@changedi
2016-09-02T09:31:21.000000Z
字数 7014
阅读 2394
Java
安全
消息摘要(Message Digest)又称为数字摘要(Digital Digest)。它是一个唯一对应一个消息或文本的固定长度的值,它由一个单向Hash加密函数对消息进行作用而产生。如果消息在途中改变了,则接收者通过对收到消息的新产生的摘要与原摘要比较,就可知道消息是否被改变了。因此消息摘要保证了消息的完整性。 消息摘要采用单向Hash 函数将需加密的明文"摘要"成一串128bit的密文,这一串密文亦称为数字指纹(Finger Print),它有固定的长度,且不同的明文摘要成密文,其结果总是不同的,而同样的明文其摘要必定一致。这样这串摘要便可成为验证明文是否是"真身"的"指纹"了。 <<百度百科>>
消息摘要其实是我们日常开发中经常遇到的,比如MD5算法就是一种摘要。它是Java安全提供者体系中最简单的标准引擎。本文不会讨论算法本身,只关注Java语言体系中的实现和使用方法。具体算法原理,后续撰文学习并补充。
消息摘要通过MessageDigest类实现。消息摘要通过getInstance()方法获取算法实例。通过update()方法为消息摘要增加内容字节。根据digest()方法利用累计的内容字节计算最后的摘要。
下面的test列出了一些细节:
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;
import org.apache.commons.codec.binary.Hex;
public class MessageDigestTest {
private static String TEST_DATA = "i am a test";
public static void main(String[] args)
throws NoSuchAlgorithmException, UnsupportedEncodingException {
MessageDigest md = MessageDigest.getInstance("SHA");
print(md);
md = MessageDigest.getInstance("MD5");
print(md);
md = MessageDigest.getInstance("MD2");
print(md);
md = MessageDigest.getInstance("SHA-256");
print(md);
md = MessageDigest.getInstance("SHA-384");
print(md);
md = MessageDigest.getInstance("SHA-224");
print(md);
md = MessageDigest.getInstance("SHA-512");
print(md);
}
private static void print(MessageDigest md) throws UnsupportedEncodingException {
System.out.println("Algorithm:\t" + md.getAlgorithm());
System.out.println("\tProvider:\t" + md.getProvider());
long start = System.nanoTime();
md.update(TEST_DATA.getBytes("UTF-8"));
byte[] digest = md.digest();
long time = System.nanoTime() - start;
System.out.println("\tTime cost:\t" + time + "ns");
System.out.println("\tByte length:\t" + digest.length);
String digestBase64Str = Base64.getEncoder().encodeToString(digest);
System.out.println("\tBase64:\t" + digestBase64Str + "\tlen:\t" + digestBase64Str.length());
String digestHexStr = Hex.encodeHexString(digest);
System.out.println("\tHex:\t" + digestHexStr + "\tlen:\t" + digestHexStr.length());
}
}
输出结果如下:
Algorithm: SHA
Provider: SUN version 1.8
Time cost: 432582ns
Byte length: 20
Base64: Bj5BsD+J+PLpYZYVDR+14WwSKlg= len: 28
Hex: 063e41b03f89f8f2e96196150d1fb5e16c122a58 len: 40
Algorithm: MD5
Provider: SUN version 1.8
Time cost: 46030ns
Byte length: 16
Base64: dCVplUXLIKBlw/aWvoOCyA== len: 24
Hex: 7425699545cb20a065c3f696be8382c8 len: 32
Algorithm: MD2
Provider: SUN version 1.8
Time cost: 80611ns
Byte length: 16
Base64: v4z32/PgSXZCrWvnOcRiaQ== len: 24
Hex: bf8cf7dbf3e0497642ad6be739c46269 len: 32
Algorithm: SHA-256
Provider: SUN version 1.8
Time cost: 205859ns
Byte length: 32
Base64: lRctjSY3GOo6erswsyheP21CNtAAGxnsUHVF17u7RYg= len: 44
Hex: 95172d8d263718ea3a7abb30b3285e3f6d4236d0001b19ec507545d7bbbb4588 len: 64
Algorithm: SHA-384
Provider: SUN version 1.8
Time cost: 258382ns
Byte length: 48
Base64: /B642f1Y+PPKgeIJHFpbEDLJwX2nqWaMaC8nVQuboRWN5MZeKpGaLiySWUEr4xB9 len: 64
Hex: fc1eb8d9fd58f8f3ca81e2091c5a5b1032c9c17da7a9668c682f27550b9ba1158de4c65e2a919a2e2c9259412be3107d len: 96
Algorithm: SHA-224
Provider: SUN version 1.8
Time cost: 76539ns
Byte length: 28
Base64: 6m2pv1G0lnWlKO4ahn7iJAQF8XMo5cHR3LBO3w== len: 40
Hex: ea6da9bf51b49675a528ee1a867ee2240405f17328e5c1d1dcb04edf len: 56
Algorithm: SHA-512
Provider: SUN version 1.8
Time cost: 143649ns
Byte length: 64
Base64: Vv6LL9QqfeCq1ClbN8JdMTcU1PzUbsRQKgmc7vVDbcHTB6i/SryXIjWcRcrfYa6n2QxstmSwUY9AME3pTmykNw== len: 88
Hex: 56fe8b2fd42a7de0aad4295b37c25d313714d4fcd46ec4502a099ceef5436dc1d307a8bf4abc9722359c45cadf61aea7d90c6cb664b0518f40304de94e6ca437 len: 128
消息摘要实现是通过Java自己Sun的实现来做的。我们常见的是MD5和SHA算法。
考虑到消息摘要的不安全性——拿到原文并知道算法,就可以得到正确的消息摘要。人们又加入了密钥元素,得到了安全消息摘要——MAC(Message Authentication Code)。MAC的特点是仅通过原文是无法计算出安全消息摘要的。还需要一个双方都知道的消息密钥。如果有人修改了消息本体,又修改了消息摘要,但是因为没有使用密钥,那么将被发现破坏了数据。计算MAC的方法有很多,但是核心Java API没有相关实现。Java的实现主要是通过JCE提供者来实现的。Mac类对应消息摘要的MessageDigest类。计算消息摘要时需要一个密钥。密钥的管理是另一个话题了。这里主要讲MAC的算法,JCE实现主要基于HmacSHA1和HmacMD5。具体provider提供了哪些MAC相关的算法,它们比较如何,见下面的代码:
package com.taobao.cd.security;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;
import javax.crypto.KeyGenerator;
import javax.crypto.Mac;
import javax.crypto.SecretKey;
import org.apache.commons.codec.binary.Hex;
public class MacTest {
public static String TEST_DATA = "I am test";
public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeyException {
// TODO Auto-generated method stub
Mac mac = Mac.getInstance("HmacSHA1");
print(mac);
mac = Mac.getInstance("HmacMD5");
print(mac);
mac = Mac.getInstance("SslMacMD5");
print(mac);
mac = Mac.getInstance("HmacSHA384");
print(mac);
mac = Mac.getInstance("HmacSHA256");
print(mac);
mac = Mac.getInstance("HmacSHA224");
print(mac);
mac = Mac.getInstance("SslMacSHA1");
print(mac);
mac = Mac.getInstance("HmacSHA512");
print(mac);
}
private static void print(Mac mac) throws NoSuchAlgorithmException, InvalidKeyException {
System.out.println("Algorithm:\t" + mac.getAlgorithm());
System.out.println("\tProvider:\t" + mac.getProvider());
KeyGenerator kg = KeyGenerator.getInstance("DES");
SecretKey key = kg.generateKey();
long start = System.nanoTime();
mac.init(key);
mac.update(TEST_DATA.getBytes());
byte[] digest = mac.doFinal();
long time = System.nanoTime() - start;
System.out.println("\tTime cost:\t" + time + "ns");
System.out.println("\tByte length:\t" + digest.length);
String digestBase64Str = Base64.getEncoder().encodeToString(digest);
System.out.println("\tBase64:\t" + digestBase64Str + "\tlen:\t" + digestBase64Str.length());
String digestHexStr = Hex.encodeHexString(digest);
System.out.println("\tHex:\t" + digestHexStr + "\tlen:\t" + digestHexStr.length());
}
}
输出如下:
Algorithm: HmacSHA1
Provider: SunJCE version 1.8
Time cost: 259396ns
Byte length: 20
Base64: SVaesT3JpL9Emz5O40aZhpUrX5s= len: 28
Hex: 49569eb13dc9a4bf449b3e4ee3469986952b5f9b len: 40
Algorithm: HmacMD5
Provider: SunJCE version 1.8
Time cost: 136070ns
Byte length: 16
Base64: hBDkDPJ1CpyYqvFN48chqQ== len: 24
Hex: 8410e40cf2750a9c98aaf14de3c721a9 len: 32
Algorithm: SslMacMD5
Provider: SunJCE version 1.8
Time cost: 174089ns
Byte length: 16
Base64: YiEubyE7y+M4JesHQOAV7A== len: 24
Hex: 62212e6f213bcbe33825eb0740e015ec len: 32
Algorithm: HmacSHA384
Provider: SunJCE version 1.8
Time cost: 648249ns
Byte length: 48
Base64: GLic/lwKBA1DdQVbNF5y7L/H8o+0gcO1n02JcdUJMnE9MRwyfHWamEsAJL3ycfFy len: 64
Hex: 18b89cfe5c0a040d4375055b345e72ecbfc7f28fb481c3b59f4d8971d50932713d311c327c759a984b0024bdf271f172 len: 96
Algorithm: HmacSHA256
Provider: SunJCE version 1.8
Time cost: 26007ns
Byte length: 32
Base64: 7LGdb6W8WPYfOXx0WQQ8f35zSGCxs/6op6eOqStuGxA= len: 44
Hex: ecb19d6fa5bc58f61f397c7459043c7f7e734860b1b3fea8a7a78ea92b6e1b10 len: 64
Algorithm: HmacSHA224
Provider: SunJCE version 1.8
Time cost: 125344ns
Byte length: 28
Base64: adoBxnZuCle/ip4FyfCgiQUCmlaN1+RDch9Q9g== len: 40
Hex: 69da01c6766e0a57bf8a9e05c9f0a08905029a568dd7e443721f50f6 len: 56
Algorithm: SslMacSHA1
Provider: SunJCE version 1.8
Time cost: 50672ns
Byte length: 20
Base64: RxCsQguxNXgtqcobgqWdvJeYTKo= len: 28
Hex: 4710ac420bb135782da9ca1b82a59dbc97984caa len: 40
Algorithm: HmacSHA512
Provider: SunJCE version 1.8
Time cost: 365908ns
Byte length: 64
Base64: /Vf5JsSle43/t4aUMkDfdDeUFg3CA0OQAt5izo0bgoUmaVrVOv3tjTLwmrrL/3kACVn38aIDSAIlz8725gl6lA== len: 88
Hex: fd57f926c4a57b8dffb786943240df743794160dc203439002de62ce8d1b828526695ad53afded8d32f09abacbff79000959f7f1a203480225cfcef6e6097a94 len: 128
这里使用的key是通过KeyGenerator生成的。在实际应用中,应该有一方来生成并导出到可管理的KeyStore,使用方载入Keystore再进行摘要生成和校验。