C++ Hex string to byte array - c++

Question

First off, I've Googled this question over the past few days but everything I find doesn't work. I don't receive runtime errors but when I type in the same key (in the form of a hex string) that the program generates to encrypt, decryption fails (but using the generated key throughout the program works fine). I'm trying to enter a hex string (format: 00:00:00...) and turn it into a 32-byte byte array. The input comes from getpass(). I've done this before in Java and C# but I'm new to C++ and everything seems much more complicated. Any help would be greatly appreciated :) Also I'm programming this on a linux platform so I'd like to avoid Windows-only functions.
Here is an example of what I've tried:
char *pass = getpass("Key: ");
std::stringstream converter;
std::istringstream ss( pass );
std::vector<byte> bytes;
std::string word;
while( ss >> word )
{
byte temp;
converter << std::hex << word;
converter >> temp;
bytes.push_back( temp );
}
byte* keyBytes = &bytes[0];

Answer 1

If your input has format: AA:BB:CC,
you could write something like this:
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <cstdint>
struct hex_to_byte
{
static uint8_t low(const char& value)
{
if(value <= '9' && '0' <= value)
{
return static_cast<uint8_t>(value - '0');
}
else // ('A' <= value && value <= 'F')
{
return static_cast<uint8_t>(10 + (value - 'A'));
}
}
static uint8_t high(const char& value)
{
return (low(value) << 4);
}
};
template <typename InputIterator>
std::string from_hex(InputIterator first, InputIterator last)
{
std::ostringstream oss;
while(first != last)
{
char highValue = *first++;
if(highValue == ':')
continue;
char lowValue = *first++;
char ch = (hex_to_byte::high(highValue) | hex_to_byte::low(lowValue));
oss << ch;
}
return oss.str();
}
int main()
{
std::string pass = "AB:DC:EF";
std::string bin_str = from_hex(std::begin(pass), std::end(pass));
std::vector<std::uint8_t> v(std::begin(bin_str), std::end(bin_str)); // bytes: [171, 220, 239]
return 0;
}

Answer 2

How about this?
Read it as a word and operate on it after?
You can do any size checking format checking in convert().
#include <iostream>
#include <string>
#include <vector>
char convert(char c)
{
using namespace std;
// do whatever decryption stuff you want here
return c;
}
void test()
{
using namespace std;
string word;
cin >> word;
vector<char> password;
for (int i = 0; i < word.length(); i++)
{
password.push_back(convert(word[i]));
}
for (int i = 0; i < password.size(); i++)
{
cout << password[i];
}
cout << "";
}
int main()
{
using namespace std;
char wait = ' ';
test();
cin >> wait;
}
Are there specific reasons for not using cin here?