src/third_party/openssl/openssl/engines/ccgost/gost89.c

/**********************************************************************
 *                        gost89.c                                    *
 *             Copyright (c) 2005-2006 Cryptocom LTD                  *
 *         This file is distributed under the same license as OpenSSL *
 *                                                                    *
 *          Implementation of GOST 28147-89 encryption algorithm      *
 *            No OpenSSL libraries required to compile and use        *
 *                              this code                             *
 **********************************************************************/
#include <string.h>
#include "gost89.h"
/*-
   Substitution blocks from RFC 4357

   Note: our implementation of gost 28147-89 algorithm
   uses S-box matrix rotated 90 degrees counterclockwise, relative to
   examples given in RFC.


*/

/* Substitution blocks from test examples for GOST R 34.11-94*/
gost_subst_block GostR3411_94_TestParamSet = {
    {0X1, 0XF, 0XD, 0X0, 0X5, 0X7, 0XA, 0X4, 0X9, 0X2, 0X3, 0XE, 0X6, 0XB,
     0X8, 0XC}
    ,
    {0XD, 0XB, 0X4, 0X1, 0X3, 0XF, 0X5, 0X9, 0X0, 0XA, 0XE, 0X7, 0X6, 0X8,
     0X2, 0XC}
    ,
    {0X4, 0XB, 0XA, 0X0, 0X7, 0X2, 0X1, 0XD, 0X3, 0X6, 0X8, 0X5, 0X9, 0XC,
     0XF, 0XE}
    ,
    {0X6, 0XC, 0X7, 0X1, 0X5, 0XF, 0XD, 0X8, 0X4, 0XA, 0X9, 0XE, 0X0, 0X3,
     0XB, 0X2}
    ,
    {0X7, 0XD, 0XA, 0X1, 0X0, 0X8, 0X9, 0XF, 0XE, 0X4, 0X6, 0XC, 0XB, 0X2,
     0X5, 0X3}
    ,
    {0X5, 0X8, 0X1, 0XD, 0XA, 0X3, 0X4, 0X2, 0XE, 0XF, 0XC, 0X7, 0X6, 0X0,
     0X9, 0XB}
    ,
    {0XE, 0XB, 0X4, 0XC, 0X6, 0XD, 0XF, 0XA, 0X2, 0X3, 0X8, 0X1, 0X0, 0X7,
     0X5, 0X9}
    ,
    {0X4, 0XA, 0X9, 0X2, 0XD, 0X8, 0X0, 0XE, 0X6, 0XB, 0X1, 0XC, 0X7, 0XF,
     0X5, 0X3}
};

/* Substitution blocks for hash function 1.2.643.2.9.1.6.1  */
gost_subst_block GostR3411_94_CryptoProParamSet = {
    {0x1, 0x3, 0xA, 0x9, 0x5, 0xB, 0x4, 0xF, 0x8, 0x6, 0x7, 0xE, 0xD, 0x0,
     0x2, 0xC}
    ,
    {0xD, 0xE, 0x4, 0x1, 0x7, 0x0, 0x5, 0xA, 0x3, 0xC, 0x8, 0xF, 0x6, 0x2,
     0x9, 0xB}
    ,
    {0x7, 0x6, 0x2, 0x4, 0xD, 0x9, 0xF, 0x0, 0xA, 0x1, 0x5, 0xB, 0x8, 0xE,
     0xC, 0x3}
    ,
    {0x7, 0x6, 0x4, 0xB, 0x9, 0xC, 0x2, 0xA, 0x1, 0x8, 0x0, 0xE, 0xF, 0xD,
     0x3, 0x5}
    ,
    {0x4, 0xA, 0x7, 0xC, 0x0, 0xF, 0x2, 0x8, 0xE, 0x1, 0x6, 0x5, 0xD, 0xB,
     0x9, 0x3}
    ,
    {0x7, 0xF, 0xC, 0xE, 0x9, 0x4, 0x1, 0x0, 0x3, 0xB, 0x5, 0x2, 0x6, 0xA,
     0x8, 0xD}
    ,
    {0x5, 0xF, 0x4, 0x0, 0x2, 0xD, 0xB, 0x9, 0x1, 0x7, 0x6, 0x3, 0xC, 0xE,
     0xA, 0x8}
    ,
    {0xA, 0x4, 0x5, 0x6, 0x8, 0x1, 0x3, 0x7, 0xD, 0xC, 0xE, 0x0, 0x9, 0x2,
     0xB, 0xF}
};

/* Test paramset from GOST 28147 */
gost_subst_block Gost28147_TestParamSet = {
    {0xC, 0x6, 0x5, 0x2, 0xB, 0x0, 0x9, 0xD, 0x3, 0xE, 0x7, 0xA, 0xF, 0x4,
     0x1, 0x8}
    ,
    {0x9, 0xB, 0xC, 0x0, 0x3, 0x6, 0x7, 0x5, 0x4, 0x8, 0xE, 0xF, 0x1, 0xA,
     0x2, 0xD}
    ,
    {0x8, 0xF, 0x6, 0xB, 0x1, 0x9, 0xC, 0x5, 0xD, 0x3, 0x7, 0xA, 0x0, 0xE,
     0x2, 0x4}
    ,
    {0x3, 0xE, 0x5, 0x9, 0x6, 0x8, 0x0, 0xD, 0xA, 0xB, 0x7, 0xC, 0x2, 0x1,
     0xF, 0x4}
    ,
    {0xE, 0x9, 0xB, 0x2, 0x5, 0xF, 0x7, 0x1, 0x0, 0xD, 0xC, 0x6, 0xA, 0x4,
     0x3, 0x8}
    ,
    {0xD, 0x8, 0xE, 0xC, 0x7, 0x3, 0x9, 0xA, 0x1, 0x5, 0x2, 0x4, 0x6, 0xF,
     0x0, 0xB}
    ,
    {0xC, 0x9, 0xF, 0xE, 0x8, 0x1, 0x3, 0xA, 0x2, 0x7, 0x4, 0xD, 0x6, 0x0,
     0xB, 0x5}
    ,
    {0x4, 0x2, 0xF, 0x5, 0x9, 0x1, 0x0, 0x8, 0xE, 0x3, 0xB, 0xC, 0xD, 0x7,
     0xA, 0x6}
};

/* 1.2.643.2.2.31.1 */
gost_subst_block Gost28147_CryptoProParamSetA = {
    {0xB, 0xA, 0xF, 0x5, 0x0, 0xC, 0xE, 0x8, 0x6, 0x2, 0x3, 0x9, 0x1, 0x7,
     0xD, 0x4}
    ,
    {0x1, 0xD, 0x2, 0x9, 0x7, 0xA, 0x6, 0x0, 0x8, 0xC, 0x4, 0x5, 0xF, 0x3,
     0xB, 0xE}
    ,
    {0x3, 0xA, 0xD, 0xC, 0x1, 0x2, 0x0, 0xB, 0x7, 0x5, 0x9, 0x4, 0x8, 0xF,
     0xE, 0x6}
    ,
    {0xB, 0x5, 0x1, 0x9, 0x8, 0xD, 0xF, 0x0, 0xE, 0x4, 0x2, 0x3, 0xC, 0x7,
     0xA, 0x6}
    ,
    {0xE, 0x7, 0xA, 0xC, 0xD, 0x1, 0x3, 0x9, 0x0, 0x2, 0xB, 0x4, 0xF, 0x8,
     0x5, 0x6}
    ,
    {0xE, 0x4, 0x6, 0x2, 0xB, 0x3, 0xD, 0x8, 0xC, 0xF, 0x5, 0xA, 0x0, 0x7,
     0x1, 0x9}
    ,
    {0x3, 0x7, 0xE, 0x9, 0x8, 0xA, 0xF, 0x0, 0x5, 0x2, 0x6, 0xC, 0xB, 0x4,
     0xD, 0x1}
    ,
    {0x9, 0x6, 0x3, 0x2, 0x8, 0xB, 0x1, 0x7, 0xA, 0x4, 0xE, 0xF, 0xC, 0x0,
     0xD, 0x5}
};

/* 1.2.643.2.2.31.2 */
gost_subst_block Gost28147_CryptoProParamSetB = {
    {0x0, 0x4, 0xB, 0xE, 0x8, 0x3, 0x7, 0x1, 0xA, 0x2, 0x9, 0x6, 0xF, 0xD,
     0x5, 0xC}
    ,
    {0x5, 0x2, 0xA, 0xB, 0x9, 0x1, 0xC, 0x3, 0x7, 0x4, 0xD, 0x0, 0x6, 0xF,
     0x8, 0xE}
    ,
    {0x8, 0x3, 0x2, 0x6, 0x4, 0xD, 0xE, 0xB, 0xC, 0x1, 0x7, 0xF, 0xA, 0x0,
     0x9, 0x5}
    ,
    {0x2, 0x7, 0xC, 0xF, 0x9, 0x5, 0xA, 0xB, 0x1, 0x4, 0x0, 0xD, 0x6, 0x8,
     0xE, 0x3}
    ,
    {0x7, 0x5, 0x0, 0xD, 0xB, 0x6, 0x1, 0x2, 0x3, 0xA, 0xC, 0xF, 0x4, 0xE,
     0x9, 0x8}
    ,
    {0xE, 0xC, 0x0, 0xA, 0x9, 0x2, 0xD, 0xB, 0x7, 0x5, 0x8, 0xF, 0x3, 0x6,
     0x1, 0x4}
    ,
    {0x0, 0x1, 0x2, 0xA, 0x4, 0xD, 0x5, 0xC, 0x9, 0x7, 0x3, 0xF, 0xB, 0x8,
     0x6, 0xE}
    ,
    {0x8, 0x4, 0xB, 0x1, 0x3, 0x5, 0x0, 0x9, 0x2, 0xE, 0xA, 0xC, 0xD, 0x6,
     0x7, 0xF}
};

/* 1.2.643.2.2.31.3 */
gost_subst_block Gost28147_CryptoProParamSetC = {
    {0x7, 0x4, 0x0, 0x5, 0xA, 0x2, 0xF, 0xE, 0xC, 0x6, 0x1, 0xB, 0xD, 0x9,
     0x3, 0x8}
    ,
    {0xA, 0x9, 0x6, 0x8, 0xD, 0xE, 0x2, 0x0, 0xF, 0x3, 0x5, 0xB, 0x4, 0x1,
     0xC, 0x7}
    ,
    {0xC, 0x9, 0xB, 0x1, 0x8, 0xE, 0x2, 0x4, 0x7, 0x3, 0x6, 0x5, 0xA, 0x0,
     0xF, 0xD}
    ,
    {0x8, 0xD, 0xB, 0x0, 0x4, 0x5, 0x1, 0x2, 0x9, 0x3, 0xC, 0xE, 0x6, 0xF,
     0xA, 0x7}
    ,
    {0x3, 0x6, 0x0, 0x1, 0x5, 0xD, 0xA, 0x8, 0xB, 0x2, 0x9, 0x7, 0xE, 0xF,
     0xC, 0x4}
    ,
    {0x8, 0x2, 0x5, 0x0, 0x4, 0x9, 0xF, 0xA, 0x3, 0x7, 0xC, 0xD, 0x6, 0xE,
     0x1, 0xB}
    ,
    {0x0, 0x1, 0x7, 0xD, 0xB, 0x4, 0x5, 0x2, 0x8, 0xE, 0xF, 0xC, 0x9, 0xA,
     0x6, 0x3}
    ,
    {0x1, 0xB, 0xC, 0x2, 0x9, 0xD, 0x0, 0xF, 0x4, 0x5, 0x8, 0xE, 0xA, 0x7,
     0x6, 0x3}
};

/* 1.2.643.2.2.31.4 */
gost_subst_block Gost28147_CryptoProParamSetD = {
    {0x1, 0xA, 0x6, 0x8, 0xF, 0xB, 0x0, 0x4, 0xC, 0x3, 0x5, 0x9, 0x7, 0xD,
     0x2, 0xE}
    ,
    {0x3, 0x0, 0x6, 0xF, 0x1, 0xE, 0x9, 0x2, 0xD, 0x8, 0xC, 0x4, 0xB, 0xA,
     0x5, 0x7}
    ,
    {0x8, 0x0, 0xF, 0x3, 0x2, 0x5, 0xE, 0xB, 0x1, 0xA, 0x4, 0x7, 0xC, 0x9,
     0xD, 0x6}
    ,
    {0x0, 0xC, 0x8, 0x9, 0xD, 0x2, 0xA, 0xB, 0x7, 0x3, 0x6, 0x5, 0x4, 0xE,
     0xF, 0x1}
    ,
    {0x1, 0x5, 0xE, 0xC, 0xA, 0x7, 0x0, 0xD, 0x6, 0x2, 0xB, 0x4, 0x9, 0x3,
     0xF, 0x8}
    ,
    {0x1, 0xC, 0xB, 0x0, 0xF, 0xE, 0x6, 0x5, 0xA, 0xD, 0x4, 0x8, 0x9, 0x3,
     0x7, 0x2}
    ,
    {0xB, 0x6, 0x3, 0x4, 0xC, 0xF, 0xE, 0x2, 0x7, 0xD, 0x8, 0x0, 0x5, 0xA,
     0x9, 0x1}
    ,
    {0xF, 0xC, 0x2, 0xA, 0x6, 0x4, 0x5, 0x0, 0x7, 0x9, 0xE, 0xD, 0x1, 0xB,
     0x8, 0x3}
};

const byte CryptoProKeyMeshingKey[] = {
    0x69, 0x00, 0x72, 0x22, 0x64, 0xC9, 0x04, 0x23,
    0x8D, 0x3A, 0xDB, 0x96, 0x46, 0xE9, 0x2A, 0xC4,
    0x18, 0xFE, 0xAC, 0x94, 0x00, 0xED, 0x07, 0x12,
    0xC0, 0x86, 0xDC, 0xC2, 0xEF, 0x4C, 0xA9, 0x2B
};

/* Initialization of gost_ctx subst blocks*/
static void kboxinit(gost_ctx * c, const gost_subst_block * b)
{
    int i;

    for (i = 0; i < 256; i++) {
        c->k87[i] = (b->k8[i >> 4] << 4 | b->k7[i & 15]) << 24;
        c->k65[i] = (b->k6[i >> 4] << 4 | b->k5[i & 15]) << 16;
        c->k43[i] = (b->k4[i >> 4] << 4 | b->k3[i & 15]) << 8;
        c->k21[i] = b->k2[i >> 4] << 4 | b->k1[i & 15];

    }
}

/* Part of GOST 28147 algorithm moved into separate function */
static word32 f(gost_ctx * c, word32 x)
{
    x = c->k87[x >> 24 & 255] | c->k65[x >> 16 & 255] |
        c->k43[x >> 8 & 255] | c->k21[x & 255];
    /* Rotate left 11 bits */
    return x << 11 | x >> (32 - 11);
}

/* Low-level encryption routine - encrypts one 64 bit block*/
void gostcrypt(gost_ctx * c, const byte * in, byte * out)
{
    register word32 n1, n2;     /* As named in the GOST */
    n1 = in[0] | (in[1] << 8) | (in[2] << 16) | (in[3] << 24);
    n2 = in[4] | (in[5] << 8) | (in[6] << 16) | (in[7] << 24);
    /* Instead of swapping halves, swap names each round */

    n2 ^= f(c, n1 + c->k[0]);
    n1 ^= f(c, n2 + c->k[1]);
    n2 ^= f(c, n1 + c->k[2]);
    n1 ^= f(c, n2 + c->k[3]);
    n2 ^= f(c, n1 + c->k[4]);
    n1 ^= f(c, n2 + c->k[5]);
    n2 ^= f(c, n1 + c->k[6]);
    n1 ^= f(c, n2 + c->k[7]);

    n2 ^= f(c, n1 + c->k[0]);
    n1 ^= f(c, n2 + c->k[1]);
    n2 ^= f(c, n1 + c->k[2]);
    n1 ^= f(c, n2 + c->k[3]);
    n2 ^= f(c, n1 + c->k[4]);
    n1 ^= f(c, n2 + c->k[5]);
    n2 ^= f(c, n1 + c->k[6]);
    n1 ^= f(c, n2 + c->k[7]);

    n2 ^= f(c, n1 + c->k[0]);
    n1 ^= f(c, n2 + c->k[1]);
    n2 ^= f(c, n1 + c->k[2]);
    n1 ^= f(c, n2 + c->k[3]);
    n2 ^= f(c, n1 + c->k[4]);
    n1 ^= f(c, n2 + c->k[5]);
    n2 ^= f(c, n1 + c->k[6]);
    n1 ^= f(c, n2 + c->k[7]);

    n2 ^= f(c, n1 + c->k[7]);
    n1 ^= f(c, n2 + c->k[6]);
    n2 ^= f(c, n1 + c->k[5]);
    n1 ^= f(c, n2 + c->k[4]);
    n2 ^= f(c, n1 + c->k[3]);
    n1 ^= f(c, n2 + c->k[2]);
    n2 ^= f(c, n1 + c->k[1]);
    n1 ^= f(c, n2 + c->k[0]);

    out[0] = (byte) (n2 & 0xff);
    out[1] = (byte) ((n2 >> 8) & 0xff);
    out[2] = (byte) ((n2 >> 16) & 0xff);
    out[3] = (byte) (n2 >> 24);
    out[4] = (byte) (n1 & 0xff);
    out[5] = (byte) ((n1 >> 8) & 0xff);
    out[6] = (byte) ((n1 >> 16) & 0xff);
    out[7] = (byte) (n1 >> 24);
}

/* Low-level decryption routine. Decrypts one 64-bit block */
void gostdecrypt(gost_ctx * c, const byte * in, byte * out)
{
    register word32 n1, n2;     /* As named in the GOST */
    n1 = in[0] | (in[1] << 8) | (in[2] << 16) | (in[3] << 24);
    n2 = in[4] | (in[5] << 8) | (in[6] << 16) | (in[7] << 24);

    n2 ^= f(c, n1 + c->k[0]);
    n1 ^= f(c, n2 + c->k[1]);
    n2 ^= f(c, n1 + c->k[2]);
    n1 ^= f(c, n2 + c->k[3]);
    n2 ^= f(c, n1 + c->k[4]);
    n1 ^= f(c, n2 + c->k[5]);
    n2 ^= f(c, n1 + c->k[6]);
    n1 ^= f(c, n2 + c->k[7]);

    n2 ^= f(c, n1 + c->k[7]);
    n1 ^= f(c, n2 + c->k[6]);
    n2 ^= f(c, n1 + c->k[5]);
    n1 ^= f(c, n2 + c->k[4]);
    n2 ^= f(c, n1 + c->k[3]);
    n1 ^= f(c, n2 + c->k[2]);
    n2 ^= f(c, n1 + c->k[1]);
    n1 ^= f(c, n2 + c->k[0]);

    n2 ^= f(c, n1 + c->k[7]);
    n1 ^= f(c, n2 + c->k[6]);
    n2 ^= f(c, n1 + c->k[5]);
    n1 ^= f(c, n2 + c->k[4]);
    n2 ^= f(c, n1 + c->k[3]);
    n1 ^= f(c, n2 + c->k[2]);
    n2 ^= f(c, n1 + c->k[1]);
    n1 ^= f(c, n2 + c->k[0]);

    n2 ^= f(c, n1 + c->k[7]);
    n1 ^= f(c, n2 + c->k[6]);
    n2 ^= f(c, n1 + c->k[5]);
    n1 ^= f(c, n2 + c->k[4]);
    n2 ^= f(c, n1 + c->k[3]);
    n1 ^= f(c, n2 + c->k[2]);
    n2 ^= f(c, n1 + c->k[1]);
    n1 ^= f(c, n2 + c->k[0]);

    out[0] = (byte) (n2 & 0xff);
    out[1] = (byte) ((n2 >> 8) & 0xff);
    out[2] = (byte) ((n2 >> 16) & 0xff);
    out[3] = (byte) (n2 >> 24);
    out[4] = (byte) (n1 & 0xff);
    out[5] = (byte) ((n1 >> 8) & 0xff);
    out[6] = (byte) ((n1 >> 16) & 0xff);
    out[7] = (byte) (n1 >> 24);
}

/* Encrypts several blocks in ECB mode */
void gost_enc(gost_ctx * c, const byte * clear, byte * cipher, int blocks)
{
    int i;
    for (i = 0; i < blocks; i++) {
        gostcrypt(c, clear, cipher);
        clear += 8;
        cipher += 8;
    }
}

/* Decrypts several blocks in ECB mode */
void gost_dec(gost_ctx * c, const byte * cipher, byte * clear, int blocks)
{
    int i;
    for (i = 0; i < blocks; i++) {
        gostdecrypt(c, cipher, clear);
        clear += 8;
        cipher += 8;
    }
}

/* Encrypts several full blocks in CFB mode using 8byte IV */
void gost_enc_cfb(gost_ctx * ctx, const byte * iv, const byte * clear,
                  byte * cipher, int blocks)
{
    byte cur_iv[8];
    byte gamma[8];
    int i, j;
    const byte *in;
    byte *out;
    memcpy(cur_iv, iv, 8);
    for (i = 0, in = clear, out = cipher; i < blocks; i++, in += 8, out += 8) {
        gostcrypt(ctx, cur_iv, gamma);
        for (j = 0; j < 8; j++) {
            cur_iv[j] = out[j] = in[j] ^ gamma[j];
        }
    }
}

/* Decrypts several full blocks in CFB mode using 8byte IV */
void gost_dec_cfb(gost_ctx * ctx, const byte * iv, const byte * cipher,
                  byte * clear, int blocks)
{
    byte cur_iv[8];
    byte gamma[8];
    int i, j;
    const byte *in;
    byte *out;
    memcpy(cur_iv, iv, 8);
    for (i = 0, in = cipher, out = clear; i < blocks; i++, in += 8, out += 8) {
        gostcrypt(ctx, cur_iv, gamma);
        for (j = 0; j < 8; j++) {
            out[j] = (cur_iv[j] = in[j]) ^ gamma[j];
        }
    }
}

/* Encrypts one block using specified key */
void gost_enc_with_key(gost_ctx * c, byte * key, byte * inblock,
                       byte * outblock)
{
    gost_key(c, key);
    gostcrypt(c, inblock, outblock);
}

/* Set 256 bit  key into context */
void gost_key(gost_ctx * c, const byte * k)
{
    int i, j;
    for (i = 0, j = 0; i < 8; i++, j += 4) {
        c->k[i] =
            k[j] | (k[j + 1] << 8) | (k[j + 2] << 16) | (k[j + 3] << 24);
    }
}

/* Retrieve 256-bit key from context */
void gost_get_key(gost_ctx * c, byte * k)
{
    int i, j;
    for (i = 0, j = 0; i < 8; i++, j += 4) {
        k[j] = (byte) (c->k[i] & 0xFF);
        k[j + 1] = (byte) ((c->k[i] >> 8) & 0xFF);
        k[j + 2] = (byte) ((c->k[i] >> 16) & 0xFF);
        k[j + 3] = (byte) ((c->k[i] >> 24) & 0xFF);
    }
}

/* Initalize context. Provides default value for subst_block */
void gost_init(gost_ctx * c, const gost_subst_block * b)
{
    if (!b) {
        b = &GostR3411_94_TestParamSet;
    }
    kboxinit(c, b);
}

/* Cleans up key from context */
void gost_destroy(gost_ctx * c)
{
    int i;
    for (i = 0; i < 8; i++)
        c->k[i] = 0;
}

/*
 * Compute GOST 28147 mac block Parameters gost_ctx *c - context initalized
 * with substitution blocks and key buffer - 8-byte mac state buffer block
 * 8-byte block to process.
 */
void mac_block(gost_ctx * c, byte * buffer, const byte * block)
{
    register word32 n1, n2;     /* As named in the GOST */
    int i;
    for (i = 0; i < 8; i++) {
        buffer[i] ^= block[i];
    }
    n1 = buffer[0] | (buffer[1] << 8) | (buffer[2] << 16) | (buffer[3] << 24);
    n2 = buffer[4] | (buffer[5] << 8) | (buffer[6] << 16) | (buffer[7] << 24);
    /* Instead of swapping halves, swap names each round */

    n2 ^= f(c, n1 + c->k[0]);
    n1 ^= f(c, n2 + c->k[1]);
    n2 ^= f(c, n1 + c->k[2]);
    n1 ^= f(c, n2 + c->k[3]);
    n2 ^= f(c, n1 + c->k[4]);
    n1 ^= f(c, n2 + c->k[5]);
    n2 ^= f(c, n1 + c->k[6]);
    n1 ^= f(c, n2 + c->k[7]);

    n2 ^= f(c, n1 + c->k[0]);
    n1 ^= f(c, n2 + c->k[1]);
    n2 ^= f(c, n1 + c->k[2]);
    n1 ^= f(c, n2 + c->k[3]);
    n2 ^= f(c, n1 + c->k[4]);
    n1 ^= f(c, n2 + c->k[5]);
    n2 ^= f(c, n1 + c->k[6]);
    n1 ^= f(c, n2 + c->k[7]);

    buffer[0] = (byte) (n1 & 0xff);
    buffer[1] = (byte) ((n1 >> 8) & 0xff);
    buffer[2] = (byte) ((n1 >> 16) & 0xff);
    buffer[3] = (byte) (n1 >> 24);
    buffer[4] = (byte) (n2 & 0xff);
    buffer[5] = (byte) ((n2 >> 8) & 0xff);
    buffer[6] = (byte) ((n2 >> 16) & 0xff);
    buffer[7] = (byte) (n2 >> 24);
}

/* Get mac with specified number of bits from MAC state buffer */
void get_mac(byte * buffer, int nbits, byte * out)
{
    int nbytes = nbits >> 3;
    int rembits = nbits & 7;
    int mask = rembits ? ((1 < rembits) - 1) : 0;
    int i;
    for (i = 0; i < nbytes; i++)
        out[i] = buffer[i];
    if (rembits)
        out[i] = buffer[i] & mask;
}

/*
 * Compute mac of specified length (in bits) from data. Context should be
 * initialized with key and subst blocks
 */
int gost_mac(gost_ctx * ctx, int mac_len, const unsigned char *data,
             unsigned int data_len, unsigned char *mac)
{
    byte buffer[8] = { 0, 0, 0, 0, 0, 0, 0, 0 };
    byte buf2[8];
    unsigned int i;
    for (i = 0; i + 8 <= data_len; i += 8)
        mac_block(ctx, buffer, data + i);
    if (i < data_len) {
        memset(buf2, 0, 8);
        memcpy(buf2, data + i, data_len - i);
        mac_block(ctx, buffer, buf2);
        i += 8;
    }
    if (i == 8) {
        memset(buf2, 0, 8);
        mac_block(ctx, buffer, buf2);
    }
    get_mac(buffer, mac_len, mac);
    return 1;
}

/* Compute MAC with non-zero IV. Used in some RFC 4357 algorithms */
int gost_mac_iv(gost_ctx * ctx, int mac_len, const unsigned char *iv,
                const unsigned char *data, unsigned int data_len,
                unsigned char *mac)
{
    byte buffer[8];
    byte buf2[8];
    unsigned int i;
    memcpy(buffer, iv, 8);
    for (i = 0; i + 8 <= data_len; i += 8)
        mac_block(ctx, buffer, data + i);
    if (i < data_len) {
        memset(buf2, 0, 8);
        memcpy(buf2, data + i, data_len - i);
        mac_block(ctx, buffer, buf2);
        i += 8;
    }
    if (i == 8) {
        memset(buf2, 0, 8);
        mac_block(ctx, buffer, buf2);
    }
    get_mac(buffer, mac_len, mac);
    return 1;
}

/* Implements key meshing algorithm by modifing ctx and IV in place */
void cryptopro_key_meshing(gost_ctx * ctx, unsigned char *iv)
{
    unsigned char newkey[32], newiv[8];
    /* Set static keymeshing key */
    /* "Decrypt" key with keymeshing key */
    gost_dec(ctx, CryptoProKeyMeshingKey, newkey, 4);
    /* set new key */
    gost_key(ctx, newkey);
    /* Encrypt iv with new key */
    gostcrypt(ctx, iv, newiv);
    memcpy(iv, newiv, 8);
}