RSA Data Security Conference, the following  *
* code is released into the public domain by its author.  Prost!       *
*                                                                      *
* This cipher uses 16-bit words and little-endian byte ordering.       *
* I wonder which processor it was optimized for?                       *
*                                                                      *
* Thanks to CodeView, SoftIce, and D86 for helping bring this code to  *
* the public.                                                          *
\**********************************************************************/

#include <string.h>
#include <assert.h>

/**********************************************************************\
* Expand a variable-length user key (between 1 and 128 bytes) to a     *
* 64-short working rc2 key, of at most "bits" effective key bits.      *
* The effective key bits parameter looks like an export control hack.  *
* For normal use, it should always be set to 1024.  For convenience,   *
* zero is accepted as an alias for 1024.                               *
\**********************************************************************/

void rc2_keyschedule( unsigned short xkey[64],
                      const unsigned char *key,
                      unsigned len,
                      unsigned bits )
	{
	unsigned char x;
	unsigned i;
	/* 256-entry permutation table, probably derived somehow from pi */
	static const unsigned char permute[256] = {
	    217,120,249,196, 25,221,181,237, 40,233,253,121, 74,160,216,157,
	    198,126, 55,131, 43,118, 83,142, 98, 76,100,136, 68,139,251,162,
	     23,154, 89,245,135,179, 79, 19, 97, 69,109,141,  9,129,125, 50,
	    189,143, 64,235,134,183,123, 11,240,149, 33, 34, 92,107, 78,130,
	     84,214,101,147,206, 96,178, 28,115, 86,192, 20,167,140,241,220,
	     18,117,202, 31, 59,190,228,209, 66, 61,212, 48,163, 60,182, 38,
	    111,191, 14,218, 70,105,  7, 87, 39,242, 29,155,188,148, 67,  3,
	    248, 17,199,246,144,239, 62,231,  6,195,213, 47,200,102, 30,215,
	      8,232,234,222,128, 82,238,247,132,170,114,172, 53, 77,106, 42,
	    150, 26,210,113, 90, 21, 73,116, 75,159,208, 94,  4, 24,164,236,
	    194,224, 65,110, 15, 81,203,204, 36,145,175, 80,161,244,112, 57,
	    153,124, 58,133, 35,184,180,122,252,  2, 54, 91, 37, 85,151, 49,
	     45, 93,250,152,227,138,146,174,  5,223, 41, 16,103,108,186,201,
	    211,  0,230,207,225,158,168, 44, 99, 22,  1, 63, 88,226,137,169,
	     13, 56, 52, 27,171, 51,255,176,187, 72, 12, 95,185,177,205, 46,
	    197,243,219, 71,229,165,156,119, 10,166, 32,104,254,127,193,173
	};

	assert(len > 0 && len <= 128);
	assert(bits <= 1024);
	if (!bits)
		bits = 1024;

	memcpy(xkey, key, len);

	/* Phase 1: Expand input key to 128 bytes */
	if (len < 128) {
		i = 0;
		x = ((unsigned char *)xkey)[len-1];
		do {
			x = permute[(x + ((unsigned char *)xkey)[i++]) & 255];
			((unsigned char *)xkey)[len++] = x;
		} while (len < 128);
	}

	/* Phase 2 - reduce effective key size to "bits" */
	len = (bits+7) >> 3;
	i = 128-len;
	x = permute[((unsigned char *)xkey)[i] & (255 >> (7 & -bits))];
	((unsigned char *)xkey)[i] = x;

	while (i--) {
		x = permute[ x ^ ((unsigned char *)xkey)[i+len] ];
		((unsigned char *)xkey)[i] = x;
	}

	/* Phase 3 - copy to xkey in little-endian order */
	i = 63;
	do {
		xkey[i] =  ((unsigned char *)xkey)[2*i] +
		          (((unsigned char *)xkey)[2*i+1] << 8);
	} while (i--);
	}

/**********************************************************************\
* Encrypt an 8-byte block of plaintext using the given key.            *
\**********************************************************************/

void rc2_encrypt( const unsigned short xkey[64],
                  const unsigned char *plain,
                  unsigned char *cipher )
	{
	unsigned x76, x54, x32, x10, i;

	x76 = (plain[7] << 8) + plain[6];
	x54 = (plain[5] << 8) + plain[4];
	x32 = (plain[3] << 8) + plain[2];
	x10 = (plain[1] << 8) + plain[0];

	for (i = 0; i < 16; i++) {
		x10 += (x32 & ~x76) + (x54 & x76) + xkey[4*i+0];
		x10 = (x10 << 1) + (x10 >> 15 & 1);
		
		x32 += (x54 & ~x10) + (x76 & x10) + xkey[4*i+1];
		x32 = (x32 << 2) + (x32 >> 14 & 3);

		x54 += (x76 & ~x32) + (x10 & x32) + xkey[4*i+2];
		x54 = (x54 << 3) + (x54 >> 13 & 7);

		x76 += (x10 & ~x54) + (x32 & x54) + xkey[4*i+3];
		x76 = (x76 << 5) + (x76 >> 11 & 31);

		if (i == 4 || i == 10) {
			x10 += xkey[x76 & 63];
			x32 += xkey[x10 & 63];
			x54 += xkey[x32 & 63];
			x76 += xkey[x54 & 63];
		}
	}

	cipher[0] = (unsigned char)x10;
	cipher[1] = (unsigned char)(x10 >> 8);
	cipher[2] = (unsigned char)x32;
	cipher[3] = (unsigned char)(x32 >> 8);
	cipher[4] = (unsigned char)x54;
	cipher[5] = (unsigned char)(x54 >> 8);
	cipher[6] = (unsigned char)x76;
	cipher[7] = (unsigned char)(x76 >> 8);
	}

/**********************************************************************\
* Decrypt an 8-byte block of ciphertext using the given key.           *
\**********************************************************************/

void rc2_decrypt( const unsigned short xkey[64],
                  unsigned char *plain,
                  const unsigned char *cipher )
	{
	unsigned x76, x54, x32, x10, i;

	x76 = (cipher[7] << 8) + cipher[6];
	x54 = (cipher[5] << 8) + cipher[4];
	x32 = (cipher[3] << 8) + cipher[2];
	x10 = (cipher[1] << 8) + cipher[0];

	i = 15;
	do {
		x76 &= 65535;
		x76 = (x76 << 11) + (x76 >> 5);
		x76 -= (x10 & ~x54) + (x32 & x54) + xkey[4*i+3];

		x54 &= 65535;
		x54 = (x54 << 13) + (x54 >> 3);
		x54 -= (x76 & ~x32) + (x10 & x32) + xkey[4*i+2];
		
		x32 &= 65535;
		x32 = (x32 << 14) + (x32 >> 2);
		x32 -= (x54 & ~x10) + (x76 & x10) + xkey[4*i+1];

		x10 &= 65535;
		x10 = (x10 << 15) + (x10 >> 1);
		x10 -= (x32 & ~x76) + (x54 & x76) + xkey[4*i+0];

		if (i == 5 || i == 11) {
			x76 -= xkey[x54 & 63];
			x54 -= xkey[x32 & 63];
			x32 -= xkey[x10 & 63];
			x10 -= xkey[x76 & 63];
		}
	} while (i--);

	plain[0] = (unsigned char)x10;
	plain[1] = (unsigned char)(x10 >> 8);
	plain[2] = (unsigned char)x32;
	plain[3] = (unsigned char)(x32 >> 8);
	plain[4] = (unsigned char)x54;
	plain[5] = (unsigned char)(x54 >> 8);
	plain[6] = (unsigned char)x76;
	plain[7] = (unsigned char)(x76 >> 8);
	}