c++ mcrypt error at mcrypt_generic - c++

Question

I have the following code:
[test.cpp]
#include <mcrypt.h>
#include <string>
#include <iostream>
#include <vector>
#include <stdio.h>
#include <stdlib.h>
#include <string>
using namespace std;
int main()
{
char algo[] = "rijndael-256";
char mode[] = "cbc";
char *block_buffer=(char*)"HELLO!! MY NAME IS: ";
cout<<"here"<<endl;
string s;
char key="1234-5678-9654-7512-7895-2543-12";
char iv[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};;
MCRYPT td = mcrypt_module_open(algo, NULL, mode, NULL);
if (td == MCRYPT_FAILED) { cout<<"error"<<endl;}
int keysize=32;
int r = mcrypt_generic_init(td, key, keysize, iv);
if (r<0)
{
cout<<"error2"<<endl;
mcrypt_perror(r);
return 1;
}
//while ( fread (&block_buffer, 1, 1, stdin) == 1 ) {
int j= mcrypt_generic (td, &block_buffer, sizeof(block_buffer));
if (j!=0){std::cout<<"error encrypting"<<std::endl;} // I HAVE ERROR HERE J==0
//how to print the encrypted string??
cout<<"buffer "<<block_buffer<<endl; //this is not the encriperd string. why?
mcrypt_generic_deinit(td);
mcrypt_module_close(td);
}
I am testing the code:
$: g++ test.cpp -o tst -lmcrypt
$: ./tst
WHERE SHOULT I ADD THE PKCS 7?
I have the following method:
std::string add_pkcs7_padding(std::string s, std::size_t n)
{
const std::size_t fill = n - (s.length() % n);
s.append(fill, static_cast<char>(fill));
return s;
}
std::string strip_pkcs7_padding(std::string s, std::size_t n)
{
const std::size_t pad = static_cast<unsigned char>(*s.rbegin());
return s.substr(0, s.length() - pad);
}
I din't know when should i run it and where in my code.
NEED SOME HELP. APPRECIATE A LOT!!
EDIT:
I have error at: mcrypt_generic (td, &block_buffer, sizeof(block_buffer)); The compiler prints
that the value j=0;

Answer 1

You should invoke mcrypt_generic() with a char*, not a char** as you do:
mcrypt_generic(td, block_buffer, sizeof(block_buffer));
^^^ ^^^^^^^^^^^^^^^^^^^^
ouch!
Also, the length is wrong, as sizeof(block_buffer) is just be the size of the pointer, not the string; if anything you need strlen(block_buffer).
But this is still going to be wrong in general because you need your message to be a multiple of the block size. Use the padding function:
std::string s = add_pkcs7_padding(block_buffer, mcrypt_enc_get_block_size(td));
std::vector<char> v(s.begin(), s.end()); // this will hold the encrypted data
mcrypt_generic(td, v.data(), v.size());
By the way, your plaintext should be declared like this:
const char * block_buffer = "HELLO!! MY NAME IS: ";
^^^^^ ^^^^
constness! no explicit cast!
But why so clumsy, it's better to just use a string:
std::string plaintext = "HELLO!! MY NAME IS: ";
I think you might benefit from picking up a good C++ book and familiarizing yourself with the basics of the language a bit - it's good to have a project to work on, but most of your problems aren't really related to encryption or mcrypt, but just general C++ programming.