加密AES / CBC / NoPadding无法产生正确的结果

Question

I have an issue with my AES encryption code. I am only getting first 16 characters encrypted correctly and remaining are not correct.

Below is my code.

import java.io.ByteArrayOutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

import javax.crypto.Cipher;
import javax.crypto.CipherOutputStream;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class AESEncryptionTest {
  public static AESEncryptionTest encryptor;

  public String MODE;
  public Cipher encCipher;

  public int blocks;

  public byte[] IV = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};

  public byte[] key;

  public static AESEncryptionTest getInstance(){
    if(encryptor == null){
      encryptor = new AESEncryptionTest();
      encryptor.init();
    }
    return encryptor;
  }

  public void init(){
   try{
     String alg = "AES/CBC/NoPadding";
     key = convert32ByteHexTo16ByteHex("C145B6D7C8EBD1A15B9FAE5D6DD7FECA");
     System.out.println("IV:" + toHex(IV, false));
     System.out.println("KEY:" + toHex(key, false));
     System.out.println("Algo:" + alg);
     IvParameterSpec encivspec = new IvParameterSpec(IV);  
     SecretKeySpec secretKey = new SecretKeySpec(key, "AES");
     encCipher = Cipher.getInstance(alg);
     encCipher.init(Cipher.ENCRYPT_MODE, secretKey, encivspec);
   } catch (Exception ex) {
     ex.printStackTrace();
   }
 }

 public void resetIV(){
   for(byte b: IV)
     b = 0x00;
 }

 public byte[] encrypt(String msg) throws Exception{  
  try{
    System.out.println("Java ersion:" + System.getProperty("java.version"));
    System.out.println("OS :" + System.getProperty("os.arch"));
    System.out.println("sun.arch.data.model x:" +   System.getProperty("sun.arch.data.model"));

    ByteArrayOutputStream ba= new ByteArrayOutputStream();
    CipherOutputStream cos = new CipherOutputStream(ba, encCipher);
    PrintWriter pw = new PrintWriter(new OutputStreamWriter(cos));
    pw.println(msg);
    pw.close();
    return ba.toByteArray();
  }catch(Exception e){
    e.printStackTrace();
    //throw new EncryptionFailedException(e.getMessage());
    throw e;
  }
 } 

 private byte[] convert32ByteHexTo16ByteHex(String hexStr){
  byte arr[] = new byte[16];
  for(int i=0; i<arr.length; i++){
    arr[i] = (byte)(Integer.parseInt(hexStr.substring(i * 2, (i*2) + 2), 16) & 0xFF);
  }
  return arr;
 }

public String toHex(byte[] arr, boolean withPrefix) {
  int offset = 0;
  int length = arr.length;
  StringBuffer sb = new StringBuffer();

  for (int i = offset; i < length; i++) {
    if (withPrefix) {
      sb.append("0x");
    }

  for (int j = 0; j < 2; j++) {
    byte nibble = (byte) (j == 0 ? arr[i] >> 4 & 0xf : arr[i] & 0xf);

    if (nibble < 10) {
      sb.append(nibble);
    } else {
      sb.append((char) ('A' + (nibble - 10)));
    }
  }

   if (i != length - 1) {
     sb.append(',');
   }
 }

 return sb.toString();
}

public static void main(String args[]){
  AESEncryptionTest util = AESEncryptionTest.getInstance();
  String rec = "DTYCOFIRE201311120001201311151531BER01 600082SBC9131G    Y103H163                                                                                         First line^Second line^Third line                                                                                                                                                                                                                              201311151531TYCOFIRE201311120001_img1.JPG                     TYCOFIRE201311120001_img2.JPG                                                                                                                         1122                          TYCOFIRE                                            \n";
  try {
    System.out.println("rec:" + rec);
    byte b[] = util.encrypt(rec);
    System.out.println("encrypted:" + new String(b));
  } catch (Exception e) {
  e.printStackTrace();
  }
}
}

When i compare the text only 16 characters converted correctly. remaining are not matching. I confirmed this by passing first 16 characters.

Can you please let me know what went wrong in the above program?

Java version:1.6.0_32
OS :x86
sun.arch.data.model x:32

Answer 1

Block cyphers, like AES, encrypt whole blocks. A block is 128 bits (=16 bytes) for AES. Unless your message is an exact number of blocks, then the last block will be too short and encryption will fail at that point. Padding is used to extend the last part of your message to the next block boundary. For Java in CBC mode use PKCS5 padding for both encryption and decryption. It will be added, and removed, automatically and you can then forget about it.