Reposted from sci.crypt: /**********************************************************************\ * 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); }