我们如何使用 Crypto++ 执行 AES 文件加密？

Question

I am a newbie to Crypto++. I have read the documentation on AES encryption on the Crypto++ website and I want to perform AES file encryption using it. The sample code that they have is shown below:

    #include "cryptlib.h"
#include "rijndael.h"
#include "modes.h"
#include "files.h"
#include "osrng.h"
#include "hex.h"

#include <iostream>
#include <string>

int main(int argc, char* argv[])
{
    using namespace CryptoPP;

    AutoSeededRandomPool prng;
    HexEncoder encoder(new FileSink(std::cout));

    SecByteBlock key(AES::DEFAULT_KEYLENGTH);
    SecByteBlock iv(AES::BLOCKSIZE);

    prng.GenerateBlock(key, key.size());
    prng.GenerateBlock(iv, iv.size());

    std::string plain = "CBC Mode Test";
    std::string cipher, recovered;

    std::cout << "plain text: " << plain << std::endl;

    /*********************************\
    \*********************************/

    try
    {
        CBC_Mode< AES >::Encryption e;
        e.SetKeyWithIV(key, key.size(), iv);

        StringSource s(plain, true, 
            new StreamTransformationFilter(e,
                new StringSink(cipher)
            ) // StreamTransformationFilter
        ); // StringSource
    }
    catch(const Exception& e)
    {
        std::cerr << e.what() << std::endl;
        exit(1);
    }

    /*********************************\
    \*********************************/

    std::cout << "key: ";
    encoder.Put(key, key.size());
    encoder.MessageEnd();
    std::cout << std::endl;

    std::cout << "iv: ";
    encoder.Put(iv, iv.size());
    encoder.MessageEnd();
    std::cout << std::endl;

    std::cout << "cipher text: ";
    encoder.Put((const byte*)&cipher[0], cipher.size());
    encoder.MessageEnd();
    std::cout << std::endl;
    
    /*********************************\
    \*********************************/

    try
    {
        CBC_Mode< AES >::Decryption d;
        d.SetKeyWithIV(key, key.size(), iv);

        StringSource s(cipher, true, 
            new StreamTransformationFilter(d,
                new StringSink(recovered)
            ) // StreamTransformationFilter
        ); // StringSource

        std::cout << "recovered text: " << recovered << std::endl;
    }
    catch(const Exception& e)
    {
        std::cerr << e.what() << std::endl;
        exit(1);
    }

    return 0;
}

I have read the filesink and filesource documentation too but I cant actually get how to apply that in the code given above. Any help would be appreciated. https://www.cryptopp.com/wiki/Advanced_Encryption_Standard

Answer 1

Start simple. Crypto is complex with lots of extra bits to include. For a first trial you need a key, a mode (CBC is reasonably simple) and an IV (initialisation vector). Set that up, test it and get it working. Then you can add things like key derivation and try the more complex modes such as GCM.