QT开发（六十六）——登录对话框的验证机制

一、验证码机制

为了避免被恶意程序***，程序通常要使用安全机制。验证码机制是提供产生随机验证码，由用户识别填写来判断用户有效性的安全机制。

验证码必须动态随机产生，验证码的显示必须避开使用标准组件（如标签、文本框等），同时要增加足够的障碍难度增加程序的识别难度。

基本的解决方案如下：

A、随机产生目标验证码

B、将验证码直接绘制于登录对话框

C、验证码中的字符颜色随机变化

D、在验证码区域随机绘制噪点

二、登录对话框验证码机制实现

1、随机数产生

计算机只能产生伪随机数。

QString getRandom()
{QString ret = "";for(int i=0; i<4; i++){int c = (qrand() % 2) ? 'a' : 'A';ret += static_cast<QChar>(c + qrand() % 26);}return ret;
}

2、验证码绘制

每次绘制单个验证码，使用随机颜色的画笔

for(int i = 0; i < 4; i++){painter.setPen(m_colors[i]);painter.drawText(245 + 25*i, 150, 25, 30, Qt::AlignCenter, QString(m_verification[i]));}

3、噪点绘制

在验证码绘制矩形区域内随机位置绘制噪点

for(int i=0; i<150; i++){painter.setPen(m_colors[i%4]);painter.drawPoint(245 + qrand() % 99, 150 + qrand() % 29);}

4、代码实例

LoginDialog.h文件：

#ifndef LOGINDIALOG_H
#define LOGINDIALOG_H#include <QDialog>
#include <QLineEdit>
#include <QPushButton>
#include <QLabel>
#include <QTimer>class LoginDialog: public QDialog
{Q_OBJECT
private:QLabel UserLabel;QLabel PwdLabel;QLabel Verification;QLineEdit VerificationEdit;QLineEdit UserEdit;QLineEdit PwdEdit;QPushButton B_Login;QPushButton B_Cancel;QString m_user;QString m_pwd;Qt::GlobalColor* m_colors;QString m_verification;QTimer m_timer;
private:Qt::GlobalColor* getColors();QString getVerificationCode();void paintEvent(QPaintEvent *event);void mouseDoubleClickEvent(QMouseEvent *event);private slots:void Login();void Cancel();void onTimeOut();public:LoginDialog(QWidget *parent);QString getUser();QString getPwd();~LoginDialog();
};#endif // LOGINDIALOG_H

LoginDialog.cpp文件：

#include "LoginDialog.h"
#include <QDebug>
#include <QMessageBox>
#include <QPainter>
#include <QMouseEvent>
#include <QTime>LoginDialog::LoginDialog(QWidget *parent):QDialog(parent, Qt::WindowCloseButtonHint), UserLabel(this), PwdLabel(this),Verification(this),VerificationEdit(this), UserEdit(this), PwdEdit(this), B_Login(this),B_Cancel(this)
{UserLabel.setText("User ID:");UserLabel.move(50, 50);UserLabel.resize(60, 30);UserEdit.move(110, 50);UserEdit.resize(200, 30);PwdLabel.setText("Password:");PwdLabel.move(50, 100);PwdLabel.resize(60,30);PwdEdit.move(110, 100);PwdEdit.resize(200, 30);PwdEdit.setEchoMode(QLineEdit::Password);Verification.move(50, 150);Verification.resize(110, 30);Verification.setText("Verification Code: ");VerificationEdit.move(160, 150);VerificationEdit.resize(80, 30);B_Login.setText("Login");B_Login.move(110, 200);B_Login.resize(80, 30);B_Cancel.setText("Cancel");B_Cancel.move(230, 200);B_Cancel.resize(80, 30);setWindowTitle("Login Window");setFixedSize(400, 300);//生成伪随机种子qsrand(QTime::currentTime().second() * 1000 + QTime::currentTime().msec());m_colors = getColors();m_verification = getVerificationCode();connect(&B_Login, SIGNAL(clicked()), this, SLOT(Login()));connect(&B_Cancel, SIGNAL(clicked()), this, SLOT(Cancel()));connect(&m_timer, SIGNAL(timeout()), this, SLOT(onTimeOut()));m_timer.start(500);
}void LoginDialog::onTimeOut()
{qsrand(QTime::currentTime().second() * 1000 + QTime::currentTime().msec());m_colors = getColors();update();
}QString LoginDialog::getUser()
{return m_user;
}QString LoginDialog::getPwd()
{return m_pwd;
}void LoginDialog::Login()
{qDebug() << "login";QString verif = VerificationEdit.text().replace(" ", "");if(m_verification.toLower() == verif.toLower()){m_user = UserEdit.text().trimmed();m_pwd = PwdEdit.text();if(!(m_user.isEmpty() || m_pwd.isEmpty())){done(Accepted);}else{QMessageBox mb(this);mb.setWindowTitle("Warning Message");mb.setIcon(QMessageBox ::Warning);mb.setText("User or PassWord can't empty! \nPlease check your username or password!");mb.setStandardButtons(QMessageBox::Ok);mb.exec();}}else{QMessageBox::critical(this, "Verification Code Error", "Verification Code Error!\nPlease Enter Again.", QMessageBox::Ok);VerificationEdit.selectAll();}
}void LoginDialog::Cancel()
{qDebug() << "cancel";done(Rejected);}void LoginDialog::paintEvent(QPaintEvent *event)
{QPainter painter(this);//填充验证码绘制矩形painter.fillRect(245, 150, 100, 30, Qt::white);painter.setFont(QFont("Comic Sans MS", 12));//绘制验证码for(int i = 0; i < 4; i++){painter.setPen(m_colors[i]);painter.drawText(245 + 25*i, 150, 25, 30, Qt::AlignCenter, QString(m_verification[i]));}//绘制噪点for(int i=0; i<150; i++){painter.setPen(m_colors[i%4]);painter.drawPoint(245 + qrand() % 99, 150 + qrand() % 29);}
}Qt::GlobalColor* LoginDialog::getColors()
{static Qt::GlobalColor colors[4];for(int i=0; i<4; i++){colors[i] = static_cast<Qt::GlobalColor>(2 + qrand() % 16);}return colors;
}
//获取验证码
QString LoginDialog::getVerificationCode()
{QString ret = "";for(int i = 0; i < 4; i++){int c = (qrand() % 2) ? 'a' : 'A';ret += static_cast<QChar>(c + qrand() % 26);}return ret;
}
//双击验证码绘制矩形区域，生成新的验证码
void LoginDialog::mouseDoubleClickEvent(QMouseEvent *event)
{if(QRect(245, 150, 100, 30).contains(event->pos())){m_verification = getVerificationCode();repaint();}
}LoginDialog::~LoginDialog()
{
}

Main.cpp文件：

#include "Widget.h"
#include <QApplication>
#include "LoginDialog.h"
#include <QDebug>int main(int argc, char *argv[])
{QApplication a(argc, argv);QWidget w;LoginDialog dialog(&w);dialog.show();if(dialog.exec() == QDialog::Accepted){qDebug() <<"User:" << dialog.getUser();qDebug() << "PassWord:" << dialog.getPwd();}return a.exec();
}

代码见附件