消息摘要的概念

对消息通过一个单向Hash算法进行计算，得到一个唯一的结果。每个消息对应一个唯一结果，所有结果的长度固定。

消息摘要的分类

(1)MD5(Message Digest)消息摘要算法

(2)SHA(Secure Hash Algorithm)安全散列算法

(3)MAC(Message Authentication Code)消息认证码算法，结合了MD5和SHA的优势，同时用密钥对摘要进行加密，是一种更为安全的消息摘要算法。

日常应用

校验数据的完整性，防止在传输途中被篡改

编程使用

import java.io.File;

import java.io.FileInputStream;

import java.security.DigestInputStream;

import java.security.MessageDigest;

import javax.crypto.KeyGenerator;

import javax.crypto.Mac;

import javax.crypto.SecretKey;

import javax.crypto.spec.SecretKeySpec;

public class MessageDigestUtil {

/**

* 计算MD5值

*/

public static String encryptMD5(byte[] data) throws Exception {

MessageDigest messageDigest = MessageDigest.getInstance("MD5");//MD5,MD2

messageDigest.update(data);

return BytesToHex.fromBytesToHex(messageDigest.digest());

}

/**

* 计算文件的MD5值(指纹签名)

*/

public static String getFileMD5(String path) throws Exception {

FileInputStream fis = new FileInputStream(new File(path));

DigestInputStream dis = new DigestInputStream(fis, MessageDigest.getInstance("MD5"));

try {

byte[] buffer = new byte[1024];

int read = dis.read(buffer, 0, 1024);

while (read != -1) {

read = dis.read(buffer, 0, 1024);

}

MessageDigest md = dis.getMessageDigest();

return BytesToHex.fromBytesToHex(md.digest());

} finally {

dis.close();

fis.close();

}

}

/**

* 计算SHA值

*/

public static String encryptSHA(byte[] data) throws Exception {

MessageDigest messageDigest = MessageDigest.getInstance("SHA");//SHA,SHA1,SHA-1,SHA-256,SHA-384,SHA-512

messageDigest.update(data);

return BytesToHex.fromBytesToHex(messageDigest.digest());

}

/**

* 初始化HMAC密钥

*/

public static byte[] initHmacKey() throws Exception {

KeyGenerator keyGenerator = KeyGenerator.getInstance("HmacSHA512");//HmacMD5,HmacSHA1,HmacSHA256,HmacSHA384,HmacSHA512

return keyGenerator.generateKey().getEncoded();

}

/**

* 使用Hmac生成的密钥对数据进行加密

*/

public static String encryptHmac(byte[] data, byte[] key) throws Exception {

SecretKey secretKey = new SecretKeySpec(key, "HmacSHA512");

Mac mac = Mac.getInstance("HmacSHA512");

mac.init(secretKey);

return BytesToHex.fromBytesToHex(mac.doFinal(data));

}

public static void main(String[] args) throws Exception {

String data = "123456";

String path = "/Users/admin/Downloads/httpd-2.4.20.tar.gz";

System.out.println(data + " 的MD5值： " + MessageDigestUtil.encryptMD5(data.getBytes()));

System.out.println(path + " 的文件MD5签名： " + MessageDigestUtil.getFileMD5(path));

System.out.println(data + " 的SHA值： " + MessageDigestUtil.encryptSHA(data.getBytes()));

byte[] hmacKey = initHmacKey();

System.out.println("初始化Hmac密钥：" + BytesToHex.fromBytesToHex(hmacKey));

System.out.println(data + " 是的Hmac加密值为： " + MessageDigestUtil.encryptHmac(data.getBytes(), hmacKey));

}

}

字节码数组转成16进制字符串工具类

public class BytesToHex {

public static String fromBytesToHex(byte[] resultBytes) {

StringBuilder builder = new StringBuilder();

for (int i = 0; i < resultBytes.length; i++) {

if (Integer.toHexString(0xFF & resultBytes[i]).length() == 1) {

builder.append("0").append(

Integer.toHexString(0xFF & resultBytes[i]));

} else {

builder.append(Integer.toHexString(0xFF & resultBytes[i]));

}

}

return builder.toString();

}

}