对信息进行做数字摘要，验证信息是否被篡改！

package com.yjm.test509;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.PrivateKey;
import java.security.Signature;
import java.security.SignatureException;
import java.security.UnrecoverableKeyException;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;

public class Test {

public static void main(String[] args) {

// test();
// test1();
// test2();
// test3();
// test4();
test5();
}

private static void test5() {

try {
// RSA 密钥对  用私钥签名用公钥验签
KeyPairGenerator keyPairGenerator = KeyPairGenerator
.getInstance("RSA");

keyPairGenerator.initialize(1024);
KeyPair keyPair = keyPairGenerator.generateKeyPair();

// 获得公钥私钥
RSAPublicKey rsaPublicKey = (RSAPublicKey) keyPair.getPublic();
RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) keyPair.getPrivate();

//获得签名算法
Signature signature = Signature.getInstance("MD5withRSA");

//对数据进行签名
signature.initSign(rsaPrivateKey);
signature.update("test".getBytes());
byte[] b=signature.sign();
System.out.println("签名之后的串"+new String(b));
//对传输的数据进行验签
signature.initVerify(rsaPublicKey);
signature.update("test".getBytes());
boolean boolea = signature.verify(b);

//输出验签结果
System.out.println("验签结果: "+boolea);
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (SignatureException e) {
e.printStackTrace();
} catch (InvalidKeyException e) {
e.printStackTrace();
}
}