AES128 encryption libgcrypt outputs junk

Question

I am using this solved post as a reference but cannot seem to get the same result: AES128 in libgcrypt not encrypting

When I print the string to console, I get junk characters. I think it may be due to '\0' being in the string but I am not certain how to go about that.

//aes.cpp

#include "aes.h"
#include <iostream>
#include <stdio.h>

#define GCRY_CIPHER GCRY_CIPHER_AES128   // Pick the cipher here
#define GCRY_MODE GCRY_CIPHER_MODE_ECB // Pick the cipher mode here

aes::aes(std::string k)
{
    key_ = k;
    keyLength_ = gcry_cipher_get_algo_keylen(GCRY_CIPHER);

    gcry_control (GCRYCTL_DISABLE_SECMEM, 0);
    gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
    gcry_cipher_open(&handle, GCRY_CIPHER, GCRY_MODE, 0);
    gcry_cipher_setkey(handle, key_.c_str(), keyLength_);
}

void aes::encrypt(string text, std::vector<char>& ret) {
    size_t textLength = text.size() + 1;
    ret.resize(textLength);
    gcry_cipher_encrypt(handle, ret.data(), textLength, text.c_str(), textLength);
}

string aes::decrypt(std::vector<char> const& text) {
    size_t textLength = text.size() + 1;


    char * decBuffer = new char[textLength];
    gcry_cipher_decrypt(handle, decBuffer, textLength, text.data(), textLength);
    string ret (decBuffer);
    delete [] decBuffer;
    return ret;
}

//aes.h

#include <gcrypt.h>
#include <iostream>

#ifndef AES_H
#define AES_H

class aes
{
public:
    aes(std::string);
    ~aes();

    gcry_cipher_hd_t handle;
    void encrypt(std::string, std::vector<char>&);
    std::string decrypt(std::vector<char> const&); 

private:
    std::string key_;
    size_t keyLength_; 
};

#endif // AES_H

//main.cpp

#include "aes.h"
#include <iostream>

int main()
{
    std::vector<char> data;

    aes bb = aes("one test AES key");
    bb.encrypt("Some message", data);

    std::string dec = bb.decrypt(data);
    std::cout << "decrypted string " << dec << std::endl;
    return 0;
    //output gives me: decrypted string �

}

Answer 1

For AES128 in ECB mode, the size of the data to be encrypted must be a multiple of 128 bits. The plaintext and ciphertext sizes must be precisely the same.

Here's working code to give you an idea of what you need to do to make it work. But I'd strongly suggest you rethink using ECB.

#include <gcrypt.h>
#include <iostream>
#include <vector>
#include <stdio.h>

class aes
{
public:
    aes(std::string);
    ~aes() { ; }

    gcry_cipher_hd_t handle;
    void encrypt(std::string, std::vector<char>&);
    std::string decrypt(std::vector<char> const&); 

private:
    std::string key_;
    size_t keyLength_; 
};

#define GCRY_CIPHER GCRY_CIPHER_AES128
#define GCRY_MODE GCRY_CIPHER_MODE_ECB

aes::aes(std::string k)
{
    key_ = k;
    keyLength_ = gcry_cipher_get_algo_keylen(GCRY_CIPHER);

    gcry_control (GCRYCTL_DISABLE_SECMEM, 0);
    gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
    gcry_cipher_open(&handle, GCRY_CIPHER, GCRY_MODE, 0);
    gcry_cipher_setkey(handle, key_.c_str(), keyLength_);
}

void aes::encrypt(std::string text, std::vector<char>& ret)
{

    // round up to the nearest multiple of the AES block size
    while ((text.size() & 0xf) != 0xf)
        text += " ";

    size_t textLength = text.size() + 1;
    ret.resize(textLength);
    int err = gcry_cipher_encrypt(handle, ret.data(), textLength, text.c_str(), textLength);
    if (err != 0)
    {
       std::cout << "encrypt fail" <<
           gcry_strsource(err) << " " <<
           gcry_strerror(err) << std::endl;
    }
}

std::string aes::decrypt(std::vector<char> const& text) {
    size_t textLength = text.size();

    char * decBuffer = new char[textLength];

    int err=gcry_cipher_decrypt(handle, decBuffer, textLength, text.data(), textLength);
    if (err != 0)
    {
       std::cout << "decrypt fail: " <<
           gcry_strsource(err) <<  " " <<
           gcry_strerror(err) << std::endl;
     }

    std::string ret (decBuffer);
    delete [] decBuffer;
    return ret;
}

int main()
{
    std::vector<char> data;

    aes bb = aes("one test AES key");
    bb.encrypt("Some message", data);


    std::string dec = bb.decrypt(data);
    std::cout << "decrypted string " << dec << std::endl;
    return 0;
}

decrypted string Some message