import java.security.MessageDigest;

public class MD5Example {
    public static void main(String[] args) throws Exception {
        String input = "Hello, world!";
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] hash = md.digest(input.getBytes());

        StringBuilder hexString = new StringBuilder();
        for (byte b : hash) {
            hexString.append(String.format("%02x", b));
        }
        System.out.println("MD5 Hash: " + hexString.toString());
    }
}

import java.security.MessageDigest;

public class SHA256Example {
    public static void main(String[] args) throws Exception {
        String input = "Hello, world!";
        MessageDigest sha = MessageDigest.getInstance("SHA-256");
        byte[] hash = sha.digest(input.getBytes());

        StringBuilder hexString = new StringBuilder();
        for (byte b : hash) {
            hexString.append(String.format("%02x", b));
        }
        System.out.println("SHA-256 Hash: " + hexString.toString());
    }
}

import java.security.*;

public class DigitalSignatureExample {
    public static void main(String[] args) throws Exception {
        // Генерация ключей
        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
        keyGen.initialize(2048);
        KeyPair pair = keyGen.generateKeyPair();

        Signature signature = Signature.getInstance("SHA256withRSA");
        signature.initSign(pair.getPrivate());

        String data = "Important message";
        signature.update(data.getBytes());
        byte[] signedData = signature.sign();

        // Проверка подписи
        signature.initVerify(pair.getPublic());
        signature.update(data.getBytes());
        boolean isValid = signature.verify(signedData);

        System.out.println("Подпись действительна? " + isValid);
    }
}

class Alfa {
    void print(Alfa obj) {
        System.out.println("A");
    }
}

class Beta extends Alfa {
    void print(Beta obj) {
        System.out.println("B");
    }
}

public class Task210225 {
    public static void main(String[] args) {
        Alfa obj1 = new Beta();
        Alfa obj2 = new Alfa();
        obj1.print(obj2);
    }
}

import java.security.SecureRandom;
import java.util.Base64;

public class SaltExample {
    public static void main(String[] args) {
        byte[] salt = new byte[16]; // 16 байт соли
        new SecureRandom().nextBytes(salt);
        System.out.println("Сгенерированная соль: " + Base64.getEncoder().encodeToString(salt));
    }
}

import java.security.SecureRandom;
import java.util.Base64;

public class IVExample {
    public static void main(String[] args) {
        byte[] iv = new byte[16]; // IV должен быть 16 байт для AES
        new SecureRandom().nextBytes(iv);
        System.out.println("Сгенерированный IV: " + Base64.getEncoder().encodeToString(iv));
    }
}

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import java.util.Base64;

public class ECBExample {
    public static void main(String[] args) throws Exception {
        String plaintext = "AAAAAAAAAAAAAAAAAAAAAAAA"; // 24 байта - два одинаковых блока

        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
        keyGen.init(128);
        SecretKey key = keyGen.generateKey();

        Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, key);
        byte[] encrypted = cipher.doFinal(plaintext.getBytes());

        System.out.println("Зашифрованный текст (ECB): " + Base64.getEncoder().encodeToString(encrypted));
    }
}
Использовать ECB не рекомендуется!

import javax.crypto.*;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.util.Base64;

public class CBCExample {
    public static void main(String[] args) throws Exception {
        String plaintext = "Hello, Secure World!";
        byte[] key = new byte[16]; // 128-битный ключ
        byte[] iv = new byte[16];  // IV

        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
        IvParameterSpec ivSpec = new IvParameterSpec(iv);

        cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivSpec);
        byte[] encrypted = cipher.doFinal(plaintext.getBytes());

        System.out.println("Зашифрованные данные (CBC): " + Base64.getEncoder().encodeToString(encrypted));
    }
}

import javax.crypto.*;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.util.Base64;

public class AESGCMExample {
    public static void main(String[] args) throws Exception {
        String plaintext = "Hello, Secure World!";
        byte[] key = new byte[16];
        byte[] iv = new byte[12];

        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
        GCMParameterSpec gcmSpec = new GCMParameterSpec(128, iv);

        cipher.init(Cipher.ENCRYPT_MODE, keySpec, gcmSpec);
        byte[] encrypted = cipher.doFinal(plaintext.getBytes());

        System.out.println("Зашифрованные данные (GCM): " + Base64.getEncoder().encodeToString(encrypted));
    }
}
GCM – самый защищённый вариант!

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import java.util.Base64;

public class CipherExample {
    public static void main(String[] args) throws Exception {
        // Генерация ключа
        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
        keyGen.init(128); // 128-битный ключ
        SecretKey secretKey = keyGen.generateKey();

        // Создание Cipher для AES
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);

        // Шифрование данных
        String originalText = "Hello, Java Crypto!";
        byte[] encryptedBytes = cipher.doFinal(originalText.getBytes());
        System.out.println("Encrypted: " + Base64.getEncoder().encodeToString(encryptedBytes));

        // Дешифрование данных
        cipher.init(Cipher.DECRYPT_MODE, secretKey);
        byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
        System.out.println("Decrypted: " + new String(decryptedBytes));
    }
}

import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import java.util.Base64;

public class KeyGeneratorExample {
    public static void main(String[] args) throws Exception {
        // Создание KeyGenerator для AES
        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
        keyGen.init(256); // 256-битный ключ

        // Генерация ключа
        SecretKey secretKey = keyGen.generateKey();
        System.out.println("Generated Key: " + Base64.getEncoder().encodeToString(secretKey.getEncoded()));
    }
}

public class Task240225 {
    public static void main(String[] args) {
        Integer a = 1000;
        int b = 1000;
        Integer c = Integer.valueOf(1000);
        Integer d = Integer.valueOf(1000);

        System.out.println(a == b);
        System.out.println(a == c);
        System.out.println(c == d);
        System.out.println(a.equals(d));
    }
}