Java之加密算法

加密算法主要分為對稱加密、非對稱加密、Hash加密。

一、何為對稱加密？

　　對稱加密是指對稱密碼編碼技術，它的特點是文件加密和解密使用相同的密鑰加密。

對稱機密的密鑰一般小於256bit。因為就密鑰而言，如果加密的密鑰越大，則其計算的復雜度越高，所需要的時間越長，而如果使用的密鑰較小，則很容易破解，所以密鑰的大小需根據業務需求去選擇。

通常，加密的算法有：DES、3DES、Blowfish、IDEA、RC4、RC5、RC6和AES 。

代碼段引用：https://blog.csdn.net/chengbinbbs/article/details/78640589

public class DESUtil {

    private static final String KEY_ALGORITHM = "DES";
    private static final String DEFAULT_CIPHER_ALGORITHM = "DES/ECB/PKCS5Padding";//默認的加密算法

    /**
     * DES 加密操作
     *
     * @param content 待加密內容
     * @param key 加密密鑰
     * @return 返回Base64轉碼后的加密數據
     */
    public static String encrypt(String content, String key) {
        try {
            Cipher cipher = Cipher.getInstance(DEFAULT_CIPHER_ALGORITHM);// 創建密碼器

            byte[] byteContent = content.getBytes("utf-8");

            cipher.init(Cipher.ENCRYPT_MODE, getSecretKey(key));// 初始化為加密模式的密碼器

            byte[] result = cipher.doFinal(byteContent);// 加密

            return Base64.encodeBase64String(result);//通過Base64轉碼返回
        } catch (Exception ex) {
            Logger.getLogger(DESUtil.class.getName()).log(Level.SEVERE, null, ex);
        }

        return null;
    }

    /**
     * DES 解密操作
     *
     * @param content
     * @param key
     * @return
     */
    public static String decrypt(String content, String key) {

        try {
            //實例化
            Cipher cipher = Cipher.getInstance(DEFAULT_CIPHER_ALGORITHM);

            //使用密鑰初始化，設置為解密模式
            cipher.init(Cipher.DECRYPT_MODE, getSecretKey(key));

            //執行操作
            byte[] result = cipher.doFinal(Base64.decodeBase64(content));

            return new String(result, "utf-8");
        } catch (Exception ex) {
            Logger.getLogger(DESUtil.class.getName()).log(Level.SEVERE, null, ex);
        }

        return null;
    }

    /**
     * 生成加密秘鑰
     *
     * @return
     */
    private static SecretKeySpec getSecretKey(final String key) {
        //返回生成指定算法密鑰生成器的 KeyGenerator 對象
        KeyGenerator kg = null;

        try {
            kg = KeyGenerator.getInstance(KEY_ALGORITHM);

            //DES 要求密鑰長度為 56
            kg.init(56, new SecureRandom(key.getBytes()));

            //生成一個密鑰
            SecretKey secretKey = kg.generateKey();

            return new SecretKeySpec(secretKey.getEncoded(), KEY_ALGORITHM);// 轉換為DES專用密鑰
        } catch (NoSuchAlgorithmException ex) {
            Logger.getLogger(DESUtil.class.getName()).log(Level.SEVERE, null, ex);
        }

        return null;
    }

    public static void main(String[] args) {
        String content = "hello,您好";
        String key = "sde@5f98H*^hsff%dfs$r344&df8543*er";
        System.out.println("content:" + content);
        String s1 = DESUtil.encrypt(content, key);
        System.out.println("s1:" + s1);
        System.out.println("s2:"+ DESUtil.decrypt(s1, key));

    }

}

　　

二、非對稱加密

何為非對稱加密？

　　非對稱加密是指加密和解密使用兩個不同的密鑰，它包含一對密鑰--私鑰(誰拿誰負責安全)和公鑰。不管是公鑰還是私鑰都可以進行加密和解密操作，即使用公鑰加密，只能使用對應的私鑰進行解密(應用簽名)，反之，使用私鑰加密，只能使用對應的公鑰解密(應用加密)。

通常，非對稱加密的算法有：RSA、ECC（移動設備用）、Diffie-Hellman、El Gamal、DSA（數字簽名用）

代碼段引用：https://blog.csdn.net/chengbinbbs/article/details/78640589

public class RSAUtils {

    /**
     * 加密算法RSA
     */
    public static final String KEY_ALGORITHM = "RSA";

    /**
     * 簽名算法
     */
    public static final String SIGNATURE_ALGORITHM = "MD5withRSA";

    /**
     * 獲取公鑰的key
     */
    private static final String PUBLIC_KEY = "RSAPublicKey";

    /**
     * 獲取私鑰的key
     */
    private static final String PRIVATE_KEY = "RSAPrivateKey";

    /**
     * RSA最大加密明文大小
     */
    private static final int MAX_ENCRYPT_BLOCK = 117;

    /**
     * RSA最大解密密文大小
     */
    private static final int MAX_DECRYPT_BLOCK = 128;

    /**
     * <p>
     * 生成密鑰對(公鑰和私鑰)
     * </p>
     *
     * @return
     * @throws Exception
     */
    public static Map<String, Object> genKeyPair() throws Exception {
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(KEY_ALGORITHM);
        keyPairGen.initialize(1024);
        KeyPair keyPair = keyPairGen.generateKeyPair();
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
        Map<String, Object> keyMap = new HashMap<String, Object>(2);
        keyMap.put(PUBLIC_KEY, publicKey);
        keyMap.put(PRIVATE_KEY, privateKey);
        return keyMap;
    }

    /**
     * <p>
     * 用私鑰對信息生成數字簽名
     * </p>
     *
     * @param data 已加密數據
     * @param privateKey 私鑰(BASE64編碼)
     *
     * @return
     * @throws Exception
     */
    public static String sign(byte[] data, String privateKey) throws Exception {
        byte[] keyBytes = Base64Utils.decode(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        PrivateKey privateK = keyFactory.generatePrivate(pkcs8KeySpec);
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initSign(privateK);
        signature.update(data);
        return Base64Utils.encode(signature.sign());
    }

    /**
     * <p>
     * 校驗數字簽名
     * </p>
     *
     * @param data 已加密數據
     * @param publicKey 公鑰(BASE64編碼)
     * @param sign 數字簽名
     *
     * @return
     * @throws Exception
     *
     */
    public static boolean verify(byte[] data, String publicKey, String sign)
            throws Exception {
        byte[] keyBytes = Base64Utils.decode(publicKey);
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        PublicKey publicK = keyFactory.generatePublic(keySpec);
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initVerify(publicK);
        signature.update(data);
        return signature.verify(Base64Utils.decode(sign));
    }

    /**
     * <P>
     * 私鑰解密
     * </p>
     *
     * @param encryptedData 已加密數據
     * @param privateKey 私鑰(BASE64編碼)
     * @return
     * @throws Exception
     */
    public static byte[] decryptByPrivateKey(byte[] encryptedData, String privateKey)
            throws Exception {
        byte[] keyBytes = Base64Utils.decode(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key privateK = keyFactory.generatePrivate(pkcs8KeySpec);
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.DECRYPT_MODE, privateK);
        int inputLen = encryptedData.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;
        // 對數據分段解密
        while (inputLen - offSet > 0) {
            if (inputLen - offSet > MAX_DECRYPT_BLOCK) {
                cache = cipher.doFinal(encryptedData, offSet, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        return decryptedData;
    }

    /**
     * <p>
     * 公鑰解密
     * </p>
     *
     * @param encryptedData 已加密數據
     * @param publicKey 公鑰(BASE64編碼)
     * @return
     * @throws Exception
     */
    public static byte[] decryptByPublicKey(byte[] encryptedData, String publicKey)
            throws Exception {
        byte[] keyBytes = Base64Utils.decode(publicKey);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key publicK = keyFactory.generatePublic(x509KeySpec);
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.DECRYPT_MODE, publicK);
        int inputLen = encryptedData.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;
        // 對數據分段解密
        while (inputLen - offSet > 0) {
            if (inputLen - offSet > MAX_DECRYPT_BLOCK) {
                cache = cipher.doFinal(encryptedData, offSet, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        return decryptedData;
    }

    /**
     * <p>
     * 公鑰加密
     * </p>
     *
     * @param data 源數據
     * @param publicKey 公鑰(BASE64編碼)
     * @return
     * @throws Exception
     */
    public static byte[] encryptByPublicKey(byte[] data, String publicKey)
            throws Exception {
        byte[] keyBytes = Base64Utils.decode(publicKey);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key publicK = keyFactory.generatePublic(x509KeySpec);
        // 對數據加密
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.ENCRYPT_MODE, publicK);
        int inputLen = data.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;
        // 對數據分段加密
        while (inputLen - offSet > 0) {
            if (inputLen - offSet > MAX_ENCRYPT_BLOCK) {
                cache = cipher.doFinal(data, offSet, MAX_ENCRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(data, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_ENCRYPT_BLOCK;
        }
        byte[] encryptedData = out.toByteArray();
        out.close();
        return encryptedData;
    }

    /**
     * <p>
     * 私鑰加密
     * </p>
     *
     * @param data 源數據
     * @param privateKey 私鑰(BASE64編碼)
     * @return
     * @throws Exception
     */
    public static byte[] encryptByPrivateKey(byte[] data, String privateKey)
            throws Exception {
        byte[] keyBytes = Base64Utils.decode(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key privateK = keyFactory.generatePrivate(pkcs8KeySpec);
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.ENCRYPT_MODE, privateK);
        int inputLen = data.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;
        // 對數據分段加密
        while (inputLen - offSet > 0) {
            if (inputLen - offSet > MAX_ENCRYPT_BLOCK) {
                cache = cipher.doFinal(data, offSet, MAX_ENCRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(data, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_ENCRYPT_BLOCK;
        }
        byte[] encryptedData = out.toByteArray();
        out.close();
        return encryptedData;
    }

    /**
     * <p>
     * 獲取私鑰
     * </p>
     *
     * @param keyMap 密鑰對
     * @return
     * @throws Exception
     */
    public static String getPrivateKey(Map<String, Object> keyMap)
            throws Exception {
        Key key = (Key) keyMap.get(PRIVATE_KEY);
        return Base64Utils.encode(key.getEncoded());
    }

    /**
     * <p>
     * 獲取公鑰
     * </p>
     *
     * @param keyMap 密鑰對
     * @return
     * @throws Exception
     */
    public static String getPublicKey(Map<String, Object> keyMap)
            throws Exception {
        Key key = (Key) keyMap.get(PUBLIC_KEY);
        return Base64Utils.encode(key.getEncoded());
    }

}

　　

三、Hash加密算法

何為Hash算法？
　　Hash算法是一種單向的加密算法，即無法解密(依目前的計算力，還是可以使用暴力破解，MD5聽說被破解過)。

通常，Hash算法有：MD2、MD4、MD5、HAVAL、SHA

import java.security.MessageDigest;
import java.util.logging.Logger;

/**
 * MD5加密算法
 */
public class MD5 {

    public static String MD5(String key) {
        char hexDigits[] = {
                '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
        };
        try {
            byte[] btInput = key.getBytes();
            // 獲得MD5摘要算法的 MessageDigest 對象
            MessageDigest mdInst = MessageDigest.getInstance("MD5");
            // 使用指定的字節更新摘要
            mdInst.update(btInput);
            // 獲得密文
            byte[] md = mdInst.digest();
            // 把密文轉換成十六進制的字符串形式
            int j = md.length;
            char str[] = new char[j * 2];
            int k = 0;
            for (int i = 0; i < j; i++) {
                byte byte0 = md[i];
                str[k++] = hexDigits[byte0 >>> 4 & 0xf];
                str[k++] = hexDigits[byte0 & 0xf];
            }
            return new String(str);
        } catch (Exception e) {
            return null;
        }
    }

    public static void main(String[] args){

        String MD5_String;
        MD5_String = MD5("weiqingde");
        System.out.println(MD5_String);
    }
}

注：如果需要使用這些加密算法，可以去下載apache 下的commons包，該包擁有很多對稱加密、非對稱加密、Hash加密實現工具