/* dec_stub.c - CBC decoder test stub - Don Yang (uguu.org)

   01/04/05
                                                                           */
#include<assert.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#define BLOCK_COUNT  32
#define BLOCK_SIZE   (BLOCK_COUNT * 4)


#ifdef BIG_ENDIAN
static void Bswap(unsigned int *d)
{
   int i;
   for(i = 0; i < BLOCK_COUNT; i++)
   {
      *d = ((*d >> 24) & 0x000000ff)
         | ((*d >>  8) & 0x0000ff00)
         | ((*d <<  8) & 0x00ff0000)
         | ((*d << 24) & 0xff000000);
      d++;
   }
}
#endif

static void D(unsigned int *d)
{
   unsigned int i;
   for(i = 0; i < BLOCK_COUNT; i++)
      d[i] ^= ~0U;
}

static void ReadBlock(FILE *infile, /*@out@*/unsigned int *d)
{
   (void)fread(d, BLOCK_SIZE, 1, infile);
   #ifdef BIG_ENDIAN
      Bswap(d);
   #endif
}

int main(int argc, char **argv)
{
   unsigned int d[2][BLOCK_COUNT], p[BLOCK_COUNT], filesize, i, b;
   FILE *infile, *outfile;

   if( argc < 3 )
      return printf("%s <infile> <outfile>\n", *argv);
   if( (infile = fopen(*++argv, "rb")) == NULL )
      return printf("Can not open %s\n", *argv);
   if( (outfile = fopen(*++argv, "wb+")) == NULL )
      return printf("Can not create %s\n", *argv);

   /* Get file size */
   (void)fseek(infile, 0, SEEK_END);
   filesize = (unsigned int)ftell(infile);
   (void)fseek(infile, 0, SEEK_SET);
   if( filesize < BLOCK_SIZE || (filesize % BLOCK_SIZE) != 0 )
      return puts("Decrypt error");

   /* Read initialization vector */
   ReadBlock(infile, d[0]);
   D(d[b = 0]);
   memcpy(p, d[0], BLOCK_SIZE);

   /* Check file size */
   if( p[BLOCK_COUNT - 1] <= filesize - BLOCK_SIZE * 2 ||
       p[BLOCK_COUNT - 1] > filesize - BLOCK_SIZE )
      return puts("Decrypt error");
   filesize = p[BLOCK_COUNT - 1];

   /* Read padding */
   if( (filesize % BLOCK_SIZE) != 0 )
   {
      ReadBlock(infile, d[1]);
      memcpy(p, d[b = 1], BLOCK_SIZE);
      D(p);
      for(i = 0; i < BLOCK_COUNT; i++)
         p[i] ^= d[0][i];
      i = filesize % BLOCK_SIZE;
      #ifdef BIG_ENDIAN
         Bswap(p);
      #endif
      (void)fwrite((unsigned char*)p + BLOCK_SIZE - i, (size_t)i, 1, outfile);
      filesize -= i;
   }

   /* Decrypt contents */
   assert((filesize % BLOCK_SIZE) == 0);
   for(; filesize > 0; filesize -= BLOCK_SIZE)
   {
      ReadBlock(infile, d[b ^= 1]);
      memcpy(p, d[b], BLOCK_SIZE);
      D(p);
      for(i = 0; i < BLOCK_COUNT; i++)
         p[i] ^= d[b ^ 1][i];
      (void)fwrite(p, BLOCK_SIZE, 1, outfile);
   }

   (void)fclose(infile);
   (void)fclose(outfile);
   return 0;
}