w3 sha256 stuff

vfhash.c

#include <stdio.h>
#include <stdint.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

#include <string.h>

#include <openssl/evp.h>

#define DIGEST_SIZE 32
#define BLOCK_SIZE 1024

int main(int argc, char **argv)
{
  struct stat filestat;
  int32_t blocks, lblock;
  uint64_t fsize;
  int fd;
  unsigned char ldigest[DIGEST_SIZE];
  unsigned char msg[BLOCK_SIZE + DIGEST_SIZE];
  unsigned int md_len, i, j;

  if (argc != 2) {
    fprintf(stderr, "Usage: %s <file>\n", argv[0]);
    return 1;
  }

  if (stat(argv[1], &filestat) != 0) {
    fprintf(stderr, "Failed to stat file '%s'\n", argv[1]);
    return 1;
  }
  fsize = filestat.st_size;
  blocks = fsize / BLOCK_SIZE;
  lblock = fsize - (blocks++ * BLOCK_SIZE);

  printf("File '%s' has size %d\n", argv[1], fsize);
  printf("%d blocks to hash, last block is %d bytes\n", blocks, lblock);

  fd = open(argv[1], O_RDONLY);
  if (fd == -1) {
    fprintf(stderr, "Failed to open file '%s'\n", argv[1]);
  }

  i = 0;
  for (i = 0; i < blocks; i++) {
    uint32_t offset = fsize - lblock - (i * BLOCK_SIZE);
    uint32_t bsize = i == 0 ? lblock : BLOCK_SIZE;
    printf("[%d] Digesting block %d (%d/%d)... ", i, blocks, offset, bsize);
    if (lseek(fd, offset, SEEK_SET) == -1) {
      printf("Failed to seek file\n");
      return 1;
    };
    read(fd, msg, bsize);
    if (i != 0) {
      memcpy(msg + bsize, ldigest, DIGEST_SIZE);
      bsize += DIGEST_SIZE;
    }

    EVP_Digest(msg, bsize, ldigest, &md_len, EVP_sha256(), NULL);
    for(j = 0; j < md_len; j++)
      printf("%02x", ldigest[j]);
    printf("\n");
  }

  close(fd);
  return 0;
}