/*
derived from the RSA Data Security, Inc. MD5 Message-Digest Algorithm
*/

#include <stdio.h>
#include <string.h>
#include "md5.h"


// opceniti pointer
typedef unsigned char *POINTER;

// 16 bitni word
typedef unsigned short int UINT2;

// 32 bitni word
typedef unsigned long int UINT4;

// Konstante za MD5Transform funkciju
#define S11 7
#define S12 12
#define S13 17
#define S14 22
#define S21 5
#define S22 9
#define S23 14
#define S24 20
#define S31 4
#define S32 11
#define S33 16
#define S34 23
#define S41 6
#define S42 10
#define S43 15
#define S44 21

// struktura za spremanje stanja
typedef struct {
  UINT4 state[4]; // sazetak (ABCD)
  UINT4 count[2]; // duljina poruke u bitovima, modulo 2^64
  unsigned char buffer[64]; // ulazni blok poruke (512 bita)
} MD5_CTX;

// dodatak na poruku
unsigned char PADDING[64] = {
  0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};

// pomocne funkcije
#define F(x, y, z) (((x) & (y)) | ((~x) & (z)))
#define G(x, y, z) (((x) & (z)) | ((y) & (~z)))
#define H(x, y, z) ((x) ^ (y) ^ (z))
#define I(x, y, z) ((y) ^ ((x) | (~z)))

// ROTATE_LEFT rotira x ulijevo za n bitova
#define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))

// naredba za 1. rundu
#define FF(a, b, c, d, x, s, ac) { \
 (a) += F ((b), (c), (d)) + (x) + (UINT4)(ac); \
 (a) = ROTATE_LEFT ((a), (s)); \
 (a) += (b); \
  }
// naredba za 2. rundu
#define GG(a, b, c, d, x, s, ac) { \
 (a) += G ((b), (c), (d)) + (x) + (UINT4)(ac); \
 (a) = ROTATE_LEFT ((a), (s)); \
 (a) += (b); \
  }
// naredba za 3. rundu
#define HH(a, b, c, d, x, s, ac) { \
 (a) += H ((b), (c), (d)) + (x) + (UINT4)(ac); \
 (a) = ROTATE_LEFT ((a), (s)); \
 (a) += (b); \
  }
// naredba za 3. rundu
#define II(a, b, c, d, x, s, ac) { \
 (a) += I ((b), (c), (d)) + (x) + (UINT4)(ac); \
 (a) = ROTATE_LEFT ((a), (s)); \
 (a) += (b); \
  }

// Uzima po 4 okteta sa inputa, te ih zapisuje u output po little-endian sistemu (na najnizu adresu 
// zapisuje najmanje znacajni oktet).
// Pretpostavlja da je len visekratnik broja 4
void Encode (unsigned char *output, UINT4 *input, unsigned int len)
{
  unsigned int i, j;

  for (i = 0, j = 0; j < len; i++, j += 4) {
    output[j] = (unsigned char)(input[i] & 0xff);
    output[j+1] = (unsigned char)((input[i] >> 8) & 0xff);
    output[j+2] = (unsigned char)((input[i] >> 16) & 0xff);
    output[j+3] = (unsigned char)((input[i] >> 24) & 0xff);
  }
}

// Uzima po 4 okteta sa inputa, te ih zapisuje u output po big-endian sistemu (na najnizu adresu zapisuje
// najvise znacajni oktet).
// Pretpostavlja da je len visekratnik broja 4
void Decode (UINT4 *output, unsigned char *input, unsigned int len)
{
  unsigned int i, j;
  for (i = 0, j = 0; j < len; i++, j += 4)
    output[i] = ((UINT4)input[j]) | (((UINT4)input[j+1]) << 8) |
           (((UINT4)input[j+2]) << 16) | (((UINT4)input[j+3]) << 24);
}

// Kopira podatke sa adrese input na output. len je broj podataka koje treba kopirati
void MD5_memcpy (POINTER output, POINTER input, unsigned int len)
{
  unsigned int i;
  for (i = 0; i < len; i++)
    output[i] = input[i];
}

// Pocevsi od adrese output, postavlja len okteta na vrijedost value
void MD5_memset (POINTER output, int value, unsigned int len)
{
  unsigned int i;
  for (i = 0; i < len; i++)
    ((char *)output)[i] = (char)value;
}

// Inicijalizacija
void MD5Init (MD5_CTX *context)
{
  context->count[0] = context->count[1] = 0;
  context->state[0] = 0x67452301; // A
  context->state[1] = 0xefcdab89; // B
  context->state[2] = 0x98badcfe; // C
  context->state[3] = 0x10325476; // D
}

// Osnovna transformacija. Mijenja trenutni sazetak ovisno o bloku.
void MD5Transform (UINT4 state[4], unsigned char block[64])
{
  UINT4 a = state[0], b = state[1], c = state[2], d = state[3], x[16];

  Decode (x, block, 64);

  // 1. runda
  FF (a, b, c, d, x[ 0], S11, T[ 0]); /* 1 */
  FF (d, a, b, c, x[ 1], S12, T[ 1]); /* 2 */
  FF (c, d, a, b, x[ 2], S13, T[ 2]); /* 3 */
  FF (b, c, d, a, x[ 3], S14, T[ 3]); /* 4 */
  FF (a, b, c, d, x[ 4], S11, T[ 4]); /* 5 */
  FF (d, a, b, c, x[ 5], S12, T[ 5]); /* 6 */
  FF (c, d, a, b, x[ 6], S13, T[ 6]); /* 7 */
  FF (b, c, d, a, x[ 7], S14, T[ 7]); /* 8 */
  FF (a, b, c, d, x[ 8], S11, T[ 8]); /* 9 */
  FF (d, a, b, c, x[ 9], S12, T[ 9]); /* 10 */
  FF (c, d, a, b, x[10], S13, T[10]); /* 11 */
  FF (b, c, d, a, x[11], S14, T[11]); /* 12 */
  FF (a, b, c, d, x[12], S11, T[12]); /* 13 */
  FF (d, a, b, c, x[13], S12, T[13]); /* 14 */
  FF (c, d, a, b, x[14], S13, T[14]); /* 15 */
  FF (b, c, d, a, x[15], S14, T[15]); /* 16 */

  // 2. runda
  GG (a, b, c, d, x[ 1], S21, T[16]); /* 17 */
  GG (d, a, b, c, x[ 6], S22, T[17]); /* 18 */
  GG (c, d, a, b, x[11], S23, T[18]); /* 19 */
  GG (b, c, d, a, x[ 0], S24, T[19]); /* 20 */
  GG (a, b, c, d, x[ 5], S21, T[20]); /* 21 */
  GG (d, a, b, c, x[10], S22, T[21]); /* 22 */
  GG (c, d, a, b, x[15], S23, T[22]); /* 23 */
  GG (b, c, d, a, x[ 4], S24, T[23]); /* 24 */
  GG (a, b, c, d, x[ 9], S21, T[24]); /* 25 */
  GG (d, a, b, c, x[14], S22, T[25]); /* 26 */
  GG (c, d, a, b, x[ 3], S23, T[26]); /* 27 */
  GG (b, c, d, a, x[ 8], S24, T[27]); /* 28 */
  GG (a, b, c, d, x[13], S21, T[28]); /* 29 */
  GG (d, a, b, c, x[ 2], S22, T[29]); /* 30 */
  GG (c, d, a, b, x[ 7], S23, T[30]); /* 31 */
  GG (b, c, d, a, x[12], S24, T[31]); /* 32 */

  // 3. runda
  HH (a, b, c, d, x[ 5], S31, T[32]); /* 33 */
  HH (d, a, b, c, x[ 8], S32, T[33]); /* 34 */
  HH (c, d, a, b, x[11], S33, T[34]); /* 35 */
  HH (b, c, d, a, x[14], S34, T[35]); /* 36 */
  HH (a, b, c, d, x[ 1], S31, T[36]); /* 37 */
  HH (d, a, b, c, x[ 4], S32, T[37]); /* 38 */
  HH (c, d, a, b, x[ 7], S33, T[38]); /* 39 */
  HH (b, c, d, a, x[10], S34, T[39]); /* 40 */
  HH (a, b, c, d, x[13], S31, T[40]); /* 41 */
  HH (d, a, b, c, x[ 0], S32, T[41]); /* 42 */
  HH (c, d, a, b, x[ 3], S33, T[42]); /* 43 */
  HH (b, c, d, a, x[ 6], S34, T[43]); /* 44 */
  HH (a, b, c, d, x[ 9], S31, T[44]); /* 45 */
  HH (d, a, b, c, x[12], S32, T[45]); /* 46 */
  HH (c, d, a, b, x[15], S33, T[46]); /* 47 */
  HH (b, c, d, a, x[ 2], S34, T[47]); /* 48 */

  // 4. runda
  II (a, b, c, d, x[ 0], S41, T[48]); /* 49 */
  II (d, a, b, c, x[ 7], S42, T[49]); /* 50 */
  II (c, d, a, b, x[14], S43, T[50]); /* 51 */
  II (b, c, d, a, x[ 5], S44, T[51]); /* 52 */
  II (a, b, c, d, x[12], S41, T[52]); /* 53 */
  II (d, a, b, c, x[ 3], S42, T[53]); /* 54 */
  II (c, d, a, b, x[10], S43, T[54]); /* 55 */
  II (b, c, d, a, x[ 1], S44, T[55]); /* 56 */
  II (a, b, c, d, x[ 8], S41, T[56]); /* 57 */
  II (d, a, b, c, x[15], S42, T[57]); /* 58 */
  II (c, d, a, b, x[ 6], S43, T[58]); /* 59 */
  II (b, c, d, a, x[13], S44, T[59]); /* 60 */
  II (a, b, c, d, x[ 4], S41, T[60]); /* 61 */
  II (d, a, b, c, x[11], S42, T[61]); /* 62 */
  II (c, d, a, b, x[ 2], S43, T[62]); /* 63 */
  II (b, c, d, a, x[ 9], S44, T[63]); /* 64 */

  state[0] += a;
  state[1] += b;
  state[2] += c;
  state[3] += d;

  // obrisi privremene podatke
  MD5_memset ((POINTER)x, 0, sizeof (x));
}


// Obradjuje zadanu poruku, te modificira context
void MD5Update (MD5_CTX *context, unsigned char *input, unsigned int inputLen)
{
  unsigned int i, index, partLen;

  // izracunaj broj okteta modulo 64
  index = (unsigned int)((context->count[0] >> 3) & 0x3F);

  // dodaj broj bitova bloka
  if ((context->count[0] += ((UINT4)inputLen << 3)) < ((UINT4)inputLen << 3))
    context->count[1]++;
  context->count[1] += ((UINT4)inputLen >> 29);

  partLen = 64 - index;

  // tranfsormiraj koliko god puta moze
  if (inputLen >= partLen) {
    MD5_memcpy((POINTER)&context->buffer[index], (POINTER)input, partLen);
    MD5Transform (context->state, context->buffer);

    for (i = partLen; i + 63 < inputLen; i += 64)
      MD5Transform (context->state, &input[i]);

    index = 0;
  }
  else
    i = 0;

  // spremi neobradjeni dio poruke (ostatak)
  MD5_memcpy((POINTER)&context->buffer[index], (POINTER)&input[i], inputLen-i);
}

// Finalizacija: lijepi PADDING na kraj poruke, te jos dodaje duljinu poruke
// Racuna konacni sazetak
void MD5Final (unsigned char digest[16], MD5_CTX *context)
{
  unsigned char bits[8];
  unsigned int index, padLen;

  // Sacuvaj broj bitova kao 64 bitni blok
  Encode (bits, context->count, 8);

  // nalijepi jedinicu i potrebni broj nula
  index = (unsigned int)((context->count[0] >> 3) & 0x3f);
  padLen = (index < 56) ? (56 - index) : (120 - index);
  MD5Update (context, PADDING, padLen);

  // nalijepi duljinu originalne poruke
  MD5Update (context, bits, 8);

  // spremi sazetak u varijablu digest
  Encode (digest, context->state, 16);

  // obrisi podatke
  MD5_memset ((POINTER)context, 0, sizeof (*context));
}

// Ucitava poruku iz filename_in, racuna sazetak te ga ispisuje u filename_out (string u tekstualni file)
void MD5File (char *filename_in, char *filename_out)
{
  FILE *file;
  MD5_CTX context;
  int len;
  unsigned char buffer[1024], digest[16];
  unsigned int i;

  if ((file = fopen (filename_in, "rb")) == NULL)
    printf ("Datoteka %s se ne moze otvoriti za citanje!\n", filename_in);
  else {
    // inicijaliziraj
    MD5Init (&context);
    // dok ima podataka, racunaj sazetak
    while (len = fread (buffer, 1, 1024, file))
      MD5Update (&context, buffer, len);
    // finaliziraj
    MD5Final (digest, &context);
    // zatvori ulazni file
    fclose (file);
    
    if ((file = fopen (filename_out, "w")) == NULL)
    	printf ("Datoteka %s se ne moze otvoriti za pisanje!\n", filename_out);
    {
      for (i = 0; i < 16; i++)
        fprintf (file, "%02x", digest[i]);
    }
  }
}

// glavni program
int main (int argc, char *argv[])
{
  int i;
  
  if (argc != 3)
  {
    printf("usage: ./md5.exe file_in file_out\n");
    printf("  file_in  - ulazna poruka\n");
    printf("  file_out - odrediste za sazetak poruke\n");
  }
  else
    MD5File (argv[1], argv[2]);

  return (0);
}