Java中如何实现加密 详解常见加密算法的实现

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;

public class AESExample {

    public static String encrypt(String data, SecretKey secretKey) throws Exception {
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
        byte[] encryptedBytes = cipher.doFinal(data.getBytes());
        return Base64.getEncoder().encodeToString(encryptedBytes);
    }

    public static String decrypt(String encryptedData, SecretKey secretKey) throws Exception {
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, secretKey);
        byte[] decryptedBytes = cipher.doFinal(Base64.getDecoder().decode(encryptedData));
        return new String(decryptedBytes);
    }

    public static void main(String[] args) throws Exception {
        // 生成密钥
        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
        keyGenerator.init(128); // 可以选择128, 192, 或 256位
        SecretKey secretKey = keyGenerator.generateKey();

        String data = "This is a secret message.";
        String encryptedData = encrypt(data, secretKey);
        String decryptedData = decrypt(encryptedData, secretKey);

        System.out.println("Original Data: " + data);
        System.out.println("Encrypted Data: " + encryptedData);
        System.out.println("Decrypted Data: " + decryptedData);

        // 从字节数组创建密钥
        byte[] keyBytes = secretKey.getEncoded();
        SecretKey restoredKey = new SecretKeySpec(keyBytes, "AES");
        String encryptedData2 = encrypt(data, restoredKey);
        System.out.println("Encrypted Data with restored key: " + encryptedData2);
    }
}

import java.security.*;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;

import javax.crypto.Cipher;

public class RSAExample {

    public static KeyPair generateKeyPair() throws Exception {
        KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
        generator.initialize(2048); // 密钥长度
        return generator.generateKeyPair();
    }

    public static String encrypt(String data, PublicKey publicKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        byte[] encryptedBytes = cipher.doFinal(data.getBytes());
        return Base64.getEncoder().encodeToString(encryptedBytes);
    }

    public static String decrypt(String encryptedData, PrivateKey privateKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        byte[] decryptedBytes = cipher.doFinal(Base64.getDecoder().decode(encryptedData));
        return new String(decryptedBytes);
    }

    public static void main(String[] args) throws Exception {
        KeyPair keyPair = generateKeyPair();
        PublicKey publicKey = keyPair.getPublic();
        PrivateKey privateKey = keyPair.getPrivate();

        String data = "This is a secret message for RSA.";
        String encryptedData = encrypt(data, publicKey);
        String decryptedData = decrypt(encryptedData, privateKey);

        System.out.println("Original Data: " + data);
        System.out.println("Encrypted Data: " + encryptedData);
        System.out.println("Decrypted Data: " + decryptedData);

        // 公钥和私钥的存储和恢复示例
        byte[] publicKeyBytes = publicKey.getEncoded();
        byte[] privateKeyBytes = privateKey.getEncoded();

        // 恢复公钥
        X509EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicKeyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        PublicKey restoredPublicKey = keyFactory.generatePublic(publicKeySpec);

        // 恢复私钥
        PKCS8EncodedKeySpec privateKeySpec = new PKCS8EncodedKeySpec(privateKeyBytes);
        PrivateKey restoredPrivateKey = keyFactory.generatePrivate(privateKeySpec);

        String encryptedData2 = encrypt(data, restoredPublicKey);
        System.out.println("Encrypted Data with restored public key: " + encryptedData2);
    }
}

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.HexFormat;

public class SHA256Example {

    public static String hash(String data) throws NoSuchAlgorithmException {
        MessageDigest digest = MessageDigest.getInstance("SHA-256");
        byte[] hashBytes = digest.digest(data.getBytes(StandardCharsets.UTF_8));
        return HexFormat.of().formatHex(hashBytes);
    }

    public static void main(String[] args) throws NoSuchAlgorithmException {
        String data = "This is a message to be hashed.";
        String hash = hash(data);
        System.out.println("Original Data: " + data);
        System.out.println("SHA-256 Hash: " + hash);
    }
}