AES encryption C++ (can't decrypt encrypted file)

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I'm playing around with AES and write the iv and derived key to the file so that I use it later for decryption...

following function encrypts the file and saves the iv and derived key into the file, it also saves encrypted text into separate file:

void MainWindow::on_button_encrypt() try
{
    using namespace std;
    using namespace Gtk;
    using namespace CryptoPP;

    fstream file;

    file.open(m_file_name + ".aes", std::ios::out | std::ios::trunc);
    if (file.is_open())
    {
        // get the plain password:
        SecByteBlock password;
        password_dialog get_passwd(password);
        get_passwd.run();


        // generate random salt
        const int SALT_SIZE = 32;
        SecByteBlock salt(SALT_SIZE);
        AutoSeededRandomPool prng;
        prng.GenerateBlock(salt.BytePtr(), SALT_SIZE);


        // derive a key from password and salt:
        SecByteBlock key(AES::DEFAULT_KEYLENGTH);
        PKCS5_PBKDF2_HMAC<SHA512> gen;
        gen.DeriveKey(key.BytePtr(), key.size(), 1, password.BytePtr(), password.size(), salt.BytePtr(), salt.size(), 200);


        // genereate random iv:
        SecByteBlock iv(AES::BLOCKSIZE);
        OS_GenerateRandomBlock(false, iv.BytePtr(), AES::BLOCKSIZE);


        // encrypt plain text:
        AES::Encryption enc(key.BytePtr(), AES::DEFAULT_KEYLENGTH);
        CBC_Mode_ExternalCipher::Encryption mode(enc, iv);

        string cipher_text;
        StringSink* sink = new StringSink(cipher_text);
        StreamTransformationFilter encryptor(mode, sink);

        string plain_text = m_file_buffer->get_text();
        encryptor.Put(reinterpret_cast<const byte*>(plain_text.c_str()), plain_text.length() + 1);
        encryptor.MessageEnd();

        // write the result:
        file << cipher_text.c_str();
        file.close();
        file.open(m_file_name + ".key", std::ios::out | std::ios::trunc);
        file << key << '\n' << iv;
        file.close();
   }
}

The above function writes the iv and derived key to the file.

0000000002F9F140

0000000002F9F4E0

Following function is supposed to read the file and decrypt it by using the *.key file:

void MainWindow::on_button_decrypt()
{
    using namespace std;
    using namespace CryptoPP;
    Gtk::MessageDialog info("Info");

    fstream file;
    file.open("decrypted.txt", ios::out | ios::trunc);
    if (file.is_open())
    {
        // read the key:
        fstream stream;
        string input;

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


        stream.open("test.txt.key", std::ios::in);

        if (stream.is_open())
        {
            getline(stream, input);
            key.Assign(reinterpret_cast<const byte*>(input.c_str()), input.size());
            input.clear();
            getline(stream, input);
            iv.Assign(reinterpret_cast<const byte*>(input.c_str()), input.size());
        }
        else
        {
            info.set_secondary_text("can't read key file");
            info.run();
            return;
        }


        // decrypt:
        AES::Decryption dec(key, AES::DEFAULT_KEYLENGTH);
        CBC_Mode_ExternalCipher::Decryption mode(dec, iv);

        string plain_text;
        StringSink* sink = new StringSink(plain_text);
        StreamTransformationFilter decryptor(mode, sink);

        try
        {
            // get encrypted text from buffer (obtained from other function):
            string cipher_text = m_file_buffer->get_text();
            decryptor.Put(reinterpret_cast<const byte*>(cipher_text.c_str()), cipher_text.size());
            decryptor.MessageEnd();
            file << plain_text;
            file.close();
        }
        catch (CryptoPP::Exception& ex)
        {
            info.set_secondary_text(ex.what());
            info.run();
        }
    }
}

CryptoPP trows an exception while decrypting saying this:

FileTransformationFilter: ciphertext length is not multiple of a block size.

How ever it does not throw anything if decryption process is done in first function ( on_btn_encrypt() ) no file is read there, so it looks I'm having problem with reading encrypted file but have no idea how?

This is content of encrypted file: &`OôÍoYjÜMe×Q°Þ

plaintext is: some text

Do you see what am I missing here? thanks so much!

asked 38 secs ago

codekiddy

1,382

AES encryption C++ (can't decrypt encrypted file)