RE: Guest Account Theory

[sm-silva]

project.pro

QT += core gui widgets
CONFIG += c++11
TARGET = CriptoMaster
TEMPLATE = app
SOURCES += main.cpp
LIBS += -lcrypto

main.cpp

#include <QApplication>
#include <QWidget>
#include <QVBoxLayout>
#include <QLineEdit>
#include <QPushButton>
#include <QTextEdit>
#include <QLabel>
#include <QTabWidget>
#include <QMessageBox>

// OpenSSL Headers
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/crypto.h>

/**
 * CRIPTOGRAFAR: Gera Salt e IV aleatórios, deriva a chave e empacota tudo em Base64.
 */
QByteArray encrypt(const QByteArray &data, const QString &password) {
    if (data.isEmpty() || password.isEmpty()) return QByteArray();

    unsigned char key[32];
    unsigned char iv[16];
    unsigned char salt[8];

    // 1. Gerar Salt e IV aleatórios (Segurança Máxima)
    RAND_bytes(salt, sizeof(salt));
    RAND_bytes(iv, sizeof(iv));

    // 2. Derivar chave de 256 bits da senha usando o Salt
    if (PKCS5_PBKDF2_HMAC(password.toUtf8().constData(), password.length(),
                          salt, sizeof(salt), 100000, EVP_sha256(), 32, key) != 1) {
        return QByteArray();
    }

    // 3. Configurar AES-256-CBC
    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    QByteArray ciphertext;
    ciphertext.resize(data.size() + EVP_MAX_BLOCK_LENGTH);

    int len = 0, ciphertextLen = 0;
    EVP_EncryptInit_ex(ctx, EVP_aes_256_cbc(), nullptr, key, iv);
    EVP_EncryptUpdate(ctx, (unsigned char*)ciphertext.data(), &len, (unsigned char*)data.data(), data.size());
    ciphertextLen = len;
    EVP_EncryptFinal_ex(ctx, (unsigned char*)ciphertext.data() + len, &len);
    ciphertextLen += len;

    EVP_CIPHER_CTX_free(ctx);
    ciphertext.resize(ciphertextLen);

    // 4. Empacotamento: SALT(8) + IV(16) + CIPHERTEXT
    QByteArray finalPackage;
    finalPackage.append((char*)salt, 8);
    finalPackage.append((char*)iv, 16);
    finalPackage.append(ciphertext);

    // Limpeza de segurança
    OPENSSL_cleanse(key, 32);
    OPENSSL_cleanse(iv, 16);

    return finalPackage.toBase64();
}

/**
 * DESCRIPTOGRAFAR: Extrai Salt e IV do pacote, deriva a chave e recupera o texto.
 */
QByteArray decrypt(const QByteArray &base64Data, const QString &password) {
    QByteArray fullData = QByteArray::fromBase64(base64Data);

    // Verificação mínima: Salt(8) + IV(16) + pelo menos 1 bloco de dados
    if (fullData.size() < 25) return QByteArray();

    unsigned char salt[8];
    unsigned char iv[16];
    unsigned char key[32];

    // 1. Extrair os componentes do pacote
    memcpy(salt, fullData.constData(), 8);
    memcpy(iv, fullData.constData() + 8, 16);
    QByteArray ciphertext = fullData.mid(24);

    // 2. Reconstruir a chave usando o Salt extraído do pacote
    if (PKCS5_PBKDF2_HMAC(password.toUtf8().constData(), password.length(),
                          salt, 8, 100000, EVP_sha256(), 32, key) != 1) {
        return QByteArray();
    }

    // 3. Configurar Descriptografia
    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    QByteArray decryptedText;
    decryptedText.resize(ciphertext.size() + EVP_MAX_BLOCK_LENGTH);

    int len = 0, decryptedLen = 0;
    EVP_DecryptInit_ex(ctx, EVP_aes_256_cbc(), nullptr, key, iv);
    EVP_DecryptUpdate(ctx, (unsigned char*)decryptedText.data(), &len, (unsigned char*)ciphertext.data(), ciphertext.size());
    decryptedLen = len;

    // Se a senha estiver errada, o Final_ex falhará devido ao padding
    int ret = EVP_DecryptFinal_ex(ctx, (unsigned char*)decryptedText.data() + len, &len);
    decryptedLen += len;

    EVP_CIPHER_CTX_free(ctx);
    OPENSSL_cleanse(key, 32);

    if (ret != 1) return QByteArray(); // Falha na segurança (senha errada)

    decryptedText.resize(decryptedLen);
    return decryptedText;
}

// --- Interface Gráfica ---
int main(int argc, char *argv[]) {
    QApplication a(argc, argv);
    QTabWidget tabs;
    tabs.setWindowTitle("CriptoMaster AES-256");
    tabs.setMinimumSize(600, 450);

    // Aba Criptografar
    QWidget *encPage = new QWidget();
    QVBoxLayout *encLayout = new QVBoxLayout(encPage);
    QTextEdit *encInput = new QTextEdit();
    QLineEdit *encPass = new QLineEdit(); encPass->setEchoMode(QLineEdit::Password);
    QTextEdit *encOutput = new QTextEdit(); encOutput->setReadOnly(true);
    QPushButton *encBtn = new QPushButton("Criptografar e Limpar Origem");

    encLayout->addWidget(new QLabel("Texto para Trancar:")); encLayout->addWidget(encInput);
    encLayout->addWidget(new QLabel("Senha:")); encLayout->addWidget(encPass);
    encLayout->addWidget(encBtn);
    encLayout->addWidget(new QLabel("Resultado Base64 (Salve isso!):")); encLayout->addWidget(encOutput);

    // Aba Descriptografar
    QWidget *decPage = new QWidget();
    QVBoxLayout *decLayout = new QVBoxLayout(decPage);
    QTextEdit *decInput = new QTextEdit();
    QLineEdit *decPass = new QLineEdit(); decPass->setEchoMode(QLineEdit::Password);
    QTextEdit *decOutput = new QTextEdit(); decOutput->setReadOnly(true);
    QPushButton *decBtn = new QPushButton("Descriptografar");

    decLayout->addWidget(new QLabel("Código Base64:")); decLayout->addWidget(decInput);
    decLayout->addWidget(new QLabel("Senha:")); decLayout->addWidget(decPass);
    decLayout->addWidget(decBtn);
    decLayout->addWidget(new QLabel("Texto Revelado:")); decLayout->addWidget(decOutput);

    // Logica dos Botões
    QObject::connect(encBtn, &QPushButton::clicked, [&]() {
        QByteArray res = encrypt(encInput->toPlainText().toUtf8(), encPass->text());
        if(!res.isEmpty()) {
            encOutput->setPlainText(res);
            // Limpa memória sensível do campo de entrada
            QString temp = encInput->toPlainText();
            OPENSSL_cleanse((void*)temp.utf16(), temp.capacity() * 2);
            encInput->clear();
        }
    });

    QObject::connect(decBtn, &QPushButton::clicked, [&]() {
        QByteArray res = decrypt(decInput->toPlainText().toUtf8(), decPass->text());
        if (res.isEmpty()) {
            QMessageBox::critical(&tabs, "Erro de Chave", "Senha incorreta ou dados corrompidos.");
            decOutput->clear();
        } else {
            decOutput->setPlainText(QString::fromUtf8(res));
            OPENSSL_cleanse((void*)res.data(), res.capacity());
        }
    });

    tabs.addTab(encPage, "Criptografar");
    tabs.addTab(decPage, "Descriptografar");
    tabs.show();
    return a.exec();
}

---

sudo apt install build-essential libssl-dev qtbase5-dev qt5-qmake
qmake project.pro
make