rc2.c   [plain text]

/**********************************************************************\ 
* 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> 

#include <CommonCrypto/rc2.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( RC2_Schedule *key_schedule, 
                      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(&key_schedule->xkey, key, len); 
        /* Phase 1: Expand input key to 128 bytes */ 
        if (len < 128) { 
                i = 0; 
                x = ((unsigned char *)key_schedule->xkey)[len-1]; 
                do { 
                        x = permute[(x + ((unsigned char *)key_schedule->xkey)[i++]) & 255]; 
                        ((unsigned char *)key_schedule->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 *)key_schedule->xkey)[i] & (255 >> (7 & -bits))]; 
        ((unsigned char *)key_schedule->xkey)[i] = x; 
        while (i--) { 
                x = permute[ x ^ ((unsigned char *)key_schedule->xkey)[i+len] ]; 
                ((unsigned char *)key_schedule->xkey)[i] = x; 
        } 
        /* Phase 3 - copy to xkey in little-endian order */ 
        i = 63; 
        do { 
                key_schedule->xkey[i] =  ((unsigned char *)key_schedule->xkey)[2*i] + 
                          (((unsigned char *)key_schedule->xkey)[2*i+1] << 8); 
        } while (i--); 
        } 
/**********************************************************************\ 
* Encrypt an 8-byte block of plaintext using the given key.            * 
\**********************************************************************/ 
void rc2_encrypt( const RC2_Schedule *key_schedule, 
                  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) + key_schedule->xkey[4*i+0]; 
                x10 = (x10 << 1) + (x10 >> 15 & 1); 
                x32 += (x54 & ~x10) + (x76 & x10) + key_schedule->xkey[4*i+1]; 
                x32 = (x32 << 2) + (x32 >> 14 & 3); 
                x54 += (x76 & ~x32) + (x10 & x32) + key_schedule->xkey[4*i+2]; 
                x54 = (x54 << 3) + (x54 >> 13 & 7); 
                x76 += (x10 & ~x54) + (x32 & x54) + key_schedule->xkey[4*i+3]; 
                x76 = (x76 << 5) + (x76 >> 11 & 31); 
                if (i == 4 || i == 10) { 
                        x10 += key_schedule->xkey[x76 & 63]; 
                        x32 += key_schedule->xkey[x10 & 63]; 
                        x54 += key_schedule->xkey[x32 & 63]; 
                        x76 += key_schedule->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 RC2_Schedule *key_schedule, 
                  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) + key_schedule->xkey[4*i+3]; 
                x54 &= 65535; 
                x54 = (x54 << 13) + (x54 >> 3); 
                x54 -= (x76 & ~x32) + (x10 & x32) + key_schedule->xkey[4*i+2]; 
                x32 &= 65535; 
                x32 = (x32 << 14) + (x32 >> 2); 
                x32 -= (x54 & ~x10) + (x76 & x10) + key_schedule->xkey[4*i+1]; 
                x10 &= 65535; 
                x10 = (x10 << 15) + (x10 >> 1); 
                x10 -= (x32 & ~x76) + (x54 & x76) + key_schedule->xkey[4*i+0]; 
                if (i == 5 || i == 11) { 
                        x76 -= key_schedule->xkey[x54 & 63]; 
                        x54 -= key_schedule->xkey[x32 & 63]; 
                        x32 -= key_schedule->xkey[x10 & 63]; 
                        x10 -= key_schedule->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); 
        }