/*
    SKIP32 -- 32 bit block cipher based on SKIPJACK.
    Written by Greg Rose, QUALCOMM Australia, 1999/04/27.

    In common: F-table, G-permutation, key schedule.
    Different: 24 round feistel structure.
    Based on:  Unoptimized test implementation of SKIPJACK algorithm
               Panu Rissanen <bande@lut.fi>

    SKIPJACK and KEA Algorithm Specifications
    Version 2.0
    29 May 1998

    Not copyright, no rights reserved.
 */

#include "skip32.h"

typedef unsigned char   BYTE; /* 8 bits */
typedef unsigned short  WORD; /* 16 bits */

static const BYTE ftable[256] = {
 0xa3,0xd7,0x09,0x83,0xf8,0x48,0xf6,0xf4,0xb3,0x21,0x15,0x78,0x99,0xb1,0xaf,0xf9,
 0xe7,0x2d,0x4d,0x8a,0xce,0x4c,0xca,0x2e,0x52,0x95,0xd9,0x1e,0x4e,0x38,0x44,0x28,
 0x0a,0xdf,0x02,0xa0,0x17,0xf1,0x60,0x68,0x12,0xb7,0x7a,0xc3,0xe9,0xfa,0x3d,0x53,
 0x96,0x84,0x6b,0xba,0xf2,0x63,0x9a,0x19,0x7c,0xae,0xe5,0xf5,0xf7,0x16,0x6a,0xa2,
 0x39,0xb6,0x7b,0x0f,0xc1,0x93,0x81,0x1b,0xee,0xb4,0x1a,0xea,0xd0,0x91,0x2f,0xb8,
 0x55,0xb9,0xda,0x85,0x3f,0x41,0xbf,0xe0,0x5a,0x58,0x80,0x5f,0x66,0x0b,0xd8,0x90,
 0x35,0xd5,0xc0,0xa7,0x33,0x06,0x65,0x69,0x45,0x00,0x94,0x56,0x6d,0x98,0x9b,0x76,
 0x97,0xfc,0xb2,0xc2,0xb0,0xfe,0xdb,0x20,0xe1,0xeb,0xd6,0xe4,0xdd,0x47,0x4a,0x1d,
 0x42,0xed,0x9e,0x6e,0x49,0x3c,0xcd,0x43,0x27,0xd2,0x07,0xd4,0xde,0xc7,0x67,0x18,
 0x89,0xcb,0x30,0x1f,0x8d,0xc6,0x8f,0xaa,0xc8,0x74,0xdc,0xc9,0x5d,0x5c,0x31,0xa4,
 0x70,0x88,0x61,0x2c,0x9f,0x0d,0x2b,0x87,0x50,0x82,0x54,0x64,0x26,0x7d,0x03,0x40,
 0x34,0x4b,0x1c,0x73,0xd1,0xc4,0xfd,0x3b,0xcc,0xfb,0x7f,0xab,0xe6,0x3e,0x5b,0xa5,
 0xad,0x04,0x23,0x9c,0x14,0x51,0x22,0xf0,0x29,0x79,0x71,0x7e,0xff,0x8c,0x0e,0xe2,
 0x0c,0xef,0xbc,0x72,0x75,0x6f,0x37,0xa1,0xec,0xd3,0x8e,0x62,0x8b,0x86,0x10,0xe8,
 0x08,0x77,0x11,0xbe,0x92,0x4f,0x24,0xc5,0x32,0x36,0x9d,0xcf,0xf3,0xa6,0xbb,0xac,
 0x5e,0x6c,0xa9,0x13,0x57,0x25,0xb5,0xe3,0xbd,0xa8,0x3a,0x01,0x05,0x59,0x2a,0x46
 };

static WORD
g(BYTE *key, int k, WORD w)
 {
     BYTE g1, g2, g3, g4, g5, g6;

     g1 = (w>>8)&0xff;
     g2 = w&0xff;

     g3 = ftable[g2 ^ key[(4*k)%10]] ^ g1;
     g4 = ftable[g3 ^ key[(4*k+1)%10]] ^ g2;
     g5 = ftable[g4 ^ key[(4*k+2)%10]] ^ g3;
     g6 = ftable[g5 ^ key[(4*k+3)%10]] ^ g4;

     return ((g5<<8) + g6);
 }

void
fpe_skip32(BYTE key[10], BYTE buf[4], int encrypt)
{
    int         k; /* round number */
    int         i; /* round counter */
    int         kstep;
    WORD        wl, wr;

    /* sort out direction */
    if (encrypt)
        kstep = 1, k = 0;
    else
        kstep = -1, k = 23;

    /* pack into words */
    wl = (buf[0] << 8) + buf[1];
    wr = (buf[2] << 8) + buf[3];

    /* 24 feistel rounds, doubled up */
    for (i = 0; i < 24/2; ++i) {
        wr ^= g(key, k, wl) ^ k;
        k += kstep;
        wl ^= g(key, k, wr) ^ k;
        k += kstep;
    }

    /* implicitly swap halves while unpacking */
    buf[0] = wr >> 8;   buf[1] = wr & 0xFF;
    buf[2] = wl >> 8;   buf[3] = wl & 0xFF;
}