OPENSSL Blowfish CBC encryption differs from PHP to C++

Question

I am trying to encrypt and decrypt a communication between a C++ library and a PHP server using OPENSSL library in both of them. I want to use the Blowfish CBC algorithm but it seems that the results are different between the C++ code and the PHP code. The C++ code is taken from here:

This is the PHP code:

<?php
function strtohex($x) 
{
    $s='';
    foreach (str_split($x) as $c) $s.=sprintf("%02X",ord($c));
    return($s);
} 


$encryptedMessage = openssl_encrypt("input", "BF-CBC", "123456", 0, "initvect");


echo $encryptedMessage;
echo "\n";
echo strtohex($encryptedMessage);

The PHP output is this:

x9jDa2WMwvQ=
78396A446132574D7776513D

This is the c++ code:

bool do_encrypt(const char *in, unsigned char *out, int *outlen, unsigned    char *key, unsigned char *iv)
{
    int buflen, tmplen;

    EVP_CIPHER_CTX ctx;
    EVP_CIPHER_CTX_init(&ctx);
    EVP_EncryptInit_ex(&ctx, EVP_bf_cbc(), nullptr, key, iv);

    if (!EVP_EncryptUpdate(&ctx, out, &buflen, (unsigned char*)in,     strlen(in)))
    {
        return false;
    }

    if (!EVP_EncryptFinal_ex(&ctx, out + buflen, &tmplen))
    {
        return false;
    }

    buflen += tmplen;
    *outlen = buflen;
    EVP_CIPHER_CTX_cleanup(&ctx);

    return true;
}

unsigned char output[2048] = { 0 };
int outLen;

auto result = do_encrypt("input", output, &outLen, (unsigned char*)"123456", (unsigned char*)"initvect");

BIGNUM *outputStr = BN_new();
BN_bin2bn(output, outLen, outputStr);

cout << base64_encode(output, outLen) << "\n";
cout << BN_bn2hex(outputStr) << "\n";

The C++ output is this:

 EfRhhWqGmSQ=
 11F461856A869924

Can someone please help me understand what I'm doing wrong? Any help will be very much appreciated.

Thanks!

Edit 1: I managed to fix the C++ code after jww's answer and it worked well. I was missing the EVP_CIPHER_CTX_set_key_length However, I couldn't make the PHP code return the same thing and eventually we decided to move to AES and it now works flawlessly. Thanks!

Answer 1

For your OpenSSL code, I believe you need to call EVP_CIPHER_CTX_set_key_length to tell the library the key is only 6 bytes.

Let me throw Crypto++ into the arena below. OpenSSL and Crypto++ will converge on the right answer once you add the missing EVP_CIPHER_CTX_set_key_length OpenSSL call. The right answer is 32CEBA7E046431EB (in hex).

I don't know what's going on with PHP:

x9jDa2WMwvQ=
78396A446132574D7776513D

Considering x is ASCII 0x78, 9 is ASCII 0x39, I'm guessing you hex encoded the Base64 string.

---

$ cat test.cxx
#include "blowfish.h"
#include "modes.h"
#include "channels.h"
#include "filters.h"
#include "base64.h"
#include "hex.h"
using namespace CryptoPP;

#include <iostream>
#include <string>
using namespace std;

int main(int argc, char* argv[])
{
  const byte key[] = "123456";   // 6
  const byte  iv[] = "initvect"; // 8
  CBC_Mode<Blowfish>::Encryption encryptor;
  encryptor.SetKeyWithIV(key, 6, iv, 8);

  string r1, r2;
  ChannelSwitch chsw;

  Base64Encoder e1(new StringSink(r1));
  HexEncoder e2(new StringSink(r2));
  chsw.AddDefaultRoute(e1);
  chsw.AddDefaultRoute(e2);

  string msg = "input";
  StringSource ss(msg, true,
    new StreamTransformationFilter(encryptor,
      new Redirector(chsw)));

  cout << r1 << endl;
  cout << r2 << endl;

  return 0;
}

The test program results in:

$ ./test.exe
Ms66fgRkMes=
32CEBA7E046431EB

---

Here's the OpenSSL portion of things. Notice EVP_EncryptInit_ex is called twice. First, EVP_EncryptInit_ex is called to set the block cipher EVP_bf_cbc. The key length is set with EVP_CIPHER_CTX_set_key_length. Then second, EVP_EncryptInit_ex is called to set the key and iv.

#include <openssl/evp.h>

#include <iostream>
#include <iomanip>
#include <stdexcept>
using namespace std;

typedef unsigned char byte;

int main()
{
  EVP_CIPHER_CTX ctx;
  EVP_CIPHER_CTX_init(&ctx);

  int rc;
  const byte key[] = "123456";   // 6
  const byte  iv[] = "initvect"; // 8

  rc = EVP_EncryptInit_ex(&ctx, EVP_bf_cbc(), NULL, 0, 0);
  if (rc != 1)
    throw runtime_error("EVP_EncryptInit_ex failed");

  rc = EVP_CIPHER_CTX_set_key_length(&ctx, 6);
  if (rc != 1)
    throw runtime_error("EVP_CIPHER_CTX_set_key_length failed");

  rc = EVP_EncryptInit_ex(&ctx, NULL, NULL, key, iv);
  if (rc != 1)
    throw runtime_error("EVP_EncryptInit_ex failed");

  const byte msg[] = "input";
  byte buf[32];
  int len1 = sizeof(buf), len2 = sizeof(buf);

  rc = EVP_EncryptUpdate(&ctx, buf, &len1, msg, 5);
  if (rc != 1)
    throw runtime_error("EVP_EncryptUpdate failed");

  rc = EVP_EncryptFinal_ex(&ctx, buf+len1, &len2);
  if (rc != 1)
    throw runtime_error("EVP_EncryptFinal_ex failed");

  for(unsigned int i=0; i<len1+len2; i++)
      cout << std::hex << setw(2) << setfill('0') << (int)buf[i];
  cout << endl;

  EVP_CIPHER_CTX_cleanup(&ctx);
  return 0;
}