使用数字签名验证文件是否被修改

基本原理：

发送方：

1.     生成公钥和私钥并保存至文件public.key和private.key。

2.     根据要发送的文件内容生成签名并写入文件signature.dtx。

3.     将公钥文件、签名文件和要发送的文件一起发送给接受方。

接受方：

1.     读取发送方发送的公钥文件

2.     读取发送方发送的签名文件。

3.     读取发送方发送的文件。

4.     根据发送方发送的公钥对发送方发送的文件进行签名。

5.     对比生成的签名和发送方发送的签名是否一致。

 

代码：

package com.security.example.example1;   import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.security.InvalidKeyException; import java.security.KeyPair; import java.security.KeyPairGenerator; import java.security.NoSuchAlgorithmException; import java.security.PrivateKey; import java.security.PublicKey; import java.security.Signature; import java.security.SignatureException;   import org.apache.log4j.Logger;   /**  * 发送方。  * @author lucky star  *  */ public class Sender {          private static Logger log = Logger.getLogger(Sender.class);                   public void writeKeysToFiles(String privateFileName,String publicFileName)throws NoSuchAlgorithmException, FileNotFoundException, IOException {                    KeyPairGenerator keygen = KeyPairGenerator.getInstance("DSA");                    keygen.initialize(1024);                    KeyPair kp = keygen.generateKeyPair();                    PrivateKey privateKey = kp.getPrivate();                    PublicKey publicKey = kp.getPublic();                    ObjectOutputStream out_private = new ObjectOutputStream(new FileOutputStream(privateFileName));                    out_private.writeObject(privateKey);                    out_private.close();                                       ObjectOutputStream out_public = new ObjectOutputStream(new FileOutputStream(publicFileName));                    out_public.writeObject(publicKey);                    out_public.close();                                       log.debug("已生成私钥文件：" + privateFileName +",公钥文件：" + publicFileName);          }                   /**           * 读取私钥文件得到私钥，并根据文件内容生成签名并写入签名文件。           * @param privateFile：私钥文件。           * @param f：要发送的文件           * @throws FileNotFoundException：如果文件未找到           * @throws IOException：如果出现读写异常           * @throws ClassNotFoundException：如果类未找到           * @throws NoSuchAlgorithmException：如果没有此算法           * @throws InvalidKeyException：如果私钥不可用           * @throws SignatureException：如果签名失败           */          public void send(File privateFile,File sigendFile,File f) throws FileNotFoundException, IOException, ClassNotFoundException, NoSuchAlgorithmException, InvalidKeyException, SignatureException {                    if (privateFile==null) {                             thrownew FileNotFoundException("没有找到私钥文件！");                    }                    if (f ==null) {                             thrownew FileNotFoundException("没有找到要加密的文件！");                    }                    // 读取文件，得到私钥                    ObjectInputStream in = new ObjectInputStream(new FileInputStream(privateFile));                    PrivateKey privateKey = (PrivateKey) in.readObject();                    in.close();                                       // 根据文件生成签名，并保存到文件signature.dxt                    byte[] data =new byte[(int) f.length()];                    FileInputStream fis = new FileInputStream(f);                    fis.read(data);                    fis.close();                                       Signature sign = Signature.getInstance("DSA");                    sign.initSign(privateKey);                    sign.update(data);                    // 生成签名                    byte[] signedBytes = sign.sign();                    // 将签名写入文件                    FileOutputStream fos = new FileOutputStream(sigendFile);                    fos.write(signedBytes,0,signedBytes.length);                    fos.close();                                       log.debug("根据文件内容生成签名并写入签名文件完毕！");                    log.debug("签名文件写入到" + sigendFile.getName());          }                   public static void main(String[] args) {                    // 私钥文件                                      String privateFileName = "private.key";                                      // 公钥文件                                      String publicFileName = "public.key";                                      // 签名文件                                      String signedFileName = "signature.dtx";                                      // 发送方要发送的文件。                                      File f = new File("d:/test.xml");                                      File privateFile = new File(privateFileName);                                      File sigendFile = new File(signedFileName);                                                                           try {                                                Sender sender = new Sender();                                                // 发送方将公钥和私钥保存到文件private.key和public.key                                                sender.writeKeysToFiles(privateFileName, publicFileName);                                                // 发送方根据文件内容生成签名并写入signature.dtx                                                sender.send(privateFile,sigendFile,f);                                      } catch (NoSuchAlgorithmException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      } catch (FileNotFoundException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      } catch (IOException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      } catch (InvalidKeyException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      } catch (SignatureException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      } catch (ClassNotFoundException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      }          } }

 

接受方：

package com.security.example.example1;   import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.io.ObjectInputStream; import java.security.InvalidKeyException; import java.security.NoSuchAlgorithmException; import java.security.PublicKey; import java.security.Signature; import java.security.SignatureException;   import org.apache.log4j.Logger;   /**  * 接受方。  * @author lucky star  *  */ public class Receiver {          private static Logger log = Logger.getLogger(Receiver.class);          /**           * 接受方读取发送方的公钥文件得到公钥，并以公钥验证签名。           * @param publicKeyFile:公钥文件。           * @param f：发送方发送的文件。           * @return：签名是否验证OK。           * @throws NoSuchAlgorithmException：如果没有此算法。           * @throws FileNotFoundException：如果文件未找到。           * @throws IOException：如果读写异常           * @throws ClassNotFoundException：如果类未找到           * @throws InvalidKeyException：如果公钥不可用           * @throws SignatureException：如果签名失败           */          public boolean receive(File publicKeyFile,File signedFile,File f) throws NoSuchAlgorithmException, FileNotFoundException, IOException, ClassNotFoundException, InvalidKeyException, SignatureException {                    if (publicKeyFile ==null) {                             thrownew FileNotFoundException("公钥文件未找到！");                    }                    if (f ==null) {                             thrownew FileNotFoundException("发送方没有发送文件！");                    }                    // 读取公钥文件得到公钥                    ObjectInputStream in = new ObjectInputStream(new FileInputStream(publicKeyFile));                    PublicKey pk = (PublicKey) in.readObject();                    in.close();                                       // 读取发送方发送的文件，读入字节数组                    byte[] data =new byte[(int) f.length()];                    FileInputStream fis = new FileInputStream(f);                    fis.read(data);                                       // 读取发送方的签名文件                    byte[] signData =new byte[(int) signedFile.length()];                    FileInputStream fis2 = new FileInputStream(signedFile);                    fis2.read(signData);                    fis2.close();                                       // 使用发送方的公钥验证签名                    Signature sign = Signature.getInstance("DSA");                    sign.initVerify(pk);                    sign.update(data);                    return sign.verify(signData);          }                   public static void main(String[] args) {                                      // 公钥文件                                      String publicFileName = "public.key";                                      // 签名文件                                      String signedFileName = "signature.dtx";                                      // 发送方发送的文件。                                      File f = new File("d:/test.xml");                                      File publicFile = new File(publicFileName);                                      File sigendFile = new File(signedFileName);                                                                           try {                                                Receiver recv = new Receiver();                                                // 接受方读取发送方提供的公钥文件验证签名是否一致                                                boolean isOk = recv.receive(publicFile,sigendFile, f);                                                if (isOk) {                                                         log.info("接受方验证文件无篡改！");                                                }                                                else {                                                         log.info("接受方验证文件被篡改！");                                                }                                      } catch (NoSuchAlgorithmException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      } catch (FileNotFoundException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      } catch (IOException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      } catch (InvalidKeyException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      } catch (SignatureException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      } catch (ClassNotFoundException e) {                                                // TODO Auto-generated catch block                                                e.printStackTrace();                                      }          } }

 

1.     运行Sender.java，生成公钥和私钥、签名写入文件。

2.     运行Receiver.java，使用发送方的公钥验证签名。

 

测试：执行1，生成3个文件：

调试信息：

DEBUG [main] - 已生成私钥文件：private.key,公钥文件：public.key

DEBUG [main] - 根据文件内容生成签名并写入签名文件完毕！

DEBUG [main] - 签名文件写入到signature.dtx

 

执行2，输出结果：

INFO [main] - 接受方验证文件无篡改！

 

现在修改文件d:/test.xml，再次执行2，输出结果：

INFO [main] - 接受方验证文件被篡改！