convert a PKCS 12 cert to PEM format

利用OpenSSL的PKCS12_parse函数进行证书格式转换的参考代码。 
目前这个函数还存在内存泄漏，这是OpenSSL 的Bug，做法上完全可以参考。

EVP_CIPHER *g_pEncAlg = NULL;
ESMTRESULT OsPEMCredConvert(FILE *fIn, char *pszP12Password, char *pszPassword, char /
*pszFilename,  BOOL fMakeCertChain)
{
  ESMTRESULT  hr = NF_S_OK;
  PKCS12     *p12 = NULL;
  EVP_PKEY   *pPkey = NULL;
  X509       *pCert = NULL;
  BIO        *pBIO = NULL;
  STACK_OF(X509) *pCaCerts=NULL;
  char        abFilename[MAXPATHLEN] = "";
  FILE       *fOut = NULL;
  int         fCerts = INFO;
  NfCtx       nfCtx;
  nfCtx.fIn  = fIn;
  nfCtx.fOut = stdout;

  CRYPTO_malloc_debug_init();
  MemCheck_start();

  do
  {
    if (fMakeCertChain && g_fOutputCaCerts)
    {
      hr = CRED_E_INCOMPATIBLE_FLAGS;
      break;
    }
    if (fMakeCertChain)
      fCerts |= CLCERTS;
    else if (g_fOutputCaCerts)
      fCerts |= CACERTS | NOKEYS;

    if ((pBIO = BIO_new(NfBIO())) == NULL)
    {
      hr = CRED_E_BIO;
      break;
    }
    BIO_ctrl(pBIO, BIO_CTRL_SET, BIO_NOCLOSE, (char *)&nfCtx);

    if ((p12 = d2i_PKCS12_bio(pBIO, &p12)) == NULL)
    {
      hr = CRED_E_P12_OPEN;
      break;
    }

    if (PKCS12_parse(p12, pszP12Password ? pszP12Password : "", &pPkey, &pCert, /
(STACK **)&pCaCerts) <= 0)  {
      hr = CRED_E_P12_PARSE;
      break;
    }


    if (pszP12Password == NULL)
    {
      if (!PKCS12_verify_mac(p12, NULL, 0))
      {
        hr = CRED_E_P12_BAD_PWD;
        break;
      }
    }
    else if (!PKCS12_verify_mac(p12, pszP12Password, -1))
    {
      hr = CRED_E_P12_BAD_PWD;
	    break;
    }

    /*  Encrypt private key with 3DES if required */
    g_pEncAlg = pszPassword != NULL ? EVP_des_ede3_cbc() : NULL;
    if (!dump_certs_keys_p12 (pBIO, p12, pszP12Password, -1, fCerts, pszPassword))
    {
      hr = CRED_E_P12_PARSE;
	break;
    }

  } while (0);

  if (fOut) fclose(fOut);
  if (pCaCerts) sk_X509_free(pCaCerts);
  if (pCert) X509_free(pCert);
  if (pPkey)EVP_PKEY_free(pPkey);
  if (p12) PKCS12_free(p12);
  if (pBIO) BIO_free(pBIO);

  ERR_free_strings();
  ERR_remove_state(0);
  EVP_cleanup();


  MemCheck_stop();
  CRYPTO_mem_leaks(stdout);

  return (hr);
}