Java逐字加密

Question

I'm trying to take in a long string and encrypt it using the following code:

import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.io.*;

public class AESEncrypt {

    /**
     * Turns array of bytes into string
     * 
     * @param buf
     *            Array of bytes to convert to hex string
     * @return Generated hex string
     */
    public static String asHex(byte buf[]) {
        StringBuffer strbuf = new StringBuffer(buf.length * 2);
        int i;

        for (i = 0; i < buf.length; i++) {
            if (((int) buf[i] & 0xff) < 0x10)
                strbuf.append("0");

            strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
        }

        return strbuf.toString();
    }

    public static byte[] hexStringToByteArray(String s) {
        int len = s.length();
        byte[] data = new byte[len / 2];
        for (int i = 0; i < len; i += 2) {
            data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character
                    .digit(s.charAt(i + 1), 16));
        }
        return data;
    }

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

        String message = "Test text!";

        // Get the KeyGenerator
        KeyGenerator kgen = KeyGenerator.getInstance("AES");
        kgen.init(128); // 192 and 256 bits may not be available

        // Generate the secret key specs.
        SecretKey skey = kgen.generateKey();
        byte[] raw = skey.getEncoded();

        SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
        System.out.println("Key: " + asHex(raw));

        // Instantiate the cipher

        Cipher cipher = Cipher.getInstance("AES");

        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

        byte[] encrypted = cipher.doFinal((args.length == 0 ? message : args[0]).getBytes());
        System.out.println("encrypted string: " + asHex(encrypted));

    }
}

However, I would like to encrypt word by word and print out the encrypted text as such:

Original string -> Test text!

Encrypted string -> 29f84h2f 23f9f92jf3

I couldn't find any examples online that could help me out. Is there anyway I can achieve this?

Answer 1

AES is a block cypher, and it uses 16 byte blocks. It does not work in words, but in fixed blocks. If you want to split up your text into varying size words then you will likely get closer to what you want by using either a stream cypher, such as RC4, or alternatively AES in CTR mode, which effectively turns AES into a stream cypher. Stream cyphers do not work in blocks, but in bytes. You can take 3 bytes off the stream for a 3 letter word, or nine bytes off the stream for a 9 letter word.

You will need to work out what to do with spaces, punctuation etc between words. You will also need to think about how often you re-key the cypher. Do you want to re-key for every individual word, or do you just re-key at the start of each string? As with any stream cypher, never ever use the same key twice.

Answer 2

Try as below example; Actually, It just need to used StringTokenizer. Firstly you have to token your target string. After that, encrypt the token string.

import java.util.StringTokenizer;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;


public class AES {
    public static String asHex(byte[] buf) {
        StringBuffer strbuf = new StringBuffer(buf.length * 2);
        int i;

        for (i = 0; i < buf.length; i++) {
            if (((int)buf[i] & 0xff) < 0x10)
                strbuf.append("0");
            strbuf.append(Long.toString((int)buf[i] & 0xff, 16));
        }

        return strbuf.toString();
    }

    public static void main(String[] args) throws Exception {
        KeyGenerator kgen = KeyGenerator.getInstance("AES");
        kgen.init(128); // 192 and 256 bits may not be available
        // Generate the secret key specs.
        SecretKey skey = kgen.generateKey();
        byte[] raw = skey.getEncoded();

        SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

        String target = "This is just an example";
        StringTokenizer token = new StringTokenizer(target);
        while(token.hasMoreTokens()) {
            String temp = token.nextToken();
            byte[] encrypted = cipher.doFinal((args.length == 0 ?  temp : args[0]).getBytes());
            System.out.println(asHex(encrypted) + " ");
        }
    }
}

Output :

    d40186eab04d10e299801e7ad9046c06 6a71265c768a3b6e1f1a8f891d621c1d 735e3f54c8ad7242466e3517e8dd1659 5216643345db0f0c12f65c66c5363be3 b823355d5bb31bf092df98e18fa8001c