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Annotation of truecrypt/crypto/twofish.c, revision 1.1

1.1     ! root        1: /* This is an independent implementation of the encryption algorithm:   */
        !             2: /*                                                                      */
        !             3: /*         Twofish by Bruce Schneier and colleagues                     */
        !             4: /*                                                                      */
        !             5: /* which is a candidate algorithm in the Advanced Encryption Standard   */
        !             6: /* programme of the US National Institute of Standards and Technology.  */
        !             7: /*                                                                      */
        !             8: /* Copyright in this implementation is held by Dr B R Gladman but I     */
        !             9: /* hereby give permission for its free direct or derivative use subject */
        !            10: /* to acknowledgment of its origin and compliance with any conditions   */
        !            11: /* that the originators of the algorithm place on its exploitation.     */
        !            12: /*                                                                      */
        !            13: /* My thanks to Doug Whiting and Niels Ferguson for comments that led   */
        !            14: /* to improvements in this implementation.                              */
        !            15: /*                                                                      */
        !            16: /* Dr Brian Gladman ([email protected]) 14th January 1999     */
        !            17: 
        !            18: /* Support for multithreaded operation added by TrueCrypt Foundation */
        !            19: 
        !            20: #include "twofish.h"
        !            21: 
        !            22: #define Q_TABLES
        !            23: #define M_TABLE
        !            24: #define MK_TABLE
        !            25: #define ONE_STEP
        !            26: 
        !            27: static char *alg_name[] = { "twofish", "twofish.c", "twofish" };
        !            28: 
        !            29: static char **cipher_name()
        !            30: {
        !            31:     return alg_name;
        !            32: }
        !            33: 
        !            34: //u4byte  k_len;
        !            35: //u4byte  l_key[40];
        !            36: //u4byte  s_key[4];
        !            37: 
        !            38: /* finite field arithmetic for GF(2**8) with the modular    */
        !            39: /* polynomial x^8 + x^6 + x^5 + x^3 + 1 (0x169)             */
        !            40: 
        !            41: #define G_M 0x0169
        !            42: 
        !            43: u1byte  tab_5b[4] = { 0, G_M >> 2, G_M >> 1, (G_M >> 1) ^ (G_M >> 2) };
        !            44: u1byte  tab_ef[4] = { 0, (G_M >> 1) ^ (G_M >> 2), G_M >> 1, G_M >> 2 };
        !            45: 
        !            46: #define ffm_01(x)    (x)
        !            47: #define ffm_5b(x)   ((x) ^ ((x) >> 2) ^ tab_5b[(x) & 3])
        !            48: #define ffm_ef(x)   ((x) ^ ((x) >> 1) ^ ((x) >> 2) ^ tab_ef[(x) & 3])
        !            49: 
        !            50: u1byte ror4[16] = { 0, 8, 1, 9, 2, 10, 3, 11, 4, 12, 5, 13, 6, 14, 7, 15 };
        !            51: u1byte ashx[16] = { 0, 9, 2, 11, 4, 13, 6, 15, 8, 1, 10, 3, 12, 5, 14, 7 };
        !            52: 
        !            53: u1byte qt0[2][16] = 
        !            54: {   { 8, 1, 7, 13, 6, 15, 3, 2, 0, 11, 5, 9, 14, 12, 10, 4 },
        !            55:     { 2, 8, 11, 13, 15, 7, 6, 14, 3, 1, 9, 4, 0, 10, 12, 5 }
        !            56: };
        !            57: 
        !            58: u1byte qt1[2][16] =
        !            59: {   { 14, 12, 11, 8, 1, 2, 3, 5, 15, 4, 10, 6, 7, 0, 9, 13 }, 
        !            60:     { 1, 14, 2, 11, 4, 12, 3, 7, 6, 13, 10, 5, 15, 9, 0, 8 }
        !            61: };
        !            62: 
        !            63: u1byte qt2[2][16] = 
        !            64: {   { 11, 10, 5, 14, 6, 13, 9, 0, 12, 8, 15, 3, 2, 4, 7, 1 },
        !            65:     { 4, 12, 7, 5, 1, 6, 9, 10, 0, 14, 13, 8, 2, 11, 3, 15 }
        !            66: };
        !            67: 
        !            68: u1byte qt3[2][16] = 
        !            69: {   { 13, 7, 15, 4, 1, 2, 6, 14, 9, 11, 3, 0, 8, 5, 12, 10 },
        !            70:     { 11, 9, 5, 1, 12, 3, 13, 14, 6, 4, 7, 15, 2, 0, 8, 10 }
        !            71: };
        !            72:  
        !            73: static u1byte qp(const u4byte n, const u1byte x)
        !            74: {   u1byte  a0, a1, a2, a3, a4, b0, b1, b2, b3, b4;
        !            75: 
        !            76:     a0 = x >> 4; b0 = x & 15;
        !            77:     a1 = a0 ^ b0; b1 = ror4[b0] ^ ashx[a0];
        !            78:     a2 = qt0[n][a1]; b2 = qt1[n][b1];
        !            79:     a3 = a2 ^ b2; b3 = ror4[b2] ^ ashx[a2];
        !            80:     a4 = qt2[n][a3]; b4 = qt3[n][b3];
        !            81:     return (b4 << 4) | a4;
        !            82: };
        !            83: 
        !            84: #ifdef  Q_TABLES
        !            85: 
        !            86: u4byte  qt_gen = 0;
        !            87: u1byte  q_tab[2][256];
        !            88: 
        !            89: #define q(n,x)  q_tab[n][x]
        !            90: 
        !            91: static void gen_qtab(void)
        !            92: {   u4byte  i;
        !            93: 
        !            94:     for(i = 0; i < 256; ++i)
        !            95:     {       
        !            96:         q(0,i) = qp(0, (u1byte)i);
        !            97:         q(1,i) = qp(1, (u1byte)i);
        !            98:     }
        !            99: };
        !           100: 
        !           101: #else
        !           102: 
        !           103: #define q(n,x)  qp(n, x)
        !           104: 
        !           105: #endif
        !           106: 
        !           107: #ifdef  M_TABLE
        !           108: 
        !           109: u4byte  mt_gen = 0;
        !           110: u4byte  m_tab[4][256];
        !           111: 
        !           112: static void gen_mtab(void)
        !           113: {   u4byte  i, f01, f5b, fef;
        !           114:     
        !           115:     for(i = 0; i < 256; ++i)
        !           116:     {
        !           117:         f01 = q(1,i); f5b = ffm_5b(f01); fef = ffm_ef(f01);
        !           118:         m_tab[0][i] = f01 + (f5b << 8) + (fef << 16) + (fef << 24);
        !           119:         m_tab[2][i] = f5b + (fef << 8) + (f01 << 16) + (fef << 24);
        !           120: 
        !           121:         f01 = q(0,i); f5b = ffm_5b(f01); fef = ffm_ef(f01);
        !           122:         m_tab[1][i] = fef + (fef << 8) + (f5b << 16) + (f01 << 24);
        !           123:         m_tab[3][i] = f5b + (f01 << 8) + (fef << 16) + (f5b << 24);
        !           124:     }
        !           125: };
        !           126: 
        !           127: #define mds(n,x)    m_tab[n][x]
        !           128: 
        !           129: #else
        !           130: 
        !           131: #define fm_00   ffm_01
        !           132: #define fm_10   ffm_5b
        !           133: #define fm_20   ffm_ef
        !           134: #define fm_30   ffm_ef
        !           135: #define q_0(x)  q(1,x)
        !           136: 
        !           137: #define fm_01   ffm_ef
        !           138: #define fm_11   ffm_ef
        !           139: #define fm_21   ffm_5b
        !           140: #define fm_31   ffm_01
        !           141: #define q_1(x)  q(0,x)
        !           142: 
        !           143: #define fm_02   ffm_5b
        !           144: #define fm_12   ffm_ef
        !           145: #define fm_22   ffm_01
        !           146: #define fm_32   ffm_ef
        !           147: #define q_2(x)  q(1,x)
        !           148: 
        !           149: #define fm_03   ffm_5b
        !           150: #define fm_13   ffm_01
        !           151: #define fm_23   ffm_ef
        !           152: #define fm_33   ffm_5b
        !           153: #define q_3(x)  q(0,x)
        !           154: 
        !           155: #define f_0(n,x)    ((u4byte)fm_0##n(x))
        !           156: #define f_1(n,x)    ((u4byte)fm_1##n(x) << 8)
        !           157: #define f_2(n,x)    ((u4byte)fm_2##n(x) << 16)
        !           158: #define f_3(n,x)    ((u4byte)fm_3##n(x) << 24)
        !           159: 
        !           160: #define mds(n,x)    f_0(n,q_##n(x)) ^ f_1(n,q_##n(x)) ^ f_2(n,q_##n(x)) ^ f_3(n,q_##n(x))
        !           161: 
        !           162: #endif
        !           163: 
        !           164: static u4byte h_fun(TwofishInstance *instance, const u4byte x, const u4byte key[])
        !           165: {   u4byte  b0, b1, b2, b3;
        !           166: 
        !           167: #ifndef M_TABLE
        !           168:     u4byte  m5b_b0, m5b_b1, m5b_b2, m5b_b3;
        !           169:     u4byte  mef_b0, mef_b1, mef_b2, mef_b3;
        !           170: #endif
        !           171: 
        !           172:     b0 = extract_byte(x, 0); b1 = extract_byte(x, 1); b2 = extract_byte(x, 2); b3 = extract_byte(x, 3);
        !           173: 
        !           174:     switch(instance->k_len)
        !           175:     {
        !           176:     case 4: b0 = q(1, b0) ^ extract_byte(key[3],0);
        !           177:             b1 = q(0, b1) ^ extract_byte(key[3],1);
        !           178:             b2 = q(0, b2) ^ extract_byte(key[3],2);
        !           179:             b3 = q(1, b3) ^ extract_byte(key[3],3);
        !           180:     case 3: b0 = q(1, b0) ^ extract_byte(key[2],0);
        !           181:             b1 = q(1, b1) ^ extract_byte(key[2],1);
        !           182:             b2 = q(0, b2) ^ extract_byte(key[2],2);
        !           183:             b3 = q(0, b3) ^ extract_byte(key[2],3);
        !           184:     case 2: b0 = q(0,q(0,b0) ^ extract_byte(key[1],0)) ^ extract_byte(key[0],0);
        !           185:             b1 = q(0,q(1,b1) ^ extract_byte(key[1],1)) ^ extract_byte(key[0],1);
        !           186:             b2 = q(1,q(0,b2) ^ extract_byte(key[1],2)) ^ extract_byte(key[0],2);
        !           187:             b3 = q(1,q(1,b3) ^ extract_byte(key[1],3)) ^ extract_byte(key[0],3);
        !           188:     }
        !           189: #ifdef  M_TABLE
        !           190: 
        !           191:     return  mds(0, b0) ^ mds(1, b1) ^ mds(2, b2) ^ mds(3, b3);
        !           192: 
        !           193: #else
        !           194: 
        !           195:     b0 = q(1, b0); b1 = q(0, b1); b2 = q(1, b2); b3 = q(0, b3);
        !           196:     m5b_b0 = ffm_5b(b0); m5b_b1 = ffm_5b(b1); m5b_b2 = ffm_5b(b2); m5b_b3 = ffm_5b(b3);
        !           197:     mef_b0 = ffm_ef(b0); mef_b1 = ffm_ef(b1); mef_b2 = ffm_ef(b2); mef_b3 = ffm_ef(b3);
        !           198:     b0 ^= mef_b1 ^ m5b_b2 ^ m5b_b3; b3 ^= m5b_b0 ^ mef_b1 ^ mef_b2;
        !           199:     b2 ^= mef_b0 ^ m5b_b1 ^ mef_b3; b1 ^= mef_b0 ^ mef_b2 ^ m5b_b3;
        !           200: 
        !           201:     return b0 | (b3 << 8) | (b2 << 16) | (b1 << 24);
        !           202: 
        !           203: #endif
        !           204: };
        !           205: 
        !           206: #ifdef  MK_TABLE
        !           207: 
        !           208: #ifdef  ONE_STEP
        !           209: //u4byte  mk_tab[4][256];
        !           210: #else
        !           211: u1byte  sb[4][256];
        !           212: #endif
        !           213: 
        !           214: #define q20(x)  q(0,q(0,x) ^ extract_byte(key[1],0)) ^ extract_byte(key[0],0)
        !           215: #define q21(x)  q(0,q(1,x) ^ extract_byte(key[1],1)) ^ extract_byte(key[0],1)
        !           216: #define q22(x)  q(1,q(0,x) ^ extract_byte(key[1],2)) ^ extract_byte(key[0],2)
        !           217: #define q23(x)  q(1,q(1,x) ^ extract_byte(key[1],3)) ^ extract_byte(key[0],3)
        !           218: 
        !           219: #define q30(x)  q(0,q(0,q(1, x) ^ extract_byte(key[2],0)) ^ extract_byte(key[1],0)) ^ extract_byte(key[0],0)
        !           220: #define q31(x)  q(0,q(1,q(1, x) ^ extract_byte(key[2],1)) ^ extract_byte(key[1],1)) ^ extract_byte(key[0],1)
        !           221: #define q32(x)  q(1,q(0,q(0, x) ^ extract_byte(key[2],2)) ^ extract_byte(key[1],2)) ^ extract_byte(key[0],2)
        !           222: #define q33(x)  q(1,q(1,q(0, x) ^ extract_byte(key[2],3)) ^ extract_byte(key[1],3)) ^ extract_byte(key[0],3)
        !           223: 
        !           224: #define q40(x)  q(0,q(0,q(1, q(1, x) ^ extract_byte(key[3],0)) ^ extract_byte(key[2],0)) ^ extract_byte(key[1],0)) ^ extract_byte(key[0],0)
        !           225: #define q41(x)  q(0,q(1,q(1, q(0, x) ^ extract_byte(key[3],1)) ^ extract_byte(key[2],1)) ^ extract_byte(key[1],1)) ^ extract_byte(key[0],1)
        !           226: #define q42(x)  q(1,q(0,q(0, q(0, x) ^ extract_byte(key[3],2)) ^ extract_byte(key[2],2)) ^ extract_byte(key[1],2)) ^ extract_byte(key[0],2)
        !           227: #define q43(x)  q(1,q(1,q(0, q(1, x) ^ extract_byte(key[3],3)) ^ extract_byte(key[2],3)) ^ extract_byte(key[1],3)) ^ extract_byte(key[0],3)
        !           228: 
        !           229: static gen_mk_tab(TwofishInstance *instance, u4byte key[])
        !           230: {   u4byte  i;
        !           231:     u1byte  by;
        !           232: 
        !           233:        u4byte *l_key = instance->l_key;
        !           234:        u4byte *s_key = instance->s_key;
        !           235:        u4byte *mk_tab = instance->mk_tab;
        !           236: 
        !           237:     switch(instance->k_len)
        !           238:     {
        !           239:     case 2: for(i = 0; i < 256; ++i)
        !           240:             {
        !           241:                 by = (u1byte)i;
        !           242: #ifdef ONE_STEP
        !           243:                 mk_tab[0 + 4*i] = mds(0, q20(by)); mk_tab[1 + 4*i] = mds(1, q21(by));
        !           244:                 mk_tab[2 + 4*i] = mds(2, q22(by)); mk_tab[3 + 4*i] = mds(3, q23(by));
        !           245: #else
        !           246:                 sb[0][i] = q20(by); sb[1][i] = q21(by); 
        !           247:                 sb[2][i] = q22(by); sb[3][i] = q23(by);
        !           248: #endif
        !           249:             }
        !           250:             break;
        !           251:     
        !           252:     case 3: for(i = 0; i < 256; ++i)
        !           253:             {
        !           254:                 by = (u1byte)i;
        !           255: #ifdef ONE_STEP
        !           256:                 mk_tab[0 + 4*i] = mds(0, q30(by)); mk_tab[1 + 4*i] = mds(1, q31(by));
        !           257:                 mk_tab[2 + 4*i] = mds(2, q32(by)); mk_tab[3 + 4*i] = mds(3, q33(by));
        !           258: #else
        !           259:                 sb[0][i] = q30(by); sb[1][i] = q31(by); 
        !           260:                 sb[2][i] = q32(by); sb[3][i] = q33(by);
        !           261: #endif
        !           262:             }
        !           263:             break;
        !           264:     
        !           265:     case 4: for(i = 0; i < 256; ++i)
        !           266:             {
        !           267:                 by = (u1byte)i;
        !           268: #ifdef ONE_STEP
        !           269:                 mk_tab[0 + 4*i] = mds(0, q40(by)); mk_tab[1 + 4*i] = mds(1, q41(by));
        !           270:                 mk_tab[2 + 4*i] = mds(2, q42(by)); mk_tab[3 + 4*i] = mds(3, q43(by));
        !           271: #else
        !           272:                 sb[0][i] = q40(by); sb[1][i] = q41(by); 
        !           273:                 sb[2][i] = q42(by); sb[3][i] = q43(by);
        !           274: #endif
        !           275:             }
        !           276:     }
        !           277: };
        !           278: 
        !           279: #  ifdef ONE_STEP
        !           280: #    define g0_fun(x) ( mk_tab[0 + 4*extract_byte(x,0)] ^ mk_tab[1 + 4*extract_byte(x,1)] \
        !           281:                       ^ mk_tab[2 + 4*extract_byte(x,2)] ^ mk_tab[3 + 4*extract_byte(x,3)] )
        !           282: #    define g1_fun(x) ( mk_tab[0 + 4*extract_byte(x,3)] ^ mk_tab[1 + 4*extract_byte(x,0)] \
        !           283:                       ^ mk_tab[2 + 4*extract_byte(x,1)] ^ mk_tab[3 + 4*extract_byte(x,2)] )
        !           284: 
        !           285: 
        !           286: #  else
        !           287: #    define g0_fun(x) ( mds(0, sb[0][extract_byte(x,0)]) ^ mds(1, sb[1][extract_byte(x,1)]) \
        !           288:                       ^ mds(2, sb[2][extract_byte(x,2)]) ^ mds(3, sb[3][extract_byte(x,3)]) )
        !           289: #    define g1_fun(x) ( mds(0, sb[0][extract_byte(x,3)]) ^ mds(1, sb[1][extract_byte(x,0)]) \
        !           290:                       ^ mds(2, sb[2][extract_byte(x,1)]) ^ mds(3, sb[3][extract_byte(x,2)]) )
        !           291: #  endif
        !           292: 
        !           293: #else
        !           294: 
        !           295: #define g0_fun(x)   h_fun(instance, x,s_key)
        !           296: #define g1_fun(x)   h_fun(instance, rotl(x,8),s_key)
        !           297: 
        !           298: #endif
        !           299: 
        !           300: /* The (12,8) Reed Soloman code has the generator polynomial
        !           301: 
        !           302:   g(x) = x^4 + (a + 1/a) * x^3 + a * x^2 + (a + 1/a) * x + 1
        !           303: 
        !           304: where the coefficients are in the finite field GF(2^8) with a
        !           305: modular polynomial a^8 + a^6 + a^3 + a^2 + 1. To generate the
        !           306: remainder we have to start with a 12th order polynomial with our
        !           307: eight input bytes as the coefficients of the 4th to 11th terms. 
        !           308: That is:
        !           309: 
        !           310:   m[7] * x^11 + m[6] * x^10 ... + m[0] * x^4 + 0 * x^3 +... + 0
        !           311:   
        !           312: We then multiply the generator polynomial by m[7] * x^7 and subtract
        !           313: it - xor in GF(2^8) - from the above to eliminate the x^7 term (the 
        !           314: artihmetic on the coefficients is done in GF(2^8). We then multiply 
        !           315: the generator polynomial by x^6 * coeff(x^10) and use this to remove
        !           316: the x^10 term. We carry on in this way until the x^4 term is removed
        !           317: so that we are left with:
        !           318: 
        !           319:   r[3] * x^3 + r[2] * x^2 + r[1] 8 x^1 + r[0]
        !           320: 
        !           321: which give the resulting 4 bytes of the remainder. This is equivalent 
        !           322: to the matrix multiplication in the Twofish description but much faster 
        !           323: to implement.
        !           324: 
        !           325: */
        !           326: 
        !           327: #define G_MOD   0x0000014d
        !           328: 
        !           329: static u4byte mds_rem(u4byte p0, u4byte p1)
        !           330: {   u4byte  i, t, u;
        !           331: 
        !           332:     for(i = 0; i < 8; ++i)
        !           333:     {
        !           334:         t = p1 >> 24;   // get most significant coefficient
        !           335:         
        !           336:         p1 = (p1 << 8) | (p0 >> 24); p0 <<= 8;  // shift others up
        !           337:             
        !           338:         // multiply t by a (the primitive element - i.e. left shift)
        !           339: 
        !           340:         u = (t << 1); 
        !           341:         
        !           342:         if(t & 0x80)            // subtract modular polynomial on overflow
        !           343:         
        !           344:             u ^= G_MOD; 
        !           345: 
        !           346:         p1 ^= t ^ (u << 16);    // remove t * (a * x^2 + 1)  
        !           347: 
        !           348:         u ^= (t >> 1);          // form u = a * t + t / a = t * (a + 1 / a); 
        !           349:         
        !           350:         if(t & 0x01)            // add the modular polynomial on underflow
        !           351:         
        !           352:             u ^= G_MOD >> 1;
        !           353: 
        !           354:         p1 ^= (u << 24) | (u << 8); // remove t * (a + 1/a) * (x^3 + x)
        !           355:     }
        !           356: 
        !           357:     return p1;
        !           358: };
        !           359: 
        !           360: /* initialise the key schedule from the user supplied key   */
        !           361: 
        !           362: u4byte *twofish_set_key(TwofishInstance *instance, const u4byte in_key[], const u4byte key_len)
        !           363: {   u4byte  i, a, b, me_key[4], mo_key[4];
        !           364:        u4byte *l_key, *s_key;
        !           365: 
        !           366:        instance->l_key = (u4byte *) ((__int8 *)instance + sizeof (TwofishInstance));
        !           367:        instance->s_key = (u4byte *) ((__int8 *)instance + sizeof (TwofishInstance) + TF_L_KEY_SIZE);
        !           368:        instance->mk_tab = (u4byte *) ((__int8 *)instance + sizeof (TwofishInstance) + TF_L_KEY_SIZE + TF_S_KEY_SIZE);
        !           369: 
        !           370:        l_key = instance->l_key;
        !           371:        s_key = instance->s_key;
        !           372: 
        !           373: #ifdef Q_TABLES
        !           374:     if(!qt_gen)
        !           375:     {
        !           376:         gen_qtab(); qt_gen = 1;
        !           377:     }
        !           378: #endif
        !           379: 
        !           380: #ifdef M_TABLE
        !           381:     if(!mt_gen)
        !           382:     {
        !           383:         gen_mtab(); mt_gen = 1;
        !           384:     }
        !           385: #endif
        !           386: 
        !           387:     instance->k_len = key_len / 64;   /* 2, 3 or 4 */
        !           388: 
        !           389:     for(i = 0; i < instance->k_len; ++i)
        !           390:     {
        !           391:         a = in_key[i + i];     me_key[i] = a;
        !           392:         b = in_key[i + i + 1]; mo_key[i] = b;
        !           393:         s_key[instance->k_len - i - 1] = mds_rem(a, b);
        !           394:     }
        !           395: 
        !           396:     for(i = 0; i < 40; i += 2)
        !           397:     {
        !           398:         a = 0x01010101 * i; b = a + 0x01010101;
        !           399:         a = h_fun(instance, a, me_key);
        !           400:         b = rotl(h_fun(instance, b, mo_key), 8);
        !           401:         l_key[i] = a + b;
        !           402:         l_key[i + 1] = rotl(a + 2 * b, 9);
        !           403:     }
        !           404: 
        !           405: #ifdef MK_TABLE
        !           406:     gen_mk_tab(instance, s_key);
        !           407: #endif
        !           408: 
        !           409:     return l_key;
        !           410: };
        !           411: 
        !           412: /* encrypt a block of text  */
        !           413: 
        !           414: #define f_rnd(i)                                                    \
        !           415:     t1 = g1_fun(blk[1]); t0 = g0_fun(blk[0]);                       \
        !           416:     blk[2] = rotr(blk[2] ^ (t0 + t1 + l_key[4 * (i) + 8]), 1);      \
        !           417:     blk[3] = rotl(blk[3], 1) ^ (t0 + 2 * t1 + l_key[4 * (i) + 9]);  \
        !           418:     t1 = g1_fun(blk[3]); t0 = g0_fun(blk[2]);                       \
        !           419:     blk[0] = rotr(blk[0] ^ (t0 + t1 + l_key[4 * (i) + 10]), 1);     \
        !           420:     blk[1] = rotl(blk[1], 1) ^ (t0 + 2 * t1 + l_key[4 * (i) + 11])
        !           421: 
        !           422: void twofish_encrypt(TwofishInstance *instance, const u4byte in_blk[4], u4byte out_blk[])
        !           423: {   u4byte  t0, t1, blk[4];
        !           424: 
        !           425:        u4byte *l_key = instance->l_key;
        !           426:        u4byte *s_key = instance->s_key;
        !           427:        u4byte *mk_tab = instance->mk_tab;
        !           428: 
        !           429:     blk[0] = in_blk[0] ^ l_key[0];
        !           430:     blk[1] = in_blk[1] ^ l_key[1];
        !           431:     blk[2] = in_blk[2] ^ l_key[2];
        !           432:     blk[3] = in_blk[3] ^ l_key[3];
        !           433: 
        !           434:     f_rnd(0); f_rnd(1); f_rnd(2); f_rnd(3);
        !           435:     f_rnd(4); f_rnd(5); f_rnd(6); f_rnd(7);
        !           436: 
        !           437:     out_blk[0] = blk[2] ^ l_key[4];
        !           438:     out_blk[1] = blk[3] ^ l_key[5];
        !           439:     out_blk[2] = blk[0] ^ l_key[6];
        !           440:     out_blk[3] = blk[1] ^ l_key[7]; 
        !           441: };
        !           442: 
        !           443: /* decrypt a block of text  */
        !           444: 
        !           445: #define i_rnd(i)                                                        \
        !           446:         t1 = g1_fun(blk[1]); t0 = g0_fun(blk[0]);                       \
        !           447:         blk[2] = rotl(blk[2], 1) ^ (t0 + t1 + l_key[4 * (i) + 10]);     \
        !           448:         blk[3] = rotr(blk[3] ^ (t0 + 2 * t1 + l_key[4 * (i) + 11]), 1); \
        !           449:         t1 = g1_fun(blk[3]); t0 = g0_fun(blk[2]);                       \
        !           450:         blk[0] = rotl(blk[0], 1) ^ (t0 + t1 + l_key[4 * (i) +  8]);     \
        !           451:         blk[1] = rotr(blk[1] ^ (t0 + 2 * t1 + l_key[4 * (i) +  9]), 1)
        !           452: 
        !           453: void twofish_decrypt(TwofishInstance *instance, const u4byte in_blk[4], u4byte out_blk[4])
        !           454: {   u4byte  t0, t1, blk[4];
        !           455: 
        !           456:        u4byte *l_key = instance->l_key;
        !           457:        u4byte *s_key = instance->s_key;
        !           458:        u4byte *mk_tab = instance->mk_tab;
        !           459: 
        !           460:     blk[0] = in_blk[0] ^ l_key[4];
        !           461:     blk[1] = in_blk[1] ^ l_key[5];
        !           462:     blk[2] = in_blk[2] ^ l_key[6];
        !           463:     blk[3] = in_blk[3] ^ l_key[7];
        !           464: 
        !           465:     i_rnd(7); i_rnd(6); i_rnd(5); i_rnd(4);
        !           466:     i_rnd(3); i_rnd(2); i_rnd(1); i_rnd(0);
        !           467: 
        !           468:     out_blk[0] = blk[2] ^ l_key[0];
        !           469:     out_blk[1] = blk[3] ^ l_key[1];
        !           470:     out_blk[2] = blk[0] ^ l_key[2];
        !           471:     out_blk[3] = blk[1] ^ l_key[3]; 
        !           472: };

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