Information Security Experiment 1: implementation of DES encryption algorithm

One 、 Purpose and requirements of the experiment

1． Familiar with encryption 、 Decryption algorithm ; Understand the important role of encryption in communication ;

2． Encrypt the entered hexadecimal number （ Convert the input characters into integers ）, Compare input and output , When changing the input number by one bit , Compare changes in output , Explain why .

3． Realize the encryption and decryption of a file , Submit program code and execution results .

Two 、 Experimental content

This experiment uses DES The algorithm encrypts and decrypts the actual data to gain a deep understanding DES Operating principle . Analyze according to the program provided DES The realization process of the algorithm . In analyzing the key generation function 、 Encryption function （8 byte ）、 Decryption function 、 Test function and key length test function , use C/VC++ or Java Language programming to encrypt and decrypt text files .

3、 ... and 、 Experimental environment

function windows or Linux Operating system PC machine , have VC(windows)、gcc(Linux) etc. C Language compilation environment or Java Environmental Science .

Four 、 Experimental steps and result analysis

      

1. Running results

1.1、 The original document

Encrypted file

Decrypted file

1. Code

public class TestDES {
    Key key;

    public TestDES(String str) {
        getKey(str);// Generate key
    }
  
     // Generate... Based on parameters KEY
    public void getKey(String strKey) {
        try {
            KeyGenerator _generator = KeyGenerator.getInstance("DES");
            _generator.init(new SecureRandom(strKey.getBytes()));
            this.key = _generator.generateKey();
            _generator = null;
        }
        catch (Exception e) {
            throw new RuntimeException("Error initializing SqlMap class. Cause: " + e);
        }
    }

   
    public void encrypt(String file, String destFile) throws Exception {
        Cipher cipher = Cipher.getInstance("DES");
        // cipher.init(Cipher.ENCRYPT_MODE, getKey());
        cipher.init(Cipher.ENCRYPT_MODE, this.key);
        InputStream is = new FileInputStream(file);
        OutputStream out = new FileOutputStream(destFile);
        CipherInputStream cis = new CipherInputStream(is, cipher);
        byte[] buffer = new byte[1024];
        int r;
        while ((r = cis.read(buffer)) > 0) {
            out.write(buffer, 0, r);
        }
        cis.close();
        is.close();
        out.close();
    }

  
    public void decrypt(String file, String dest) throws Exception {
        Cipher cipher = Cipher.getInstance("DES");
        cipher.init(Cipher.DECRYPT_MODE, this.key);
        InputStream is = new FileInputStream(file);
        OutputStream out = new FileOutputStream(dest);
        CipherOutputStream cos = new CipherOutputStream(out, cipher);
        byte[] buffer = new byte[1024];
        int r;
        while ((r = is.read(buffer)) >= 0) {
            cos.write(buffer, 0, r);
        }
        cos.close();
        out.close();
        is.close();
    }

    public static void main(String[] args) throws Exception {
        TestDES td = new TestDES("24234");
        td.encrypt("D:/Desktop/test.txt", "D:/Desktop/test1.txt"); // encryption
        td.decrypt("D:/Desktop/test1.txt", "D:/Desktop/test2.txt"); // Decrypt
    }
}