nonceivcbcexample.java

sip CMSEnvelopedData

package chapter2;

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

/**
 * CBC using DES with an IV based on a nonce. In this
 * case a hypothetical message number.
 */
public class NonceIvCBCExample
{   
    public static void main(
        String[]    args)
        throws Exception
    {
        byte[]          input = new byte[] { 
                0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 
                0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
                0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07 };
        byte[]		    keyBytes = new byte[] { 
                0x01, 0x23, 0x45, 0x67, (byte)0x89, (byte)0xab, (byte)0xcd, (byte)0xef };
        byte[]          msgNumber = new byte[] {
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
        
        IvParameterSpec zeroIv = new IvParameterSpec(new byte[8]);
        
        SecretKeySpec   key = new SecretKeySpec(keyBytes, "DES");
        
        Cipher          cipher = Cipher.getInstance("DES/CBC/PKCS7Padding", "BC");
        

        System.out.println("input : " + Utils.toHex(input));
        
        // encryption pass
        
        // generate IV
        
        cipher.init(Cipher.ENCRYPT_MODE, key, zeroIv);
        
        IvParameterSpec encryptionIv = new IvParameterSpec(cipher.doFinal(msgNumber), 0, 8);
        
        // encrypt message
        
        cipher.init(Cipher.ENCRYPT_MODE, key, encryptionIv);
        
        byte[] cipherText = new byte[cipher.getOutputSize(input.length)];
        
        int ctLength = cipher.update(input, 0, input.length, cipherText, 0);
        
        ctLength += cipher.doFinal(cipherText, ctLength);
        
        System.out.println("cipher: " + Utils.toHex(cipherText, ctLength) + " bytes: " + ctLength);
        
        // decryption pass
        
        // generate IV
        
        cipher.init(Cipher.ENCRYPT_MODE, key, zeroIv);
        
        IvParameterSpec decryptionIv = new IvParameterSpec(cipher.doFinal(msgNumber), 0, 8);
        
        // decrypt message
        
        cipher.init(Cipher.DECRYPT_MODE, key, decryptionIv);
        
        byte[] plainText = new byte[cipher.getOutputSize(ctLength)];

        int ptLength = cipher.update(cipherText, 0, ctLength, plainText, 0);
        
        ptLength += cipher.doFinal(plainText, ptLength);
        
        System.out.println("plain : " + Utils.toHex(plainText, ptLength) + " bytes: " + ptLength);
    }
}