[YU WU]

dear all,

i am using openssl 0.9.8.e in M$ and compile in MSYS. i just want to encrypt a 
string and then decrypt later. for the encryption, it is always ok. but for 
decryption, it failed randomly. the word "randomly" means that for some cases, 
the decryption is ok, but for other cases, it failed and always gave the error 
information "Error in Decrypt final". for the failure situation, there are two 
cases: one is that the decrypted string is correct compared with the source 
string; the other is that the decrypted string is wrong since the final block 
is lost.

i really feel frustrated due to the random failure and i can't find where the 
error is. below are the encryption and decryption function. any help would be 
very appreciated.

===============>encryption function

unsigned char *encode_string (char *data, unsigned char key[], unsigned char 
iv[], int *output_len)
{
  unsigned char *encrypt;
  int buff_size, input_len, final_part;
  EVP_CIPHER_CTX ctx;
#ifdef REG_DEBUG
  FILE *fp;
#endif

  input_len = strlen(data) + 1;
  buff_size = (input_len / BUFFER + 1) * BUFFER + EVP_MAX_BLOCK_LENGTH;
  /* if(input_len + IV_LEN > BUFFER)
    buff_size = input_len + IV_LEN + EVP_MAX_BLOCK_LENGTH;
  else
    buff_size = BUFFER + EVP_MAX_BLOCK_LENGTH; */
  encrypt = (unsigned char *)malloc(buff_size * sizeof(char));
  memset(encrypt, 0, buff_size);

  EVP_CIPHER_CTX_init(&ctx);
  EVP_EncryptInit(&ctx, EVP_bf_cbc(), key, iv);  
  /* EVP_CIPHER_CTX_set_padding(&ctx, 0); */

  if(!EVP_EncryptUpdate(&ctx, encrypt, output_len, data, input_len))
  {
#ifdef REG_DEBUG
    if((fp = open_file_to_do (CRYPTO_LOG, "w")))
    {
      fprintf(fp, "Error in encrypt update.");
      fclose(fp);
    }
#endif
  }
  else
  {
    if (!EVP_EncryptFinal(&ctx, encrypt + (*output_len), &final_part))
    {
#ifdef REG_DEBUG
      if((fp = open_file_to_do (CRYPTO_LOG, "w")))
      {
    fprintf(fp, "Error in encrypt final.");
    fclose(fp);
      }
#endif
    }
    else
      *output_len += final_part;
  }
  EVP_CIPHER_CTX_cleanup(&ctx);

  return encrypt;
}


===============>decryption function
`data' is from "read" function which reads from a file and `input_len' is the 
return value of "read" function

unsigned char *decode_string (char *data, int input_len, unsigned char key[], 
unsigned char iv[], int *output_len)
{
  unsigned char *decrypt;
  int buff_size, final_part;
  EVP_CIPHER_CTX ctx;
#ifdef REG_DEBUG
  FILE *fp;
#endif

  buff_size = (input_len / BUFFER + 1) * BUFFER + EVP_MAX_BLOCK_LENGTH;
  /* if(input_len + IV_LEN > BUFFER)
    buff_size = input_len + IV_LEN + EVP_MAX_BLOCK_LENGTH;
  else
    buff_size = BUFFER + EVP_MAX_BLOCK_LENGTH; */
  decrypt = (unsigned char *)malloc(buff_size * sizeof(char));
  memset(decrypt, 0, buff_size);

  EVP_CIPHER_CTX_init(&ctx);
  EVP_DecryptInit(&ctx, EVP_bf_cbc(), key, iv);  
  /* EVP_CIPHER_CTX_set_padding(&ctx, 0); */

  if(!EVP_DecryptUpdate(&ctx, decrypt, output_len, data, input_len))
  {
#ifdef REG_DEBUG
    if((fp = open_file_to_do (CRYPTO_LOG, "w")))
    {
      fprintf(fp, "Error in Decrypt update.");
      fclose(fp);
    }
#endif
  }
  else
  {
    if (!EVP_DecryptFinal(&ctx, decrypt + (*output_len), &final_part))
    {
#ifdef REG_DEBUG
      if((fp = open_file_to_do (CRYPTO_LOG, "w")))
      {
    fprintf(fp, "Error in Decrypt final.");
    fclose(fp);
      }
#endif
    }
    else
      *output_len += final_part;
  }
  EVP_CIPHER_CTX_cleanup(&ctx);

  return decrypt;
}                                         
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