📄 rc2_c.htm
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<BODY><PRE>/**********************************************************************\
* 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);
}
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