evp_digest.c

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#include <openssl/evp.h>


// crash message & cleanup
void crash( EVP_MD_CTX* ctx, const char* msg)
{
  EVP_MD_CTX_free(ctx);

  fprintf(stderr, "%s\n", msg);

  exit(1);
}




int main(int argc, char *argv[])
{

  // evp structures

  EVP_MD_CTX *mdctx;                         // EVP  Message Digest context

  const EVP_MD *md;                         // Message Digest

  unsigned char md_value[EVP_MAX_MD_SIZE];  // output byte array  (hash accumulates here)

  unsigned int md_len;                  // length of digest


  // local vars

  const char* prog_name;            // this program name
  const char* digest_str;           // name of digest  "md5"  "sha1"  "sha224"
  const char* fname;                // file to hash

  FILE* inFile = NULL;              // input file


  if (argc == 3)  // parse args
      {
    prog_name  = argv[0];
    digest_str = argv[1];
    fname      = argv[2];

      }
  else   // bad args
      {
    fprintf(stderr, "no file: specified.\n usage %s  <digest>  <filename>\n", argv[0]);
    exit(2);  // return bad arguments
      }


  // try open file
  inFile = fopen(fname, "rb");

  if ( inFile == NULL )            // fail to open
    {
      fprintf(stderr, "could not open file: %s\n", fname);

      fprintf(stderr, "usage:\t %s  <digest>  <filename>\n", prog_name );

      exit(1); // fail
    }


  // get digest type
  md = EVP_get_digestbyname(digest_str);

  if (md == NULL)  // bad digest name
      {
        fprintf( stderr, "Unknown message digest %s\n", digest_str);
        exit(2);
      }


  // new digest context
    mdctx = EVP_MD_CTX_new();

    if (EVP_DigestInit_ex2(mdctx, md, NULL) == 0 )
        crash(mdctx, "Message digest initialization failed.\n");



    // read data into a buffer and update the hash
    // 1KB at a time

    unsigned char bytedata[1024];  // buffer to read into

    size_t bytes;

    // update digest context with new bytes
     while ( (bytes = fread (bytedata, 1, 1024, inFile)) != 0 )
       {

     if( EVP_DigestUpdate(mdctx, bytedata, 1024) == 0 )
       crash(mdctx, "Message digest update failed.\n");
       }

     // finalize digest
     if (EVP_DigestFinal_ex(mdctx, md_value, &md_len) == 0 )
       crash(mdctx, "Message digest finalization failed.\n");

     // final clean up
     EVP_MD_CTX_free(mdctx);  // clean up dynamic memory



     // output

     fprintf(stdout, "%s Digest is: ", digest_str);

     for ( unsigned int i = 0; i < md_len; i++)
       fprintf(stdout, "%02x", md_value[i]);  // hex digit

    fprintf(stdout,"\n");

    return 0;

}